Advances and enhanced functionalities of anion-controlled new inorganic materials-ANIM 4

Resume : The proton, H+, is unstable due to its extremely high charge density and exists as a hydroxide anion (OH-) in the oxide. Therefore, by inserting a proton into the oxide, the metal-oxide bonding can be 'disproportionated' locally and at times selectively. In my talk, I will show that electrochemical proton insertion can serve as a playground for new topochemical reactions. We have recently found that SrCoO2.5 thin films are converted to SrCoO2 by dehydration of HSrCoO2.5 (or SrCoO1.5(OH)) at 350°C. SrCoO2 forms square (or four-legged) spin tubes composed of tetrahedra, in contrast to the conventional infinite-layer structure [1]. Detailed analyses suggest the importance of the destabilization of the SrCoO2.5 precursor (as seen from the distorted Co4(OH)2 octahedron vs CoO6 in the precursor) by electrochemical protonation that can greatly alter reaction energy landscape, and its gradual dehydration (H1–xSrCoO2.5–x/2) for the SrCoO2 formation. Given the applicability of electrochemical protonation to a variety of transition metal oxides, this simple process, electrochemical protonation combined with thermal dehydration, widens possibilities to explore novel functional oxides.Interestingly, SrCoO2 cannot be obtained by metal hydride (e.g., CaH2), which is a well-known reduction method of oxides, i.e., it can be regarded as a powerful reduction reaction of oxides as an alternative to metal hydride. Although SrCoO2 (d6, S=2) is a Mott insulator, it has an even-legged ladder (tube) structure, which can be expected to have properties such as high-temperature superconductivity by carrier doping [2]. From this point of view, we synthesized the Nd-doped Brownmillerite phase at the Sr site and performed the same electrochemical protonation and dehydration reactions, revealing that the structure was converted to an infinite layer structure, instead of a four-legged spin tube structure. [1] Haobo Li, Hiroshi Takatsu et al., J. Am. Chem. Soc. 143, 17517-17525 (2021). [2] Haobo Li, Hiroshi Takatsu et al., in preparation.

Resume : Intercalation and deintercalation are one of the most powerful ways to modify extended solid-state materials. These topochemical processes often involve oxidation or reduction of host lattices to compensate added or removed electric charges. Conventionally, these redox reactions resulted in different oxidation states of constituent transition metal cations. For instance, we have recently reported that the layered strontium manganese copper oxysulphide, where perovskite-type strontium manganese oxide layers alternate with anti-PbO type copper sulphide layers, was subject to deintercalation of its cuprous cations up to 11% upon the reaction with iodine. Accordingly, its mixed-valence manganese (with nominal oxidation state of 2.5+) was partially oxidised, resulting in drastic change in its AFM magnetic ordering within the square-planar manganese oxide layers [J. N. Blandy et al. APL Mater. 2015, 3, 041520]. In the present study, we attempt to achieve much greater extent of copper deintercalation from that intergrowth oxysulphide system. Our multistep topochemical synthesis successfully removed most of cuprous cations from the host lattice up to 80-90 %. Diffraction and TEM analyses of the product showed that the structural integrity of the perovskite-type manganese oxide layers was retained while its interlayer spacing shrunk over 0.7 Å, indicating “collapse” of the adjacent copper sulphide slabs. Such a drastic deintercalation may involve not only cation redox but also oxidation of sulphur anions, leading S-S bond formation [G. Assat, J.-M. Tarascon, Nat. Energy 2018, 3, 373]. In the presentation, that redox competition will be discussed in association with its resultant structural complexity.

Resume : Alkaline earth oxynitridosilicats are important candidates for host materials of oxynitride phosphors applied in white LEDs. Their preparation method is generally a solid state reaction using AECO3 (AE = Ca, Sr, Ba), SiO2 and Si3N4. The reaction temperature is higher than 1300 deg C since diffusion of elements such as covalent nitrogen should be enhanced at higher temperature. Several approaches using a flux material or fine precursor powders have been studied to lower the reaction temperature. Recently, low temperature formation of oxynitride perovskites, SrTaO2N and SrNbO2N, have been proposed, in which alkaline earth carbodiimides appeared as an intermediate phase [1]. Here we report a new synthesis method lowering the formation temperature of alkaline earth oxynitridosilicates using alkaline earth carbodiimides and SiO2 without Si3N4. The carbodiimides were used as both alkaline earth and nitrogen sources. Barium oxynitridosilicates, Ba3Si6O12N2 and Ba2Si6O9N4, were obtained from a mixture of BaCN2 and SiO2 at 800 deg C, which is several hundred degrees lower than the temperature required in a solid state reaction using Si3N4 [2]. The phase ratio between the Ba3Si6O12N2 and Ba3Si6O9N4 was controlled by changing the reaction temperature, duration, and reaction atmosphere. Almost single phase of Ba3Si6O12N2 was obtained at 800 deg C for 15h under N2 atmosphere and the product changed to Ba3Si6O9N4 after 50 h duration at 800 deg C. Reaction between SrCN2 and SiO2 was also studied for synthesis of SrSi2O2N2 and the oxynitride was obtained at 900 deg C under N2 flow. Both barium and strontium oxynitridosilicates doped with Eu were prepared from Eu doped alkaline earth carbodiimides and showed broad green photoluminescence. Alkaline earth carbodiimides are promising nitrogen sources for a low-temperature and energy-efficient process that form oxynitride compounds. References [1] Y. Masubuchi, et al., Chem. Lett., 47 (2018) 31-33. [2] Y. Masubuchi, et al., Dalton Trans., 50 (2021) 5883-5889.

Resume : Stability under reducing working atmospheres is an important quality in electrode materials for solid oxide fuel cells. For Ruddlesden-Popper manganites LaxSr2-xMnO4-δ with 0.25 ≤ x ≤ 0.6, this structure preservation has been demonstrated by in situ high-temperature neutron and X-ray powder diffraction. [1] However, in situ and ex situ 3D electron diffraction now reveal that La0.5Sr1.5MnO4 nevertheless undergoes unexpected structure transformations upon heating in diluted hydrogen gas. While previously unobserved, the extra reflections disclosing these transformations can be easily picked up by electron diffraction. This is because electron diffraction allows to obtain 2D single-crystal diffraction patterns for submicron sized crystals, for which X-ray and neutron diffraction can only produce 1D powder data that are much more difficult to interpret. Using a dedicated environmental holder, 3D electron diffraction shows that La0.5Sr1.5MnO4 partially transforms from its pristine K2NiF4-type symmetry to a perovskite phase, when it is heated inside the transmission electron microscope in diluted hydrogen. When the material is annealed ex situ in diluted H2 /Ar, the same phenomenon is detected for a part of the crystals, while other crystals show the occurrence of a superstructure accompanying oxygen-vacancy order. This oxygen-vacancy order was not observed in any of the in situ experiments. Similarly, in situ and ex situ 3D electron diffraction show different structural behaviour for the gas reduction of Sr2MnO4 when this happens inside or outside the electron microscope: Sr2MnO4 transforms to the monoclinic P21/c supercell known in literature [2] when reduced ex situ, but maintains the tetragonal symmetry when reduced in situ. On the other hand, LaSrMnO4 and La0.25Sr1.75MnO4 indeed show no differences in their space groups upon reduction. In-depth study of the diverging reduction behaviour inside and outside the microscope could offer new insights on the degradation of real life working electrodes, and could help to optimize their performance life time. [1] Sandoval, M., Pirovano C., Capoen, E., Jooris, R., Porcher, F., Roussel, P., Gauthier, G. (2017). Int. J. Hydrog. Energy. 42 (34), 21930-21943. [2] Broux, T., Bahout, M., Hernandez, O., Tonus, F., Paofai, S., Hansen, T., Greaves, C. (2013). Inorg. Chem. 52 (2), 1009-1017. Financial support is acknowledged from FWO I003218N, University of Antwerp BOF TOP 38689 and the European Commission NanED Grant number 956099.

Resume : Oxide chalcogenides and oxide pnictides have become of increasing interest following the discovery of the iron-based pnictide and chalcogenide superconductors. In this presentation the synthesis, crystal structures and physical properties of a series of layered oxide chalcogenides and oxide arsenides will be described and the changes in magnetic ordering and other physical properties will be described as functions of temperature and composition, and related to changes in crystal structure. In particular, the control that can be exerted over the structural and physical properties in the series A2MO2B2Ch2 (A = electropositive metal, M = transition metal, B = coinage metal, Ch = chalcogenide) will be described. This ranges from tuning the oxidation state of the transition metal using soft chemical approaches to changing the coinage metal content, and tuning the spin state of the transition metal by tuning the ligand field via chemical substitution on various crystallographic sites.

Resume : Some transition-metal oxides including cations with unusual high valence states and/or mixed valence states show charge transitions to relieve the electronic instability. Significant changes in magnetic and transport properties are often observed at the charge transition temperature. We found in this study that entropies of the compounds also change by the charge transition, giving rise to large latent heat. The observed giant entropy changes can be utilized through caloric effects, which will be used in thermal control devices. Large barocaloric effects in NdCu3Fe4O12 and multiple caloric (both barocaloric and magnetocaloric) effects in BiCu3Cr4O12 will be reported. Strong correlation in charge-spin-lattice degrees of freedom in the oxides are crucial for the novel property.

Resume : GaM4X8 (M = Mo, V and X = S, Se) lacunar spinel compounds are important materials with negative magnetoresistance, Jahn-Teller driven ferroelectricity, Néel-type skyrmion lattice and Mott-Insulator transitions.[1] However, no oxide analogue has been reported before. We have discovered the chemical equivalent oxide GaV4O8.[2] It crystallizes in a hexagonal structure, S.G. P63mc, with a = 5.6947(1) Å and c = 9.3863(1) Å cell parameters. Although the cooperative polar arrangement of GaO4 tetrahedra (Td) remains, it differs from the lacunar spinel chalcogenides in the X stacking sequence (ABC) being ABCB for the oxide. The structure can be described as a kagome lattice with a strong breathing anisotropy (2.52 Å vs 3.14 Å for V-V distances) and an extra vanadium on the top of the opened cluster contrarily to contracted V4 Tds in the sulfide. Analogous to the sulfide, which shows a structural transition at TS = 42 K and a magnetic transition at TC = 13 K, the oxide presents a Jahn-Teller instability with TS = 68 K and an antiferromagnetic transition at TN = 35 K. Neutron diffraction studies show a complex magnetic structure with an unexpected k = [¼ ¼ 0] propagation vector with an original spin-orbital-charge texture, from the coexistence of orbital molecules on the vanadium trimers and localized electrons on the remaining vanadium atoms. The results of this new chalcogenide will be presented and compared with its siblings. [1] I. Kezsmarki, et al. Nat. Mat. 14 (2015) 1116. [2] C. Aguilar-Maldonado et al. Mater. Horiz, 8 (2021) 2325-2329.

Resume : Topochemical synthesis is a developing field of solid-state chemistry, which provides access at low temperature to (new) phases with interesting properties and functionalities. For example, the topochemical intercalation of copper in the material La2O2S2 leads to the low temperature synthesis of the known transparent conductor La2O2Cu2S2 [1]. The oxysulfide La2O2S2 is formed by sulfur (S2)2- dimers sandwiched between the [La2O2]2+ layers, thus copper donates electrons to the sulfur dimers which breaks them to form a two-dimensional layer in situ. However, when we use an alkali metal (Na, K, Rb) instead of copper, we found that this one is not intercalated. Instead the alkali metal takes out one sulfur from La2O2S2 by a topochemical pathway to form a metastable compound oA-La2O2S [2]. This work aims to present the synthesis and the structure of this new metastable compound and to give a glimpse at the rich topochemistry of sulfur deintercalation from polychalcogenide compounds in order to synthesise new functional materials. [1] S. Sasaki, D. Driss. E. Grange, J.Y. Mevellec, et al, Angewandte Chemie. 2018, 130,41. [2] S. Sasaki, M.T Caldes, C. Guillot-Deudon, I. Braems, et al, Nat Commun. 2021, 12, 3605.

Resume : Iron-based superconductors (IBSC) are made of building blocks containing iron atoms associated to a pnictogen or chalcogen element (P, As and S, Se, Te respectively)1. The recent discovery of superconductivity in LaFeSiH (Tc=10K) by solid-gas hydrogenation of LaFeSi, i.e. the first IBSC containing FeSi as conductive layer, has motivated the research of new IBSC by topotactic intercalation of light element in intermetallics2. However, fluorine insertion has remained elusive so far since the strong reactivity of this atypical element, the most electronegative one, tends to produce the chemical decomposition of intermetallic compounds. Here, we also introduce a new topochemical method to intercalate fluorine atoms into intermetallics, using perfluorocarbon reactant with covalent C-F bonds. We demonstrate the potential of this novel approach with the synthesis of non-stoichiometric mixed anion (Si-F) LaFeSiFx single-crystals in which we observe the coexistence of ionic and metallo-covalent blocks in interaction through inductive effects3. In addition, we show the emergence of superconductivity across this series that thus extends the family of IBSC to novel FeSi-based materials beyond the conventional ferropnictides and chalcogenides. References 1 H. Hosono, K. Tanabe, E. Takayama-Muromachi, H. Kageyama, S. Yamanaka, H. Kumakura, M. Nohara, H. Hiramatsu, and S. Fujitsu, Sci. Technol. Adv. Mater. 16, 033503 (2016). 2 F. Bernardini, G. Garbarino, A. Sulpice, M. Nuñez-Regueiro, E. Gaudin, B. Chevalier, M-A. Méasson, A. Cano, and S. Tencé, Phys. Rev. B, 97, 100504(R) (2018). 3 J-B. Vaney, B. Vignolle, A. Demourgues, E. Gaudin, E. Durand, C. Labrugère, F. Bernardini, A. Cano, S. Tencé, Nature Comm. (2022).

Resume : Designing polar structures is a key challenge in functional materials research, for example, to meet the needs of data storage materials (in ferroic and multiferroic systems[1]), and in energy materials (to minimise electron-hole recombination in semiconductors[2]). Mixed-anion materials provide an avenue to design polar structures[3] by several means including:  Shifting anion sites (e.g. by geometric factors) in the anion sublattice to break inversion symmetry;[4]  Anion substitutions to give non-centrosymmetric units in a heteranionic lattice.[5] This talk explores the methods and challenges associated with these routes in mixed-anion oxyfluorides and oxychalcogenides, and the consequences for structure and properties. [1] Yamaura, J.-i.; Maki, S.; Honda, T.; Matsui, Y.; Noviyanto, A.; Otomo, T.; Abe, H.; Murakami, Y.; Ohashi, N., (2020), Chemical Communications 56, 1385-1388. [2] Vonrüti, N.; Aschauer, U., (2019), Journal of Materials Chemistry A 7, 15741-15748. [3] Charles, N.; Saballos, R. J.; Rondinelli, J. M., (2018), Chemistry of Materials 30, 3528-3537. [4] Zhang, R.; Senn, M. S.; Hayward, M. A., (2016), Chemistry of Materials 28, 8399-8406. [5] Giddings, A. T.; Scott, E. A. S.; Stennett, M. C.; Apperley, D. C.; Greaves, C.; Hyatt, N. C.; McCabe, E. E., (2021), Inorg. Chem. 60, 14105-14115.

Resume : The Aurivilius series of formula (Bi2O2)(An−1BnO3n+1) include perovskite slabs of variable thicknesses, n=1,2,3 … separated by Bi/O layers (where A is a large 12 coordinated cation, and B is a small 6 coordinated transition metals). They are generally limited to high oxidation state diamagnetic B cations such as Ti4+, Nb5+, W6+ . Due to the Bi3+ lone-pair effect, they mostly crystallize in polar space groups associated with attractive dielectric/ferroelectric properties. One way to access magnetically-active 3d transition metal oxide B ions is to partially substitute the O2- anionic sublattice by F - anions. Besides the limited number of reported Aurivilius (n=1) diamagnetic oxyfluorides such as Bi2Ti4+O4F2, Bi2Nb5+O5F, VBi2V 5+O5F the recent synthesis of Bi2Co2+O2F4 opens wide potentialities to combine ferrolectric and magnetic properties. We prepared Bi2M(O,F)6 (M=Fe2+, Ni2+, V4+) as single crystals and/or polycrystalline samples, returning informative data on their accurate crystal structures, the O/F ordering in supercell, the occurrence of various structural modulations … etc. The segregation of antagonist O2- and F- anions in distinct sub-units of the structure has a significant impact on the bandgap and electronic properties. Electric and magnetic properties will be presented through the prism of their possible coupling into multiferroics.

Resume : We report on the new Ruddlesden-Popper oxyfluoride La2NiO2.5F3 containing an unprecedented high amount of fluorine while preserving nickel in the oxidation state 2. The oxyfluoride was prepared from the corresponding oxide La2NiO4 in a topochemical low-temperature fluorination with poly(vinylidene fluoride) (PVDF) as fluorinating agent. The reaction proceeds via several reaction intermediates, which are additionally discussed. We found that La2NiO2.5F3 can only be prepared by fluorination of oxides from a citric acid assisted soft chemistry synthesis, while attempts using La2NiO4 from the classical mixed oxide methods were unsuccessful. Thermogravimetric analyses show that La2NiO2.5F3 already starts decomposing at 380°C, which is only slightly above the synthesis temperature of 370°C. In addition, even at 370°C reaction times longer than 12 h are disadvantageous as found by high-temperature powder x-ray diffraction. These might be the reasons why this oxyfluoride has not been discovered before. La2NiO2.5F3 is the first n = 1 Ruddlesden-Popper compound crystallizing in the tetragonal space group P42/nnm (a = 5.7297(6) Å; c = 13.0106(2) Å). The crystal structure shows a unique tilting scheme of the NiO4F2 octahedra that has so far been only theoretically predicted. Combined neutron and X-ray powder diffraction experiments together with Bond-Valence-Sum and DFT U calculations reveal an anion ordering with fluoride being located on the apical anion sites of the NiO4F2 octahedra. An unusual arrangement was observed for the excess fluorine ions, which were found to populate two of the four possible interstitial anion sites in an ordered fashion. A third interstitial anion position is occupied by oxygen ions while the fourth site remains unoccupied. This hitherto unobserved anion ordering scenario in Ruddlesden-Popper oxyfluorides is additionally supported by the volumes of the corresponding Voronoi-polyhedra und results from a pronounced layer-wise alternating tilting of the NiO4F2 octahedra. Magnetic measurements show strong antiferromagnetic interactions with an unusually high Néel temperature of about 225 K and a pronounced ZFC/FC splitting. Field-dependent hysteresis loops reveal the presence of a small unsaturated ordered moment. We propose the magnetic properties to result from an antiferromagnetic ordering with a slight spin canting. In contrast to the parent oxide La2NiO4 and a related compound La2NiO3F2, which are both black, our new oxyfluoride La2NiO2.5F3 is basically colorless. Determination of the optical band gap from the Kubelka-Munk transformed UV/Vis reflectance spectrum results in a value of 3.4 eV, which is much larger than the 1.3 eV of La2NiO4. DFT calculation using PBE U and Becke-Johnson functionals confirm this value and reveal an indirect band gap. In summary, our investigations demonstrate that low-temperature fluorination of Ruddlesden-Popper oxides can lead to interesting structural features and can also be used to modify the magnetic and optical properties of such materials.

Resume : Oxychalcogenides are, among the versatile mixed anion compounds [1], emerging as suitable alternative candidates for a variety of applications including for energy and environmental issues [2]. They have also been very recently emphasized as promising mid IR nonlinear optical (NLO) materials [3]. Indeed, it has been shown that functional groups composed of mixed anions may enhance the second harmonic generation (SHG) response through their greater acentric character. Through several structure types based on thiovanadates V(O,S)4 building blocks as well as new oxychalcogenides building blocks, we will discuss the possibility to tune the symmetry to reach highly polar structures and engineer the band gap. For instance, we have elaborated the thiovanadate-based compound Ba5(VO2S2)2(S2)2 [4] which exhibits third-harmonic generation properties. We have also opened new perspectives in the polar Fresnoite type family with new SHG active materials which will be discussed with support of DFT calculations [5]. In this context, we will present unprecedented oxysulfide building block for SHG active materials. New mixed anion Apatite phases will be also presented with emphasize on the effect of the mixed anion subarray on the photoconduction properties. References : [1] Kageyama, H. et al. Nature Communications 2018, 9 (1), 772. [2] Wang, Q. et al. Nat. Mater. 2019, 18 (8), 827–832. Kabbour, H. et al. Chem. Commun. 2020, 56 (11), 1645–1648. [3] Li, Y. Y. et al. Cryst. Growth Des. 2019, 19 (7), 4172–4192. [4] Almoussawi, B. et al. Inorganic Chemistry 2020, 59 (9), 5907–5917. [5] submitted (2022)

Resume : The ordering of anions with low Z can be hard to detect with bulk diffraction methods if the ordering is fragmented because of twinning, inhomogeneous modulations over the crystals, defects or any other type of domains. If large enough single crystals cannot be grown for single crystal X-ray or neutron diffraction, then the detection of anion order becomes even more difficult, as the often weak extra reflections can be hard to detect in the powder patterns. In such case electron diffraction has always been an obvious solution, as it already provides high quality single crystal patterns of crystals of mere nanometer sizes. It allowed to detect anion order and derive the corresponding supercell and symmetry. This is now being replaced by the quantitative form of three dimensional electron diffraction (3D ED), which allows to use the reflection intensities gathered from electron diffraction patterns as one might use those from X-ray or neutron diffraction patterns for solution and refinement of structures. There are also other advantages to 3D ED than merely the possibility to use nanometer size crystals, as electrons are more sensitive for light elements in the presence of heavy ones than X-rays and allow an easier detection of absolute configurations, for example. In this lecture we will show several cases where 3D ED has been crucial for the study of anion ordering, as well as pioneering experiments in in situ 3D ED where we change the anion content while following the structure evolution from 3D ED data acquired in situ during redox reactions. Both possibilities and current challenges will be discussed. Acknowledgements: Financial support is acknowledged from FWO I003218N, University of Antwerp BOF TOP 38689 and the European Commission NanED Grant number 956099.

Resume : The thermal conductivity of crystalline materials cannot be arbitrarily low, as the intrinsic limit depends on the phonon dispersion. We use complementary strategies to suppress the contribution of the longitudinal and transverse phonons to heat transport in layered materials containing different types of intrinsic chemical interface. BiOCl and Bi2O2Se encapsulate these design principles for longitudinal and transverse modes respectively, and the bulk superlattice material Bi4O4SeCl2 combines these effects by ordering both interface types within its unit cell to reach an extremely low thermal conductivity of 0.1 W.K-1m-1 at room temperature along its stacking direction1. This value comes within a factor of four of air. We demonstrate that chemical control of the spatial arrangement of distinct interfaces, through inclusion of multiple anion sublattices, can modify vibrational modes to minimize thermal conductivity. A related family of materials is also shown to exhibit similar properties. 1 Gibson, Quinn D., et al. "Low thermal conductivity in a modular inorganic material with bonding anisotropy and mismatch." Science 373.6558 (2021): 1017-1022.

Resume : Synthesis of Nanostructured Molybdenum Nitride and Carbide Catalysts Using Metal Cluster Compounds as Precursors: Application to the Hydrogen Evolution Reaction (HER). Transition metal carbides and nitrides show interesting properties in heterogeneous catalysis.1,2 Several authors report the use of Mo2C and Mo2N to catalyse the Hydrogen Evolution Reaction (HER).3,4 When synthesized by the urea route,5 Mo2C shows an electrocatalytic activity superior to that of other catalysts (Mo2N, and MoB) in acidic and basic aqueous media, although still inferior to that of platinum.6 Nevertheless, the use of Mo2C carbide would be an alternative to platinum that would make the technology more economically viable. Herein we report the synthesis of Mo2C and Mo5N6 from an original route which consists to use transition metal cluster-based precursors.7 The resulting carbides and nitrides are characterized by using several complementary techniques (XRD, SBET measurement, SEM, etc...). This innovative mode of synthesis affords nanostructured compounds that were evaluated as catalysts for the HER reaction both in acidic and basic conditions (respectively H2SO4 0.5M and KOH 0.1M). References: 1. Hargreaves, J.S.J. et al. Coord. Chem. Rev. 257, 2015–2031 (2013). 2. Wang, H. et al. Chem. Soc. Rev. 50, 1354–1390 (2021). 3. Kumar, R. et al. J. Mater. Chem. A 5, 7764–7768 (2017). 4. Jiang, R. et al. Electroch. Act. 261, 578–587 (2018). 5. Giordano, C. et al. Chem. Mater. 21, 5136–5144 (2009). 6. Ma, L. et al. Mater. Chem. A 3, 8361–8368 (2015). 7. Guy, K. et al. Chem. Mater. 32, 6026–6034 (2020).

Resume : Insertion of fluoride anions into oxide materials is an interesting way to modulate cation oxidation state,1 and increase covalency of the M-O bond thanks to the inductive effect procured by the highly electronegative F- anion. When applied to perovskite related oxides, which are known for the O2- conductivity and their use in solid oxide cells, this substitution can be exploited to improve electronic and oxygen conductivity as well as surface exchange properties,2 and in turns decrease operating temperature of devices. With this in mind, we have studied Ruddlesden-Popper oxyfluorides Srn+1(Fe,Co)nO3nFx, (0 < x < 1) ) which crystallize in a tetragonal unit cell (P4/nmm or I4/mmm). Synthesis conditions (gas atmosphere, applied pressure…), the number n in the series and the transition metal have a profound impact on the structure, with variation of the degree of anion site disorder, as well as on the effective cation oxidation state, and fluorine content.3–5 In particular, in Sr2FeO3F, fluorine and oxygen anions are ordered, forming alternating (SrF) and (SrO) rocksalt layers. Fe-F distance are considerably larger than Fe-O distances, so that Fe resides in a square pyramidal environment. Moreover, when synthesized under air atmosphere, Fe cations are partly oxidized leading to the non-stoichiometric Sr2FeIII0.8FeIV0.2O3.2F0.8 compound, as revealed by Mossbauer spectroscopy.5 This has a direct impact on the electronic conductivity, with the oxidized compound being a degenerated semiconductor, while the compound synthesized under air is an insulator. An in depth structural study combining synchrotron and neutron diffraction data with high resolution electron microscopy was performed which reveals the perfect ordering of F and O anions and highlight the presence of interesting structural defects. The substitution of Fe by Co cations was performed as a way to modulate the degree of anionic site disorder as well as cation oxidation states and oxygen overstoechiometry and thereby increase the electronic and ionic conductivity. Along with their structural investigation, compounds with different Co/Fe content were tested as air electrodes in symmetrical cells and the promising properties obtained pave the way to further improvement and exploration of oxyfluorides for this application. References 1. Harada, J. K., Charles, N., Poeppelmeier, K. R. & Rondinelli, J. M. Advanced Materials 31, 1805295 (2019). 2. Zhang, Z., Zhu, Y., Zhong, Y., Zhou, W. & Shao, Z. Advanced Energy Materials 7, 1700242 (2017). 3. Tsujimoto, Y., Matsushita, Y., Hayashi, N., Yamaura, K. & Uchikoshi, T. Crystal Growth & Design 14, 4278–4284 (2014). 4. Case, G. S. et al. Journal of Materials Chemistry 9, 2821–2827 (1999). 5. Galasso, F. & Darby, W. Journal of Physical Chemistry 67, 1451–& (1963).

Resume : Solid state chemistry is a well-researched topic around the whole world, conventionally, people use ceramic method to synthesis novel compounds. However, those compounds synthesised by this method are normally thermodynamically stable, the selection of the compounds are limited. In order to explore more novel solid-state compounds, a new synthesis method is needed. Reactions by low temperature topochemical manipulation has provided an alternative pathway to synthesize novel metastable chemical compounds with unusually low oxidation state and local coordination environments (e.g. Co1+, Ni1+, Ru2+, Ir2+ etc.) As this method utilises low temperature condition, the compounds synthesized are kinetically stable, which has allowed us to obtain metastable phases which cannot be done under the conventional method. During a topochemical reduction reaction, highly mobile atoms will be removed easily from the structural framework while keeping the heavy transition metal cation framework unchanged. By using different metal hydride reductants, O2- could be removed from the structure to form an oxygen deficient phase, or exchange by an H- to form a mixed anion oxyhydride compound. As H- only has 1s2 electronic configuration, it does not have π-symmetry valence orbitals, in another words, it does not form bond with the transition metal orbital that has π symmetry. This means that H- can act as a π blocker and block any type of interaction with the M t2g orbital, the effect has a bigger contrast when the anions are ordered. As seen in the ordered oxyhydride SrVO2H, metallic behaviour along the M-O plane was seen upon pressure, but not along the M-H apical direction as all d electrons are occupied at the t2g orbital. Furthermore, H- is more polarizabe and less electronegative than O2-. This means that M-H bonds formed would be more covalent than the M-O bonds. As a result, this could increase the magnetic exchange coupling and hence the magnetic ordering temperature as seen in LaSrCoO3H0.7. The structures and physical properties of some new reduced mixed 3d/4d transition metal oxyhydride and oxides phases will be presented.

Resume : Mixed anion compounds have received significant interest in recent years because of their promising application in various fields1. Oxychalcogenides are one class of mixed anion compounds related to very well studied oxide materials such as perovskites. Ae2MO2Cu2-δCh2 (Ae = Sr, Ba; M = 3d transition metal, Ch = S, Se, Te) are an interesting class of compound in the oxychalcogenide family showing diverse magnetic and electronic properties2. The example Sr2MnO2Cu1.5Se2 has a layered structure made of alternating Sr2MnO2 perovskite type layers containing Mn2+ and Mn3+ ions and Cu1.5Se2 anti-fluorite type layers3. In this study, we have utilized the high mobility of Cu in the metal chalcogenide layer of Sr2MnO2Cu1.5Se2 to replace it with similarly-sized Li in a soft chemical process. This has produced a new compound Sr2MnO2Li2Se2 with Mn2+ ions only, which has a different magnetic ordering scheme than the parent compound Sr2MnO2Cu1.5Se2. The structure and magnetic behaviour were characterized using synchrotron X-ray and neutron powder diffraction.

Resume : In this presentation, we report a new series of lithium/sodium-rich antiperovskites with chalcogenide divalent anion (Ch2– = S2–, Se2–, Te2–) sit at A-site and monovalent hydride (H–) or fluorine (F–) anion sit at B-site [1-2]. Except the orthorhombic Na3HS and Na3FS with distorted octahedra, the (Li/Na)3(H/F)Ch antiperovskites crystallized into the ideal cubic structure under high pressure. This unconventional robustness of cubic structure, particularly in the Li3HCh series exhibiting a wide range of tolerance factor (0.85 < t < 0.97), primarily comes from the large size-flexibility of the H– anion. The combined theoretical calculations and impedance measurements confirm the low Li+/Na+ migration barriers in these antiperovskites. To be more specific, the much stronger Li/Na–F bond strength than that of Li/Na–H does not impede the ionic motion, which indicates the role of long-range bonding interactions between chalcogenide anions and the moving ions. Comparative study between the hydride- and fluorine-based antiperovskites further reveals a relationship between the tolerance factor, the soft rotational phonon mode, and the migration barrier: the cubic antiperovskites with low t show a low frequency of the rotational mode and thereby a low migration barrier. Exemplary optimization through facile aliovalent doping of iodine are demonstrated in the Na3HSe and Li3FSe that exhibit high conductivities and low activation energies. References [1] Gao, S., Broux, T., Fujii, S. et al. Hydride-based antiperovskites with soft anionic sublattices as fast alkali ionic conductors. Nat Commun 12, 201 (2021). [2] Fujii, S. and Gao, S. et al. Alkali-rich antiperovskite M3FCh (M = Li, Na; Ch = S, Se, Te): The role of anions in phase stability and ionic transport. J. Am. Chem. Soc. 28, 10668–10675 (2021).

Resume : The continuous improvement of electrochemical technologies plays an important role in the transition to a society based on renewable energies. To this end, many electrolyzers are being synthesized to convert renewable electricity into value-added fuels and chemicals. In last decades, a major challenge is to develop catalysts with sufficient activity (e.g. minimal potential) to make economically competitive usable materials.(1) Much effort has been devoted to improving the activity of catalysts such as engineering their surface, composition or crystal structure. The conversion of waste biomass by electrochemistry is an appealing direction to generate high-value fuels and chemical under mild conditions. The electrochemical oxidation of 5-hydroxymethyl furfural (HMF) that is genuinely extracted from hexose and pentose sugars can be a study case as a biomass platform valorisation. HMF molecules can be oxidized to furandicarboxylic acid (FDCA), a promising building block for polymers and is set to compete with polyethylene terephthalate (PET)-based materials.(2) Within the catalyst used for such reaction, the tuning of inductive effects to modulate the electronic structure can have a big impact on the FDCA formation results. Phosphate based materials belong to the large polyanion compounds family containing a series of tetrahedron anion units [PO4]3– or their derivatives [PmO3m 1]n– with strong anionic network resulting in high chemical and thermal stabilities for long-time energy applications, making them ideal candidates as electrolyzers. Following this idea, two strategies were investigated. Firstly, the double substitution, cationic and anionic, of the copper phosphate Cu3(PO4)2 was studied. Obtained by high-energy ball-milling, Cu1.8Co0.2PO4F was characterized by a combination of electrochemical and spectroscopic techniques, to follow the HMF oxidation reaction (HMFOR). After 5.5 h, FDCA was generated with a final Faradaic efficiency of 95% and a yield of 85%.(3) This represents a significant improvement over pure cobalt-based catalysts often displaying less selectivity. Secondly, and to better understand the HMFOR mechanism, we investigate three different nickel phosphate materials with different Ni/P and thus, different anionic linkers : Ni3(PO4)2 with [PO4]3-, α-Ni2P2O7 with pyrophosphates [P2O7]4- and Ni2P4O12 with [P4O12]4- tetraphosphates (rings of four phosphates sharing corners). Interestingly, the HMFOR activity is related to the phosphate content and the results indicate that the synergy between proximal nickel and phosphate species is key to optimal HMFOR. Specifically, polyanionic unit nature plays a crucial role as hydrogen abstraction units, enabling the excellent performance of the phosphates investigated, especially for Ni2P4O12 (99% Faradaic efficiency and 95% product yeild). References 1 J. Carneiro, Ann. Rev. Chem. Biomol. Eng., 2019. 2 R.-J. van Putten, Chem. Rev., 2013. 3 K. Lemoine, Chem. Comm., 2020.

Resume : In the last 5 years, the optical photochromism of RE oxyhydride thin films has been extensively studied.[1] However, their large persistent photo-conductivity has been somewhat neglected. Here, we present an extensive characterization and demonstrate that photochromism and photo-conductivity originate from the same process, as indicated by a comparable time and temperature dependency, and by a unique exponential relation linking material conductivity and optical absorption. The reported photoconductivity does not find a simple explanation in the framework of the mechanisms proposed for the photochromism, namely (i) the reversible segregation of a metallic phase, and (ii) the reversible formation of a broad ensemble of optically-absorbing in-gap defects. Individually, neither of these mechanisms can account for the experimental photo-conductivity if not under counter-intuitive conditions at odds with previous works. Therefore, we propose that the hypotheses of metallic phase segregation (explaining the optical absorption) and defect formation in the RE oxyhydride matrix (explaining the increase of charge carriers) should be considered – together and simultaneously – in the framework of a single process initiated by the electron-hole formation. [1] G.Colombi et al., ACS Photonics 2021 8 (3), 709-715

Resume : Historically, the optimization of physical properties of oxides has mainly been realized by cationic substitutions leading to moderate chemical alterations (control of the valence states, control of the anionic vacancies…) while the anionic substitutions strongly impact the chemical bonding (iono-covalency, polarizability, geometry…).[1] For photocatalysis applications, the anionic mixing allows to finely control the photon absorption and electron-holes transport properties thanks to band gap and local symmetry engineering.[2,3] Although numerous derivatives exist, the pyrochlore A2B2X6X’ structure is often described as two interlocked sublattices, A2X’ and B2X6, with an anionic site, X’ (8b Wyckoff position of the Fd-3m space group, X’= O, N, F, S and/or □…), possessing a large versatility towards the anionic diversity while the X site (48f position, X= O, F or S) has very often been reported as mono-anionic.[4] During this talk, through several new oxysulfides A2B2O5S1□1 and oxyfluorides A2B2O5F2 (with A= Na+ and/or ½ Sn2+ and B= Nb5+ or Ta5+) characterized by powder XRD, solid state NMR (19F, 23Na and 119Sn) and DFT calculation, unusual anionic distributions will be addressed. [5,6] For instance, in Na2Ta2O5S1□1, as the large S2- occupy the X’ site, the vacancies are located in X site leaving Ta in an oxygen deficient environment never observed, in such an extent, for pyrochlore compounds. Furthermore, Na2Nb2O5F2 possesses fluorine in both X and X’ site giving rise to Nb in a mixed O/F environment. The Na+/Sn2+ cationic exchange, from Na2M2O5F2 (M=Nb, Ta), leads to new metastable phases, Na2-2xSnx□XM2O5F2, in which the unusual anionic distribution is preserved. Here, the Sn 5s² lone pair stereo-activity, the local Sn2+/Na+/□ ordering and the anionic mixing confer to these materials unprecedented crystallographic features as well as remarkable physical properties. Indeed, the stereo-active lone pair of Sn2+, located at the top of the valence band, massively reduces the band gap and hence promotes the visible light absorption which, in return, considerably enhances the photoconduction response and makes these materials suitable for overall water splitting photocatalysis under visible light irradiation. References: [1] Kageyama, H. et al. Nat. Commun. 2018, 9(772) 1-15. [2] Kabbour, H. et al. Chem. Commun. 2020, 3, 1645–1648. [3] Vonrüti, N. et al. J. Mater. Chem. A. 2019, 7, 15741–15748. [4] Talanov, M. V. et al. Chem. Mater. 2021, 33, 2706–2725. [5] Boivin, E. et al. Accepted in Chem. Comm. 2022 [6] Boivin, E. et al. Submitted in Chem. Mater. 2022

Resume : Transition metal oxides with perovskite structure have been widely used as a stage for generating various electronic properties, such as superconductivity and magnetism. By introducing other anions to them, their material variation can be further expanded and, moreover, novel electronic functionalities are expected to emerge with the mixing of anions. For example, long-range ordering of anions might cause ferroelectricity. Mixing of anions introduces disorder, and the disorder-driven electron localization is largely affected by external magnetic field, leading to colossal magneto-resistance. Introduced anions also modify the crystal field around the cations and trigger phase transition. Distortion of octahedral network associated with anion doping suppresses the carrier motion which is practically useful for enhancing the electrical insulation of ferro/para-electric materials. Here we present thin film growth approaches to control the structure and properties of mixed anion perovskites. Thin films of perovskite oxynitrides were directly grown via gas phase reactions, where nitrogen was activated by a radio frequency plasma source. This nitrogen plasma assisted technique enabled fine tuning of the anion composition by carefully adjusting the film growth parameters. We also employed topochemical methods to fabricate oxyfluoride and oxyhydride thin films using CaH2 and PVDF as hydrogen and fluorine sources, respectively. The role of anions on the unique properties of mixed-anion perovskites as mentioned above will be discussed with the aid of theoretical calculations.

Resume : Rare-earth oxyhydride thin films show a color-neutral, reversible photochromic effect at ambient conditions. The origin of photochromism is a topic of current investigations. The electronic structure and defect evolution of photochromic YHxOy and GdHxOy thin films deposited by magnetron sputtering was investigated by positron annihilation spectroscopy, in comparison with Y, YH1.9, Y2O3 and Gd, GdH1.9, Gd2O3 films. Doppler broadening positron annihilation spectroscopy (DB-PAS) shows very similar trends for the Y- and Gd-based systems upon incorporating hydrogen and oxygen in the anion sublattice, reflecting the variation in the electronic structure of the metal, metal hydride, semiconducting oxyhydride, and insulating oxide films. In-situ DB-PAS shows that the illumination leads to the irreversible formation of small vacancy clusters. This supports the conjecture that H- and/or O2- ions become mobile upon illumination, resulting in anion vacancies that may subsequently cluster with cation vacancies, whose presence in as-deposited films was revealed by positron annihilation lifetime spectroscopy. In addition, in some of the oxyhydride films, strikingly similar partially reversible shifts in the Doppler parameters are observed, that suggest the reversible formation of domains with reduced O:H composition ratio during illumination. This supports proposed mechanisms for the photochromic effect in these rare-earth oxyhydrides based on the formation of metallic-like nano-clusters.

Resume : The photocatalysis is more and more extended in environment and energy domains for the degradation of pollutants or for the production of green solar fuels and chemical products such as CO, CH4, H2. In principle, an ideal photocatalyst should possess: (1) a relatively small bandgap to effectively harvest visible solar energy; (2) a crystal structure that promotes high intrinsic carrier density, charge mobility, and a long charge lifetime; and (3) conduction (CB) /valence band (VB) potentials and surface properties that drive the reaction towards a preferable reaction pathway. However, designing this ideal photocatalyst continues to be a challenge. To overcome this problem, it could be very interesting to be able to adapt the CB and VB positions according to targeted specific redox potentials. Mixed anion materials are known to present tunable properties thanks to anion substitution and so represent a promising approach for photocatalyst development. Among the available synthesis methods, reactive sputtering is a particularly versatile technique to deposit thin films with a controlled composition by only tuning the injected gas mixture. Hence, very large range of oxynitride composition might be obtained by sputtering a pure tantalum target in different Ar/O2/N2 gas mixtures. Moreover, as a gas/solid synthesis technique, it is known to be environment-friendly method, widely used in industry and easy to scale up. In the present study, we show how the thin films composition can be varied thanks to this technique: from various tantalum nitrides, TaN, Ta3N5, to tantalum oxide, Ta2O5, via composition around the TaON the stoichiometric oxynitride. To understand the nature of these ternary materials, they were deeply investigated by RBS, XPS, FTIR, and XRD, and also by local method, such as the Pair Distribution Function technique. Films can be considered as randomly mixed compounds at very short scale (< few nm), where part of each phases can be finely tuned by the process parameters. This composition variation allows a control of the thin films optical properties, followed by UV-visible spectroscopy and spectroscopic ellipsometry. Indeed, the TaN film has a metallic behavior, absorbing with a Drude model in a large range of wavelength; while TaOxNy materials are semiconductor and Ta2O5 insulators. For the intermediate tantalum oxynitrides, we demonstrate, that the progressive anionic substitution of N by O atoms leads to a bandgap engineering with values ranging from 1.7 to 2.7 eV. Light absorption properties were then link to photocatalytic activities of these films. We more particularly investigate the photodegradation of methyl-orange into water. However, due to their band positions adapted to water reduction and oxidation, these ternary materials also appear promising for H2 production by water splitting.

Resume : Thin films of fcc rare-earth metal oxyhydrides (REH3-2xO2, RE = Sc, Y, Gd, Dy, Er) show a photochromic effect. Their transparency can be lowered by incident UV-light within minutes. The bleaching that occurs in the dark usually takes place on a longer time scale (hours). Although the mechanism behind this effect is unknown, in this work, we explore the factors that influence photochromism using neodymium oxyhydrides (NdH3-2xOx) which, until now, had never been characterized outside the stoichiometric NdHO composition. The O:H ratio of the films can be tuned by the sputtering deposition pressure, resulting in a series of films that span a range of band gap energies (1.91-2.61 eV), tetragonality (c/a = 0.973-1.005), and photochromic contrast (10-55%). We find that the photochromism also appears in these tetragonal films. Annealing them at a moderate temperature (87 C) significantly slows the rate of photochromic color switching. For example, comparing samples heated for 2 h and 30 h, the bleaching speed slowed by nearly 3x. This implies that the defect structure of the thin films is an essential ingredient for the reversibility of the photochromic effect. We use X-ray diffraction, positron annihilation spectroscopy, and aliovalent substitution of the cation to investigate which defects and structural properties are (not) important for the reversibility of the photochromic effect in neodymium oxyhydride thin films.

Resume : In addition to the “first generation” of nitrogen-based materials (nitrides, azides, diazenides, and pernitrides), there is the socalled “second generation” involving C-centered complex anions, for example the carbodiimide anion (or “divalent nitride”), for which the anionic dimensionality grows from zero to one. The next topological step consists of the planar, boomerang-shaped dicyanamide anion (or “monovalent nitride”), in addition to the likewise two-dimensional guanidinate anion. And yet, there should also be the tetrahedral ortho-nitrido carbonate, a three-dimensional complex anion never observed before. Finally, extended carbon-nitrogen networks (that is, beyond isolated complex anions) are possible as well. There are new synthetic and experimental findings, for example as regards bismuth carbodiimide, the heaviest and most sensitive carbodiimide known. Also, there are new data as regards the electrochemical performance of iron carbodiimide. With respect to materials design, first-principles structural searches predict the first hydrogen-free guanidinates TCN3 (T = V, Nb, Ta) and also ortho-nitrido carbonates T’2CN4 (T’ = Ti, Zr, Hf) being mechanically and dynamically stable at normal pressure. Ortho-nitrido carbonates will be more covalent compared to carbodiimides or guanidinates and are likely to excel in terms of photoelectrochemical water splitting and nonlinear optics. Eventually, iron dicyanamide has eluded structural characterization until recently but reveals interesting magnetism at low temperatures. Likewise, so-called melaminates, deprotonated salts of molecular melamine have now been firmly established by liquid-ammonia syntheses of the potassium and rubidium melaminate salts. Finally, several polymorphs of BeCN2 have been predicted of which at least one should be thermodynamically stable at standard conditions.

Resume : Water splitting photocatalysts are materials that enable hydrogen fuel generation from water by simple light irradiation. Mixed-anion compounds, such as oxynitrides, oxysulfides and oxyhalides are promising candidates because of their narrower band gap compared to typical oxides, allowing to exploit the solar spectrum to a larger extent. Some layered oxyhalides containing double fluorite Bi2O2 layers, such as Bi4NbO8X (X = Cl, Br),[1] are featured by their stability against self-oxidation, which is a problem for conventional mixed-anion compounds, because the O 2p orbitals of the Bi2O2 layers occupy the valence band maximum (VBM). More recently, Bi2MO4Cl (M = Y, La, Bi) with a triple fluorite Bi2MO4 layer was found to allow the control of the conduction band minimum (CBM) with the M cation.[2] These oxyhalides with double or triple fluorite layers show excellent oxygen-evolving photocatalytic activities for Z-scheme type water splitting under visible-light irradiation. In this work,[3] we report on the synthesis, structure, and photocatalytic property of Bi4BaO6Cl2 (I4/mmm) with alternating double (Bi2O2) and triple (Bi2BaO4) fluorite layers. Rietveld refinements based on the neutron powder diffraction revealed the presence of cation disorder between Bi2O2 and Bi2BaO4 layers. This double-triple system can be extended to include Bi4CaO6Cl2 and Bi4SrO6Cl2 with orthorhombic distortions and different degrees of cationic disorder. The band gap of Bi4AO6Cl2 can be tuned by the choice of A cation, and Bi4AO6Cl2 showed stable water-splitting photocatalysis in the presence of a sacrificial reagent. VBM and CBM in Bi4AO6Cl2 are found to locate in the triple and double layer, respectively, which may suppress electron-hole recombination. This unique band structure is difficult to achieve in conventional oxyhalides consisting only of double fluorite layers or triple fluorite layers. [1] Fujito H.; Kunioku H.; Kato D.; Suzuki H.; Higashi M.; Kageyama H.; Abe R. J. Am. Chem. Soc. 2016, 138, 8–11. [2] Nakada A.; Kato D.; Nelson R.; Takahira H.; Yabuuchi M.; Higashi M.; Suzuki H.; Kirsanova M.; Kakudou N.; Tassel C.; Yamamoto T.; Brown C. M.; Dronskowski R.; Saeki A.; Abakumov A.; Kageyama H.; Abe R. J. Am. Chem. Soc. 2021, 143, 2491–2499. [3] Zhong C.; Kato D.; Ogawa K.; Tassel C.; Izumi F.; Suzuki H.; Kawaguchi S.; Saito T.; Saeki A.; Abe R.; Kagyema H. Inorg. Chem. 2021, 60, 15667−15674.

Resume : Mixed anion compounds provide a rich chemistry that allow fine tuning of their properties. In particular, anionic substitution [1] is a powerful method to design band gap tuned photocatalysts. In this work, we study how it impacts the oxysulfide system LaOInS2, from both the structural and the properties point of view. Two synthesis pathways were reported yielding two different polymorphs: the thermodynamically stable one with non-layered α-phase structure via direct solid-state reaction [2,3] and the metastable layered polymorph using metathesis [4]. The α polymorph exhibits rare heteroleptic coordination around indium [3] (InS5O) with both O-2p and S-3p hybridization with indium states. We could obtain using exclusively direct synthesis a series of Se substituted α-LaOInS2-xSex (x=0, 0.1, 0.25, 0.5, 1.5) which adopt the alpha form or the layered form depending on the Se ratio and/or the heat treatment. All phases exhibit an interesting photocurrent response under visible light. Further investigation showed that while the selenium decreases the photocurrent response, the stabilization of the layered type increases it due to a better charge carrier separation and transfer related to the 2D character. When substituting α-LaOInS2 with selenium of greater ionic radii, we show that both α-polymorph and the layered polymorph can be obtained using direct synthesis. The chalcogenide substitution in α-LaOInS2 (band gap of 2.66 eV) achieved to narrow the band gap allowing higher participation of the visible light to the photocurrent. Previous work showed that the two pure oxysulfides polymorphs [3, 4] exhibit photocatalytic activity for both H2 and O2 evolution from water under visible light irradiation. It suggests that the new compounds that we will discuss in this communication, should be also good candidates which is comforted by their valence and conduction bands being well positioned for the water splitting reaction. More Briefly, we will also discuss the effect of substitution on the lanthanide site. 1. H. Kageyama, K. Hayashi, K. Maeda, J. P. Attfield, Z. Hiroi, J. M. Rondinelli, K. R. Poeppelmeier. Nature Communications (2018) 9, 772 2. H. Kabbour, L. Cario, Y. Moe¨lo and A. Meerschaut, J. Solid State Chem., (2004), 177, 1053–1059. 3. Kabbour, H., Sayede, A., Saitzek, S., Lefèvre, G., Cario, L., Trentesaux, M., & Roussel, P. Chemical Communications, 56(11), 1645–1648 (2020). 4. Miura, A., Oshima, T., Maeda, K., Mizuguchi, Y., Moriyoshi, C., Kuroiwa, Y., Meng, Y., Wen, X. D., Nagao, M., Higuchi, M., & Tadanaga, K. Journal of Materials Chemistry A, 5(27), 14270–14277( 2017).

Resume : Bismuth-based compounds have attracted significant interest in photocatalysis domain. Among them, pristine bismuth oxyhalides (BiOX, X= F, Cl, Br, I) have been widely studied in recent years due to their unique layered structure (PbFCl-type) and excellent physicochemical properties. Even though much progress in photocatalysis has been achieved over BiOX, they are mainly focused on BiOX (X= Cl, Br, I) and less attention on BiOF (and derivates). Thus, for a long time, fluorinated bismuth derivative compounds were not considered as interesting materials for photocatalytic applications. Last 7 years, our group is working on bismuth oxyfluorides based compounds for photocatalysis in powder form as well as in thin films obtained by reactive magnetron sputtering and demonstrate that BiOxFy may reach promising photocatalytic activities. In the first part of this talk, the photocatalytic performances of 2 composite systems with heterojunction (BiOCl:BiOF and TiO2:BiOF) will be presented. In each case, the existence of heterojunction between BiOF and BiOCl or TiO2 lead to a significant improvement of the photocatalytic performances. Thus, thanks its lamellar structure which induces an internal electric field, BiOF appears as a very efficient co-catalyst for the separation of the electron-hole pair photogenerated into BiOCl or TiO2. It is worth noting that the presence of oxygen vacancies, and the chemical composition of these mixtures are important parameters to optimize the photocatalytic performances of these compounds. In the second part of this talk, we will focus our presentation on the original synthesis of bismuth oxyfluoride films with thickness in the range 30-95 nm deposited by reactive magnetron sputtering. This was achieved by sputtering a bismuth target (99.99% purity) at room temperature under different mixtures of the reactive gases O2 and CF4 such that the total gas flow rate was constant. Therefore, this technique made it possible to tailor the composition of films mainly made of Bi2OO.5F2. The chemical composition was analyzed by XPS indicating the presence of O, F, Bi3+ and metallic Bi chemical state. This result indicates that it is possible to obtain by a one pot method films made of Bi2OO.5F2:Bi heterojunctions. The investigations of the optical properties reveal that the refractive index and band gap values of these materials strongly depend on the oxygen to fluorine ratio. The photocatalytic activity of oxyfluoride films were measured and compared with the relative powders. Thus, it was observed that metallic bismuth/bismuth oxyfluoride films were capable of improving the optical absorption in the visible range hence enhancing the photocatalytic properties. The presence of metallic bismuth plays an important role in improving the separation efficiency of the photogenerated electron-hole pairs. Finally, films were also tested as material for photoconversion of CO2 to CO showing interesting conversion efficiency with high selectivity.

Resume : Materials with the potential for photocatalytic water splitting include oxides, sulfides and oxysulfides. Whilst many oxides photocatalysts are stable and have relatively easy synthetic routes, many have band gaps too large for excitation by the visible part of the electromagnetic spectrum. Whilst sulfides typically have smaller band gaps, they do not always show the same stability as oxides. The mixed-anions materials oxysulfides offer a compromise with band gaps that can be tuned to match the visible spectrum.[1] This is highlighted by Y2Ti2O2S5 with proven stability and the stoichiometric production of O2 and H2 under visible light.[2] Anionic mixing has numerous advantages, in particular it is possible, to tune the band gap while introducing an heteroleptic environment associated to local distortion. The later is beneficial to enhance polarity and the built-in electrical field in the case of polar structures. Such internal electrical field is a promising strategy to enhance electron-holes separation and thus improve the photocatalytic activity. This advantage was highlighted by theoretical work (epitaxial samples) [3] [4] and we’re keen to investigate the role of polar heteroleptic coordination environments in oxysulfide photocatalysts. To explore the roles of the heteroleptic coordination environment and the presence of lone pair cations, our studies have focused on Sr6Cd2Sb6S7O10 which is built from SbO3, SbS5 (homoleptic coordination environments) and SbOS4 (heteroleptic) units containing the 5s2 Sb3+ cation. We combined photo-electrochemistry studies (photoconduction, photocatalysis) with density functional theory DFT calculations (electronic band structure, fat bands, charge carries’ effective masses) to fully understand the structure-properties relationship. In this communication, we present an efficient electrons-holes separation in this material and give a comprehensive analysis of the structure-properties relationship supported by DFT electronic structure calculations. We analyze the role of the mixed-anion entities and of the lone pairs in making this material suitable for overall water splitting photocatalysis under visible light irradiation. Preliminary results will be also discussed for other systems and the role of the polarity will be revisited. References [1] Kageyama, H. et al. Nat. Commun. 2018, 9 (772), 1-15. [2] a) Wang, Q. et al. Nat. Mater. 2019, 18 (8), 827–832. b) Miura, A. et al. J. Mater. Chem A. 2017, 5, 14270. c) Kabbour, H. et al. Chem. Commun., 2020, 56, 1645–1648. [3] Vonrüti, N. et al. Journal of Materials Chemistry A, 2019, 7(26), 15741–15748. [4] Vonrüti, N et al. The Journal of chemical physics, 2020, 152(2), 024701, 2020.

Resume : Vanadium phosphate positive electrode materials attract great interest in the field of Alkali-ion (Li, Na and K-ion) batteries due to their ability to store several electrons per transition metal. These multi-electron reactions (from V2+ to V5+) combined with the high voltage of corresponding redox couples (e.g., 4.0 V vs. Na+/Na for V3+/V4+ in Na3V2(PO4)2F3) could allow the achievement of the 1 kWh/kg milestone at the positive electrode level in Alkali-ion batteries. However, a massive divergence in the voltage reported for the V3+/V4+ and V4+/V5+ redox couples as a function of crystal structure is noticed. Moreover, vanadium phosphates that operate at high V3+/V4+ voltages are usually unable to reversibly exchange several electrons in a narrow enough voltage range. During this talk, through the review of redox mechanisms and structural evolutions occurring upon electrochemical operation of selected widely studied materials, we will identify the crystallographic origin of this trend: the distribution of PO4 groups around vanadium octahedra, that allows or prevents the formation of the vanadyl distortion (O---V4+=O or O---V5+=O). [1-6] While the vanadyl entity massively lowers the voltage of the V3+/V4+ and V4+/V5+ couples, it considerably improves the reversibility of these redox reactions. Therefore, anionic substitutions, mainly O2- by F-, have been identified as a strategy allowing for combining the beneficial effect of the vanadyl distortion on the reversibility with the high voltage of vanadium redox couples in fluorine rich environments. Acknowledgements The authors thank Région Nouvelle Aquitaine, Région Hauts de France, TIAMAT, the RS2E Network, the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) and the European Union’s Horizon 2020 research and innovation program under the Grant Agreements No. 646433-NAIADES and No. 875629-NAIMA. References 1. Boivin, E.; Chotard, J.-N.; Masquelier, C.; Croguennec, L., Towards Reversible High-Voltage Multi-Electron Reactions in Alkali-Ion Batteries Using Vanadium Phosphate Positive Electrode Materials. Molecules 2021, 26, 1428. 2. Boivin, E.; Iadecola, A.; Fauth, F.; Chotard, J.N.; Masquelier, C.; Croguennec, L. Redox Paradox of Vanadium in Tavorite LiVPO4F1-yOy. Chem. Mater. 2019, 31, 7367-7376. 3. Nguyen, L H.B.; Broux, T.; Sanz Camacho, P.; Denux, D.; Bourgeois, L.; Belin, S.; Iadecola, A.; Fauth, F.; Carlier, D.; Olchowka, J.; Masquelier, C.; Croguennec, L. Stability in water and electrochemical properties of the Na3V2(PO4)2F3 - Na3(VO)2(PO4)2F solid solution. Energy Storage Materials 2019, 20, 324-334. 4. Nguyen, L.H.B.; Iadecola, A.; Belin, S.; Olchowka, J.; Masquelier, C.; Carlier, D.; Croguennec, L. A Combined Operando Synchrotron X-ray Absorption Spectroscopy and First-Principles Density Functional Theory Study to Unravel the Vanadium Redox Paradox in the Na3V2(PO4)2F3 - Na3V2(PO4)2FO2 Compositions. J. Phys. Chem. C 2020, 124, 23511-23522. 5. B. Singh, Z. Wang, S. Park, G. S. Gautam, J.-N. Chotard, L. Croguennec, D. Carlier, A. K. Cheetham, C. Masquelier, P. Canepa, A Chemical Map of NaSiCON Electrode Materials for Sodium-ion Batteries. J. Mater. Chem. A 2021, 9, 281-292. 6. S. Park, J.-N. Chotard, D. Carlier, I. Moog, M. Courty, M. Duttine, F. Fauth, A. Iadecola, L. Croguennec, C. Masquelier, Crystal Structures and Local Environments of NASICON-Type Na3FeV(PO4)3 and Na4FeV(PO4)3 Positive Electrode Materials for Na-Ion Batteries. Chem. Mater. 2021, 33(13), 5355-5367.

Resume : Current technology used in electric vehicles could soon reach its physicochemical limit and alternative ‘next generation batteries’ are needed to increase energy density.1, 2 By replacing the liquid electrolyte with a solid, All Solid-State Batteries (ASSBs) could provide increased energy density1, 3 whilst addressing the safety concerns related to the use of current flammable liquid electrolytes.2, 4 The discovery of novel solid electrolyte materials with lithium ion conductivities suitable for application remains one of the main challenges in the commercialisation of ASSBs. Recently, argyrodite and anti-perovskite materials have attracted attention displaying superionic conductivity, e.g. Li6PS5Br (6.8*10-3 S cm-1)5 and Li3OCl0.5Br0.5 (1.94*10-3 S cm-1).6 This work establishes a structural connection between the argyrodite and anti-perovskite material families. The ordered cubic argyrodite structure (F-43m) is usually described in terms of close packed tetrahedra or lithium ion cages surrounding the anions, however it can also be described as a defect (ABX3) anti-perovskite. From the existence of both cubic and hexagonal inverse perovskites we identify the potential for Li containing hexagonal argyrodites. Structures were built with compositions following Li6SiO4XX’ (X, X’ = F, Cl, Br, I) and following DFT and normal mode calculations several targets were identified for experimental synthesis, namely Li6SiO4Cl2-xBrx. Guided by computation, a new compound, Li6SiO4Cl2, was synthesised which is structurally related to both hexagonal argyrodite and hexagonal inverse perovskite. The new compound adopts an orthorhombic structure at room temperature and undergoes a phase transition to a hexagonal polymorph upon heating. This phase transition introduces lithium site disorder which is linked to an increase in lithium ion conductivity and a lowering in activation energy as observed by AC impedance and 7Li NMR spectroscopy. The Li site disorder observed in the hexagonal phase is analogous to that in cubic sulphide argyrodites (i.e. Li6PS5Br)5 which is known to be one of the mechanisms for superionic conductivity. In contrast, this disorder is absent in cubic Li6PO5Br7 where lithium ions remain localised over a wide temperature range leading to higher activation energies to bulk ion transport when compared to this new hexagonal argyrodite. References 1. T. Famprikis, P. Canepa, J. A. Dawson, M. S. Islam and C. Masquelier, Nat. Mater., 2019, 1-14. 2. J. Janek and W. G. Zeier, Nat. Energy, 2016, 1, 1-4. 3. D. Lin, Y. Liu and Y. Cui, Nat. Nanotechnol., 2017, 12, 194. 4. J. Li, C. Ma, M. Chi, C. Liang and N. J. Dudney, Adv. Energy Mater., 2015, 5, 1401408. 5. R. P. Rao and S. Adams, Phys. Status Solidi A, 2011, 208, 1804-1807. 6. Y. Zhao and L. L. Daemen, J. Am. Chem. Soc., 2012, 134, 15042-15047. 7. S. T. Kong, H. J. Deiseroth, J. Maier, V. Nickel, K. Weichert and C. Reiner, Z. Anorg. Allg. Chem., 2010, 636, 1920-1924.

Resume : KVPO4F and KVOPO4 (KTiOPO4-type structure) have recently been reported as high energy density (> 500 Wh·kg-1) positive electrode materials for K-ion batteries. With the aim of tailoring the properties of these materials, we synthesised mixed anion compounds KVPO4FyO1-y with y = 0, 0.25, 0.5, 0.75, 1 and determined their long distance structure with X-ray diffraction, local vanadium environment with EXAFS as well as their electronic structure with 31P MAS-NMR. The results of these characterisations evidenced the formation of an anionic solid solution across the whole composition domain. The simultaneous presence of V3 and {V=O}2 environment in anion mixed samples strongly influences the electrochemical properties. Further characterisation such as operando X-ray absorption spectroscopy at V K edge was performed and unveiled a complex redox mechanism during the charge and discharge of the battery. While the strong covalency of vanadyl entities was expected to lower the average redox potential of the oxygenated materials (as observed in analogous Li and Na compounds), a 250 mV increase in the electrochemical potential was observed upon full oxygenation. We will discuss this surprising behaviour based on the structural peculiarities of the KVPO4FyO1-y framework compared to Tavorite LiVPO4F1-yOy and Na3V2(PO4)2F3-2yO2y structures.

Resume : Closo-borane materials are currently amongst the top candidates for next generation Li solid state electrolytes. This is a result of them exhibiting high lithium ion conductivity of approximately 10-2 S cm-1, improved from 10-7 S cm-1 following and order-disorder phase transitions from orthorhombic to cubic symmetry at high temperature. Stabilization of the disordered, high conductivity structures at room temperature is required to enable these materials to be competitive with liquid electrolytes. Disorder in these materials is introduced in one of two ways: extrinsically (via ball milling) or intrinsically (through ion substitution within the structure).[1–5] Often, these two methods are used simultaneously through mechanosynthesis. Mechanosynthesis can limit the structural characterization, however formation of mixed-ion clusters via conventional solid-state synthesis leads to highly crystalline materials and, as a result, enables accurate characterization and understanding of the mechanisms that lead to high ionic conductivities. We report the successful synthesis and discovery of a new material based on a combination of the closo-carborane with a secondary anion. Analysis of powder X-ray diffraction data shows a new material and full structural analysis reveals a structure with hexagonal close-packing of anions with P63/mmc symmetry. Spectroscopic methods such as IR, Raman spectroscopy and NMR are utilized to understand how intrinsic disorder affects the materials performance. This new hexagonal material exhibits a stabilization of structural disorder resulting in enhanced ionic conductivity of 1.04 × 10-4 S cm-1 at room temperature. These results provide important thermodynamic and mechanistic insights that are informative to the future design of closo-borane based solid electrolyte materials. 1 W. S. Tang, A. Unemoto, W. Zhou, V. Stavila, M. Matsuo, H. Wu, S. Orimo and T. J. Udovic, Energy Environ. Sci., 2015, 8, 3637–3645. 2 L. Duchêne, R.-S. Kühnel, D. Rentsch, A. Remhof, H. Hagemann and C. Battaglia, Chem. Commun., 2017, 53, 4195–4198. 3 S. Kim, H. Oguchi, N. Toyama, T. Sato, S. Takagi, T. Otomo, D. Arunkumar, N. Kuwata, J. Kawamura and S. Orimo, Nat. Commun., 2019, 10, 1081. 4 W. S. Tang, K. Yoshida, A. V Soloninin, R. V Skoryunov, O. A. Babanova, A. V Skripov, M. Dimitrievska, V. Stavila, S. Orimo and T. J. Udovic, ACS Energy Lett., 2016, 1, 659–664. 5 Y. Sadikin, R. V Skoryunov, O. A. Babanova, A. V Soloninin, Z. Lodziana, M. Brighi, A. V Skripov and R. Černý, J. Phys. Chem. C, 2017, 121, 5503–5514.

Resume : The introduction of nitrogen in transition metal oxides involves changes in the electronic structure affecting the physical properties. The lower electronegativity and higher polarizability of nitrogen compared to oxygen increases the bond covalency decreasing the interelectronic repulsion. [1, 2] The larger electrical charge of nitride anion increases the crystal field splitting and the polarization, and allows the stabilization of structures with new cation compositions and properties. Because nitrides are less stable than oxides, the development of new synthetic approaches is necessary for the search of new compounds. This lecture will present different aspects of our recent research on nitride-based transition metal compounds focussing on the relationships between the synthesis conditions, the oxidation states of the cations, the ordering of anions and the electronic properties. LaTaON2 is a highly nitrided perovskite that shows a centrosymmetric, pseudocubic structure derived from the Pm-3m aristotype. A new preparation method at high temperature in N2 produces samples with enhanced grain growth and sintering that show a large dielectric permittivity, ascribed to partial, local order of N3- and O2- induced by covalency. The anion order in this compound, that has been also prepared by ammonolysis, has been found to be dependent on the synthetic approach. [3] The topotactic nitridation of cation ordered, tetragonal Sr2FeMoO6 in NH3 at moderate temperatures leads to cubic, Fm-3m double perovskite oxynitride Sr2FeMoO4.9N1.1 with high cation order, that shows ferromagnetic order and negative magnetoresistance below c.a. 100 K. [4] BaWON2 is the first example of a hexagonal perovskite oxynitride, resulting from the combination of a large A-site cation and the stabilization of the small W6+ to compensate the charge of the two nitride anions. [5] It crystallizes in the 6H polytype, in the non-centrosymmetric space group P63mc, and the anions N3- and O2- are completely ordered in the vertex shared and face shared positions, respectively, of the WX6 octahedra. The anion order, together with second order Jahn-Teller effect of W6+ cations and electrostatic repulsions along the sharing faces of the octahedra, induce high distortions in the coordination polyhedra leading a polar structure, and a large dielectric permittivity is observed. References [1] A.Fuertes, Mater. Hor. 2015, 2, 453. [2] A.Fuertes, APL Mater. 2020, 8, 020903. [3] A.Castets, I.Fina, J.R.Guarín, J.Oró-Solé, C.Frontera, C.Ritter, J. Fontcuberta, A.Fuertes, Inorg. Chem. 2021, 60,16484. [4] R. Ceravola, C. Frontera, J. Oró-Solé, A. P. Black, C. Ritter, I. Mata, E. Molins, J. Fontcuberta, A. Fuertes, Chem. Commun. 2019, 55, 3105. [5] J. Oró-Solé, I.Fina, C.Frontera, J.Gázquez, C.Ritter, M.Cunquero, P. Loza-Alvarez, S.Conejeros, P.Alemany, E.Canadell, J.Fontcuberta, A.Fuertes, Angew. Chem. Int. Ed. 2020, 59, 18395.

Resume : Transition metal nitrides (TMN) and carbides (TMC) have demonstrated interesting properties in heterogeneous catalysis in reactions traditionally catalyzed by noble metals [1]. They are often considered as platinoids for their close electronic properties. TMN and TMC contribute to the renewed interest in finding alternatives to these very expensive and rare noble metals (Pt, …) listed as critical raw materials. Our work aims at developing innovative syntheses to prepare nanostructured molybdenum-based catalysts from metallic clusters [2]. The nitridation of the nanometric precursor (TBA)2Mo6Br14 leads at relatively low temperatures to Mo2N and Mo5N6 nitrides with high specific surface areas. A similar approach between molybdenum clusters and sucrose or urea allows to extend this original process to the synthesis of nanostructured carbides. The presentation will be illustrated by results related to the water-gas shift reaction [3]. References: [1] Hargreaves J.S.J., Coord. Chem. Rev. 2013, 257, 2015-2031. [2] Kirakci K., Cordier S., Perrin C., Z. Anorg. Allg. Chem. 2005, 631, 411-416. [3] Guy K., Tessier F., Kaper H., Grasset F., Dumait N., Demange V., Nishio M., Matsushita Y., Matsui Y., Takei T., Lechevalier D., Tardivat C., Uchikoshi T., Ohashi N., Cordier S. Chem. Mater. 2020, 32, 6026-6034

Resume : Efficient catalysts are required for both oxidative and reductive reactions of hydrogen and oxygen in sustainable energy storage and conversion technologies, which has become a key requirement to satisfy rising global energy demand.[1] In a number of cases, the catalytic performance of nitrides is analogous with that of noble metals,[2] due to their very similar Fermi energy and electronic structure to that of group VIII noble metals,[3] but their activity mechanisms are unclear. Urea-glass route is employed to synthesize a ternary nitride Ni2Mo3N[4] which is found to be an outstanding oxygen evolution reaction (OER) catalyst that outperforms the benchmark material RuO2. Ni2Mo3N exhibits a current density of 10 mA cm-2 at a nominal overpotential of 270 mV in 0.1 M KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the surface electronic structure of active Ni-sites and Mo electron pumps in the discovered surface oxide-rich activation layer. Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen-containing species and facilitate the continuity of the reactions. Similarly, porous Co3Mo3N[5] prepared via a facile method is found to be an efficient and reliable multifunctional electrocatalyst for three essential energy conversion reactions; OER, oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in alkaline solutions. In practical demonstrations, Co3Mo3N gives high specific capacity (850 mA h gZn-1 at 10 mA cm-2) as the cathode in a zinc-air battery, and a low potential (1.63 V at 10 mA cm-2) using in a water-splitting electrolyzer. Availability of Co and Mo d-states appear to result in high ORR and HER performance, while the OER properties result from a cobalt oxide-rich activation surface layer. Acknowledgements: Financial support from Natural Science Foundation of China (Grant No. 21471147), National Key Research and Development Plan (Grant No. 2016YFB0101205), Hong Kong Research Grants Council through the Early Career Scheme (project No. 25301617), Ningbo 3315 program, EPSRC and American Chemical Society Petroleum Research Fund is acknowledged. References [1] Z. W. Seh, et al, Science 2017, 355(6321): eaad4998. [2] J. Xie and Y. Xie, Chemistry?A European Journal 2016, 22(11): 3588-3598. [3] D. J. Ham and J. S. Lee, Energies 2009, 2(4): 873-899. [4] Y. Yuan, et al, Angewandte Chemie International Edition 2020, 59(41): 18036-18041. [5] Y. Yuan, et al, The Innovation 2021, 2(2): 100096.

Resume : Heteroanionic compounds have emerged as a new materials platform to discover new functionalities.[1,2] An anionic sublattice populated by more than one anion specie, can include different chemistries such as chalcogenide (O, Se, S), halide (F, Cl, Br, and I), nitride or hydride, featuring distinct characteristics spanning charge, ionic radius, polarizability and electronegativities. Associating oxides, for which numerous inorganic compounds have been reported, with other anions offers an infinite set of possibility in terms of materials design and functions. Such a possibility can be exemplified for the oxyfluoride family with over 1000 compounds[1] available in the ICSD database and applicative outcomes in many fields that are optics,[3] or energy storage[4] to name a few. Solving the crystal structure of oxyfluorinated compounds is not often trivial as the distribution of oxide and fluoride over the anionic sublattice can occur in different degree of order-disorder. Oxide and fluoride anions have very similar X-ray and neutron scattering factors so that they can only be distinguished if arranged in a well-ordered crystal structure. In this case, bond valence sum[5] (BVS) or the Pauling’s second crystal rule[6] can be used to assign anions to crystallographic sites. In this presentation, we will discuss how fluoride and oxide anions arrange in different types of inorganic frameworks spanning the fluoride-substituting anatase[7] (TiO2) and two oxide-fluoride compounds (TiOF2) having the ReO3 and hexagonal-tungsten-bronze type structures[8,9]. The latter framework will be thoroughly discussed highlighting the challenge in describing the structural features occurring at different length scales. This work will shed light on the complementary use of local probes such as the pair distribution function, 19F NMR as well as DFT-calculations. References [1] H. Kageyama, K. Hayashi, K. Maeda, J. P. Attfield, Z. Hiroi, J. M. Rondinelli, K. R. Poeppelmeier, Nature Communications 2018, 9, 772. [2] J. K. Harada, N. Charles, K. R. Poeppelmeier, J. M. Rondinelli, Advanced Materials n.d., 0, 1805295. [3] H. Yu, M. L. Nisbet, K. R. Poeppelmeier, J. Am. Chem. Soc. 2018, 140, 8868–8876. [4] R. J. Clément, Z. Lun, G. Ceder, Energy Environ. Sci. 2020, 13, 345–373. [5] I. D. Brown, Chem. Rev. 2009, 109, 6858–6919. [6] A. Fuertes, Inorg. Chem. 2006, 45, 9640–9642. [7] W. Li, D. Corradini, M. Body, C. Legein, M. Salanne, J. Ma, K. W. Chapman, P. J. Chupas, A.-L. Rollet, C. Julien, K. Zhagib, M. Duttine, A. Demourgues, H. Groult, D. Dambournet, Chem. Mater. 2015, 27, 5014–5019. [8] A. Demourgues, N. Penin, E. Durand, F. Weill, D. Dambournet, N. Viadere, A. Tressaud, Chem. Mater. 2009, 21, 1275–1283. [9] A. Demourgues, N. Penin, D. Dambournet, R. Clarenc, A. Tressaud, E. Durand, Journal of Fluorine Chemistry 2012, 134, 35–43.