ANIM 3: advances and enhanced functionalities of anion-controlled new inorganic materials

Resume : Layered perovskite titanium oxyhydrides have been prepared by low temperature topochemical CaH2 reduction from Ruddlesden-Popper Srn+1TinO3n+1 phases (n = 1, 2) and structurally characterized by combined synchrotron X-ray and neutron diffraction data refinements. In the single-layered Sr2TiO3.91(2)D0.14(1) material, hydride anions are statistically disordered with oxides on the apical site only, as opposed to known transition metal oxyhydrides exhibiting a preferred occupation of the equatorial site. This unprecedented site selectivity of H- has been reproduced by periodic DFT+U calculations, emphasizing for the hydride defect a difference in formation energy of 0.24 eV between equatorial and apical sites. In terms of electronic structure, the model system Sr2TiO3.875H0.125 is found slightly metallic and the released electron remains mostly delocalized over several Ti atoms. On the other hand, hydride anions in the double-layered Sr3Ti2O6.20H0.12 material show a clear preference for the bridging apical site within the perovskite slabs, as confirmed by DFT calculations on the Sr3Ti2O6.875H0.125 model system. Finally, the influence of the B-site chemical nature on the hydride site selectivity for early 3d transition metals is theoretically explored in the single-layered system by substituting vanadium for titanium. The V3+ electronic polaron is suggested to play a role in stabilizing H- on the equatorial site in Sr2VO4-xHx for x = 0.125.

Resume : Due to the large difference in electronegativity the nature of hydrogen in Rare Earth hydrides (REHx) is anionic. This results in a metal/insulator transition at a critical metal/hydrogen ratio of around 2.7. Recently it was found that upon exposure to air, porous YH2 (and REH2) films transform into a photochromic oxyhydride state [1,2]. By a combination of Rutherford backscattering and elastic recoil detection, we found that the photochromic nature is maintained over a wide compositional range described by the formula REO(x)H(3-2x) where 0.5 < x < 1.5. This implies that the Y/RE cation maintains the 3+ valence for all photochromic compositions. Moreover, it can be clearly distinguished from the non-photochromic hydroxides. We propose a corresponding structure model based on an fcc-unit cell where the O2- and H- anions partially occupy the tetrahedral and octahedral interstitial sites. [3]. Our understanding of the photochromic properties is still limited. The optical excitation is clearly related to the bandgap, which varies with the O/H-ratio. Illumination induces a color neutral darkening over a wide wavelength range (from UV to mid-IR). We will discuss the physical mechanism of this effect based on recent data on the local structure obtained with EXAFS and muSR. References: [1] Mongstad et al., Solar Energy Materials & Solar Cells 95 (2011) 3596?3599 [2] F.Nafezarefi et al., Appl. Phys. Lett. 111, (2017) 103903 [3] S. Cornelius et al., J.Phys.Chem.Lett., submitted

Resume : Sevier reduction processes using metal hydride agents modify the chemical and structural properties of metal oxide crystals with different manners, depending on the host crystals and the process conditions. For example, the reduction of SrFeO3 preferentially eliminates O2- at axial sites in the FeO6 octahedra to convert to SrFeO2 with a planner four-coordinated Fe2+. This is regarded as the oxygen vacancy formation with trans-configuration in the octahedra. Herein, we focus on the metal hydride-reduction of BaSn1-xYxO3-x/2 with the primitive cubic perovskite structure and relevant defect chemistry. The sample color changed from white to yellow, red, and brown with keeping the cubic perovskite structure as the reduction proceeds. Partial reduction of Sn4+ to Sn2+ was observed by XPS. Chemical composition of a reduced sample with x = 0.3 was determined to be BaSn(IV)0.50Sn(II)0.20Y0.30O2.61H0.08 by Rietveld analysis of neutron diffraction data, implying that H- ion on the order of 10^21 cm-3 is incorporated in this sample. Moreover, high concentration of Sn2+ with a few tens of percent is formed. 119Sn Mössbauer spectra was analyzed by a DFT calculation of crystal models with oxygen vacancies, and revealed that 5s2 lone pair electronic states of Sn2+ is formed in the band gap above the valence band, and its electronic transition to the conduction band is responsible for the coloration. This defect is stabilized by oxygen vacancy pair with cis-configuration around the Sn2+

Resume : A layered oxychloride Bi4NbO8Cl is a visible-light catalyst for water splitting, with its remarkable stability ascribed to the highly dispersive O-2p orbitals in the valence band, but the origin of unique band structure remains unclear. We systematically investigate four series of layered bismuth oxyhalides, BiOX (X = Cl, Br, I), Bi4NbO8X (X = Cl, Br), Bi2GdO4X (X = Cl, Br) and SrBiO2X (X = Cl, Br, I) and found that Madelung site potentials of anions capture essential features of the valence band structures of these materials. The oxygen anion in the fluorite-like blocks (e.g. [Bi2O2] slab in Bi4NbO8C) is responsible for the upward shift in the valence band maximum, and the degree of electrostatic destabilization changes depending on building layers and their stacking sequence. This study suggests that the Madelung analysis enables a rough prediction or design of the valence band structures of bismuth and other layered semiconductors and is applicable even to a compound where DFT calculation is difficult to carry out. Bi 6s electrons also play an important role for elevating valence band maximum.

Resume : The compounds containing multiple anions in a single phase is so-called mixed anion-compounds, and have been considered as a new frontier of inorganic materials. One of the advantages of the compounds are the formation of the specific structures such as layered as well as the properties originated from the structure. Recently we developed a series of layered compounds composed by semiconducting metal-chalcogenide layers and insulating oxide layers such as Sr2ScAgSeO3[1]. These compounds show sharp exciton emission peaks near the band edge, and the stability of excitons at room temperature because of quantum confinement effect owing to their layered structure. The special feature of the system is the controllability of both combination of the elements and the stacking structures. These flexibility of the system offers to tune the band gap of the compounds, and structural difference gives different level of the quantum confinement effect as well as temperature stability of the luminescence. The chemical and structural flexibility of the layered structure has offered vast opportunities to raise the novel functionality of the materials. References: [1] Y. Iwasa, H. Ogino et al., Opt. Mater. 84 (2018) 205

Resume : Compared to conventional host materials, hydride and hydride-based mixed-anion compounds are expected to produce larger centroid shifts due to nephelauxetic effect induced by hydride ligands. However, their poor stability in air and moisture limits their application. In the present study, we investigated the photoluminescence properties of air- stable oxyhydride Sr2LiSiO4H doped with Eu2+ and Ce3+. The Eu- and Ce-doped phosphors were synthesized by solid state reaction of oxide and hydride precursors under H2 atmosphere. Both compounds exhibit the shifting of excitation and emission bands into longer wavelength region than those in the oxyfluoride analogue Sr2LiSiO4F:RE (RE = Eu2+ ,Ce3+) and show the yellow and green luminescence under near-UV light of 375 nm, respectively. The red-shifts induced by F- to H- substitution are consistent with the results of constrained density functional theory calculations predicting the photo-excitation and emission energies of 4f?5d transitions. These results demonstrate that the substitution of H- to F- sites in oxyfluoride-based phosphor materials is a promising strategy to create novel phosphor materials which can be excited by near-UV LED.

Resume : Polarity, for example in ferroelectric materials, can significantly increase a catalyst?s performance by improving charge-carrier separation. For photocatalytic water-splitting perovskite oxynitrides are promising materials due to their small band gaps as well as their suitable band edges that straddle the oxygen and hydrogen evolution potentials. Ferroelectricity can be induced by epitaxial strain in these materials. However, polar distortions also increase the band gap as was shown for epitaxially strained SrTiO3 [1]. While this band-gap increase is small for oxides, our density functional theory calculations show a much larger increase for oxynitrides: The enhanced covalency due to reduced electronegativity of nitrogen compared to oxygen results in larger strain-induced polar distortions and therefore more strongly increased band gaps by up to 1.5 eV. The reduced electronegativity, which leads to a higher valence band in oxynitrides and therefore a band gap in the visible that is attractive for photocatalysis, thus also has a detrimental effect on photo absorption when polar distortions are present. This results in a trade-off between small band gaps and polarity. We will discuss different strategies on how to overcome this trade-off with mixed anion perovskite compounds, such as oxysulfides and oxyhydrides, which have not yet been considered for photocatalytic water-splitting. References: [1] RF Berger et al. PRL 107.14(2011):146804

Resume : Layered transition metal compounds have been extensively investigated due to their unconventional electronic/magnetic properties. Topochemical reactions, which introduce/withdraw ions into/from host materials retaining their lamellar structures, serve as one of the most effective tools to design such low-dimensional materials. Despite their huge advances during the recent decade, most of topochemical reactions rely on redox activities of transition metal cations in host lattices so that their charge balance are respected throughout the process. Conversely the redox activity of molecular anions for topochemical syntheses remains almost unexplored. We demonstrate here that electron transfer from Cu0 to chalcogen dimers (Q2)2- (Q = S, Se) and concomitant Q-Q bond cleavage enable host lattices to accommodate Cu+ cations, yielding extended (CuQ) sheets [1]. This concept is verified on various (Q2)2--containing materials with different cationic layers and chalcogen species. The general applicability of the concept beyond the reaction between dimer and copper will be also discussed. References: [1] S. Sasaki, D. Driss, E. Grange, J.-Y. Mevellec, M. T. Caldes, C. G.-Deudon, S. Cadars, B. Corraze, E. Janod, S. Jobic, L. Cario, Angew. Chem. Int. Ed., 57, 13618-13623 (2018).

Resume : Pressure has been extensively used to synthesize new materials, induce phase transitions and control properties in many inorganic compounds [1]. However, few studies have been carried out on the effects of pressure on the electronic and structural properties in oxyfluorides using first-principles methods. By combining density functional calculations and high-pressure Raman spectroscopy, we efficiently search for previously unknown phases predicted from theory and assess the structures experimentally. We used this methodology to study the pressure (0-10 GPa) effects on the experimentally known non-centrosymmetric phase of KNaNbOF¬5 [2]. We predict that as pressure is increased, this material undergoes an isostructural phase transition with concurrent changes in its electronic structure [3]. We explain these variations in the electronic properties as arising from variations in local chemical bonding. References: [1] L. Zhang, et al., Nat. Rev. Mat. 2, 17005 (2017) [2] M. Marvel, et al., J. Am. Chem. Soc. 129, 13963 (2007) [3] A G. Christy, Acta Cryst. B51, 753-757 (1995)

Resume : The anion order in perovskite oxynitride materials presents an additional degree of freedom to tune the material’s properties. We have previously shown, based on density functional theory (DFT) calculations, that the anion order at the surface is different from the one in the bulk for LaTiO2N. Here we assess the thickness of this trans ordered surface layer and show how it affects the catalytic activity towards water oxidation. We also discuss peculiarities of the defect chemistry of oxynitride surfaces in a catalytic setup and the effect of defects on the catalytic activity. Finally, we show how new electronic functionality analogous to the celebrated LaAlO3/SrTiO3 interface may result from modulated anion order in oxynitride materials.

Resume : The search for new phases with original properties is a major task in inorganic chemistry. Mixed anion compounds have proved their importance at this level and provide a rich chemistry to tune the properties. In the oxychalcogenides family for instance, LaOCuCh (Ch= chalcogenide) based systems are wide band gap semiconductors [1] and doped La2O2S provide inorganic phosphor materials [2].The main purpose of this work is to synthesize new mixed anion phases with innovative physical and chemical properties with emphasize on their potential optical properties. The idea is to draw on structural entities with mixed anions to formulate new phases with multiple advantages related to these characteristics (modulation of properties, strongly acentric entities with exacerbation of some properties...). Compounds such as Ba2In2Si3O10S or Ba2SiS5 inspired us for anionic modifications. The former exhibits a layered structure, and the later disconnected tetrahedra while both have large optical gaps [3]. It is interesting to mention BaGeOSe2 because it exhibits acentric mixed anion entities GeO2Se2 that lead to enhanced NLO properties compared to the analogue oxide [4]. In this work, the mixed anion compound with the formula Ba6SiInSe9I was successfully synthesized. The structure is composed of mixed tetrahedra Si4+/In3+ cations coordinated by selenide anions. Mixed Se2-/I- sites are found in the vicinity of Ba2+ cations. The structure . We will also discuss other original phases obtained during our prospection such as Ba2ZnInS4 that exhibits a 3D framework with isolated tetrahedra. The crystal structures will be correlated to the properties with support of DFT calculations, in particular the mixed anion bonding will be emphasized. References: [1] Unrevealed electronic and optical properties of the layered oxychalcogenides (LaO)CuCh (ch=S, Se, Te): A density-functional study. al., M.Shibghatullah et. s.l. : Japanese journal of applies physics, 2017, Vol. 56. [2] Vertex-linked ZnO2S2 Tereahedra in the oxysulfide BaZnOS: a new coordination environment for Zinc in a condensed solid. al., S.Broadley et. Oxford : Inorganic Chemistry, 2005, Vol. 44. [3] Face-shared octahedral dimer In2O7S2 in the noncentrosymmetric Barium Indium Silicate Oxysulfide Ba2In2Si3O10S. Guo, W.H et al. s.l. : european journal of inorganic chemistry, 2016. [4] Oychalchogenide BaGeOSe2 highly distorted mixed-anion building units leading to a large Second-Harmonig generation response. Liu, K.W et al. s.l. : Chemistry of materials, 2015, Vol. 27.

Resume : Recently, water splitting using solar radiation as energy source to produce hydrogen fuel has attracted much attention. Overall water splitting consists of two reactions, the hydrogen (HER) and oxygen evolution reaction (OER). It is known that the latter reaction requires high overpotentials and the discovery and design of catalyst materials that overcome these high overpotentials is thus required. Oxides with the perovskite structure were reported to have good catalytic properties. However, their wide band gap limits their activity to the UV part of the solar spectrum. Substitution of oxygen with the less electronegative nitrogen narrows the band gap making oxynitrides suitable for photocatalysis. Layered perovskites were shown to have better photocatalytical activity than the non-layered ones. However, there are no studies on the OER activity of layered oxynitrides with the perovskite structure. In the present work, we investigate the electronic properties of the oxynitride Sr2TaO3N and its surfaces by density functional theory (DFT). Moreover, we investigate the OER activity on these surfaces by calculating the OER free energy changes and the overpotentials required on each surface to predict the most active surface and reaction site. We find that the (001) TaON-terminated surface is more relevant for photocatalysis due to its electronic features that may lead to suppression of electron-hole recombination and its low OER overpotentials.

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 includes 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 : Perovskite nanomaterials composed of LaMO3 (M = Fe, Co) are of current interest for environmental catalysis applications, e.g., oxidation of CO and CH4, and for catalytic energy conversion reactions such as water splitting. The synthesis of such compounds is commonly done in time and energy consuming batch processes. Alternatively, spray-flame synthesis (SFS) allows the formation of functional perovskite nanoparticles in a single step. Cost-efficient production requires the utilization of cheap and abundant precursors such as metal nitrates. However, the use of metal nitrates in SFS is often associated with the formation of particles non-homogeneous in size. Furthermore, the different melting/decomposition mechanisms and their different solubility in solvents such as ethanol cause the formation of undesired phases, e.g., La2CoO4, La2O3 and Co3O4, which are often obtained in parallel to the main perovskite phase. In order to improve the perovskite homogeneity in size and composition, mixtures containing the metal nitrate precursors and two different solvents, ethanol and 2-ethylhexanoic acid (2-EHA), were employed in this study. The incorporation of 2-EHA has been previously investigated and a positive effect toward narrow particle-size distributions has been observed. It is suggested that the addition of 2-EHA leads to the formation of micro-explosions in the droplets through superheating of ethanol and the formation of volatile metal carboxylates, which is investigated in this study. LaCoO3 and LaFeO3 nanoparticles were synthesized from solutions of the respective nitrates in ethanol/2-EHA. To understand the effect of 2-EHA on the product properties, temperature-dependent liquid-phase ATR-FTIR studies were performed. It was found that an esterification of 2-EHA with ethanol occurred forming ethyl-2-ethylhexanoate (verified by GC/MS). We assume that the metal nitrates act as catalysts as reported for similar reactions. The nanoparticle products were characterized using XRD, XPS, TEM, SAXS, and Mößbauer spectroscopy. The measurements confirm that the incorporation of 2-EHA in the solution was effective for obtaining homogeneous, single-phase, and high-surface-area products (LaCoO3: dp = 11 nm, SSA > 90 m2/g, LaFeO3: dp = 15 nm, SSA > 88 m2/g). The LaFeO3 and LaCoO3 perovskites were evaluated for the catalytic oxidation of carbon monoxide, reaching temperatures lower than 206°C for the 50% CO conversion.

Resume : Calcium tantalum oxynitride (Ca2Ta3O9N) nanosheet was prepared by exfoliating a layered perovskite oxynitride, Na2Ca2Ta3O9N, via proton exchange and two-step intercalation of ethylamine (EA) and tetrabutylammonium (TBA) ions. Intercalation of EA is essential for preparing nanosheets since TBA+ ions (the exfoliation reagent) are not intercalated into the protonated form without EA intercalation. Monolayer nanosheets could be prepared by the above processes, although some bilayer or trilayer nanosheets were also produced. The Ca2Ta3O9N nanosheets exhibited photocatalytic activity for H2 evolution from water under visible light irradiation in the presence of sacrificial agent. In contrast, NaCa2Ta3O9N exhibited lower photocatalytic activity compared with the nanosheet. The improved photocatalytic activity originates from their large surface area.

Resume : Photon upconversion featuring higher photon output than pump wavelength, has been well developed in lanthanide activator (e.g. Er3+, Ho3+ and Tm3+) over the past decade. However, the lack of transition-metal activated emission has restrictions on applications in some aspect. Herein, we report a strategy to realize manganese (II) upconversion in a CaZnOS semiconductor through co-doping of Er3+. Powder samples were obtained by simply mixing raw materials and calcination under high temperature. Phase purity was checked by powder X-ray diffraction. Photoluminescence emission (PL)/excitation (PLE), upconversion luminescence spectra and upconversion lifetime have been systematically investigated to reveal the underlying mechanism Mn2+ upconverison. By finely adjusting doping concentration of both Mn2+ and Er3+, we finally obtain comparable broad upconverison emission with maximum at 613 nm, arising from Mn2+, 4T1?6A1 optical transition. The Er3+ to Mn2+ energy transfer has been confirmed by the decreased lifetime in the emission of Er3+ at 562 nm. In addition, we are committed to enhance Mn2+ emission by improving energy transfer efficiency from Er3+ to Mn2+ and trying to tune the upconversion emission wavelength by manipulating host lattice. Despite above, the Er3+ and Mn2+ co-doping approach provides a good reference for designing and fabricating novel upconversion luminescent materials.

Resume : Rare-earth metal oxyhydrides, including yttrium oxyhydride (YOxHy), are promising mixed anion materials in view of their photochromic properties and hydride ion mobility. YOxHy thin-films are synthesized by reactive magnetron sputtering where the anion ratio is tuned by the deposition conditions. The present work focuses on elucidating the nature of hydrogen in YOxHy by muon spin rotation (μSR), employing the muon as a hydrogen-mimicking probe under zero field (ZF) and transverse magnetic field (TF) to explain structural and electronic properties respectively. The ZF data reveals the presence of μ+–H- or negative muonium (Mu-) –H- pairs via their entangled two-spin interaction. All extracted μ+-H- distances were substantially larger than the H2 molecular distance yet significantly smaller than the H?H distances in the crystal lattices of both YH2 and YOxHy. YH2 shows the presence of one type of μ+-H- pair, while the YOxHy samples indicate a spread in μ+-H- distances, possibly reflecting partial occupation of H- at octahedral sites and not only tetrahedral sites. The TF analysis shows that neutral muonium (Mu0) was formed in the semiconducting YOxHy films but not in the metallic YH2. In-situ UV illumination of the photochromic YOxHy films reduces the formation of Mu0, plausibly related to the generation of charge carriers upon photodarkening. These carriers can interact with Mu0 to form Mu-, or Mu0 itself can be excited by the light exposure and release its electron forming μ+.

Resume : Rare Earth (RE) metal oxy-hydrides are promising multi anion materials which show photochromic properties under ambient conditions. Their transmittance decreases reversibly by exposure to sunlight and this effect may extend from the UV up to the mid-IR [1]. Therefore these materials are not only suitable for visible light-modulation but they can also act as a barrier to solar thermal radiation. In our latest work we show that it is possible to synthesize two different kinds of RE-based line compounds by reactive magnetron sputtering: the hydroxides and oxyhydrides [2]. Only the oxyhydrides are photochromic and this study attempts - in two steps - to shed insight into the origin of such difference. First, we complement the picture with structural analysis (XRD & EXAFS). In doing so, we also establish that the oxygen atoms occupy tetrahedral sites in the cubic lattice (Ia-3) of the oxyhydrides; supporting thus the anion-disordered model proposed in [2]. Second, the compositional and structural information is used to compute by DFT the band structures of the two types of materials. The comparison of the P-DOS suggests that hydrogen plays a distinctly different role in defining the electronic and optical properties of the two line compounds. References: [1] F. Nafezarefi et al. Appl. Phys. Lett. 111 (2017) 103903 [2] S. Cornelius et al., J. Phys. Chem. Lett. (2019) submitted

Resume : Mixed anion materials are highly known to present tunable properties thanks to anion substitution. 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. Moreover, as a gas/solid synthesis technique, it is known to be environment-friendly method, widely used in industry. In the present study, we focus on deposition of tantalum oxynitrures (by sputtering a tantalum target in Ar/O2/N2 atmosphere) and bismuth oxyfluorides (from bismuth target in Ar/O2/CF4 atmosphere) as photocatalysts. RBS shown films with composition varying from tantalum/bismuth oxide to tantalum nitride or bismuth fluoride are obtained. Nature of these deposits was deeply investigated by XPS, FTIR, and XRD, associated to Pair Distribution Function technique. Films can be considered as randomly mixed compounds at very short scale (< few nm). Optical properties, followed by UV-visible spectroscopy and spectroscopic ellipsometry, are explained by the contribution of these different compounds leading to varisou metallic, semiconductor or insulator global behavior of the layer. Moreover, fine bandgap engineering is achieved for tantalum oxynitrides with values ranging from 1.7 to 2.7 eV with N to O substitution and for oxyfluoride (4-4.8 eV). These light absorption properties were then link to difference in photocatalytic activities.

Resume : Anion-lattice engineering for Cr4+-rich perovskite materials via topochemical routes has an unexplored area because (i) the tetravalent chromium cation prefers a tetrahedral coordination to an octahedral coordination and (ii) the ionic radius is too small in size to be incorporated into perovskite structures. However, utilizing high pressure synthesis can stabilize high-valent chromium perovskite oxides, which will be promising precursors for low-temperature reactions. We report the fluorination of SrCrO3 by PVDF for the first time, in which a superstructured oxide SrCrO2.8 was formed as an intermediate phase. SrCrO2.8 had not been obtained as a single phase, but we could successfully synthesize this phase as a single phase for the first time using carbothermal reduction technique.

Resume : The perovskite RMnO3 (R=rare-earth) exhibits a rich variety of physical properties depending on the type of rare-earth. When R site is doped alkaline earth mental elements, the compound becomes ferromagnetic through the double-exchange interaction. In this present, we have studied the crystal structure and magnetic properties for co-doping Y0.3Lu0.7MnO3 single crystalline by performing X-ray diffraction and magnetization measurements, respectively. The sample of Y0.3Lu0.7MnO3 single crystal with pure phase was grown by the floating-zone method. Experiments shows the characteristics of re-entrant spin glass behavior at low temperatures in the c axis, but no such behavior in the a axis for Y0.3Lu0.7MnO3 single crystal. The refinement results of X-ray diffraction pattern reveal that pure single-phase sample exhibits hexagonal structure with P63cm space group. Upon cooling, it undergoes multiple magnetic phase transitions, i.e., antiferromagnetic, weak ferromagnetic, and spin glass transitions along its c axis. And it only undergoes antiferromagnetic transition along the a axis over the whole measured temperature range, indicating that 70% Lu doping leads to the change of magnetic anisotropy. The magnetic properties show that re-entrant spin glass behaviour in Y0.3Lu0.7MnO3 single crystal mainly results from the magnetic frustration and the disorder coming from Lu dopant. In addition, the magnetic frustration is correlated with the competition between the antiferromagnetic and weak ferromagnetic interactions. The present study would be helpful for people to understand the physical behavior in co-doped R1-xAxMnO3 manganite compounds.

Resume : Sillen-Aurivillius type structure consists of [An-1BnO3n-1] layer (n = the number of perovskite blocks) sandwiched by double [Bi2O2] layers and single halide [X] layer along the c axis. Several interesting chemical and physical properties were found in this series of compounds. For example, n = 1 Bi4NbO8X (X = Cl, Br) is a novel photocatalyst for water splitting[1], as well as a potential Pb-free ferroelectric material[2]. Furthermore, Sillen?Aurivillius type structure is designable by changing the block of layers. How these properties differ by changing the layer, such as inserting one perovskite block to form Bi3Pb2Nb2O11Cl (n = 2), is also worthwhile studying. In order to obtain further insight into these properties, such as carrier dynamics for photocatalyst, the measurements using single crystals are desirable. However, details about single crystal growth of Sillen?Aurivillius compounds have not been reported yet. In this work, single crystals of Bi4NbO8X were successfully obtained after examining and optimizing synthetic conditions such as heating temperature, keeping time and cooling rate. The key to growing the single crystal of multi-anion compounds was finding a proper condition that can suppress the volatilization of different anionic species. By using this knowledge, the single crystal of Bi3Pb2Nb2O11Cl was successfully obtained as well. References: [1] Fujito, H., et al. J. Am. Chem. Soc. 2016, 138, 2082-2085. [2] Kusainova, A. M., et al. Chem. Mater. 2001, 13, 4731-4737.

Resume : LaMnO3 perovskite is currently being investigated as a potential and inexpensive alternative to noble metals (e.g. Pd or Pt) for catalytic reactions. A specific focus is on decontamination and purification reactions such as the preferential oxidation (PROX) of CO in excess hydrogen. In order to synthesize suitable, high surface area LaMnO3 nanomaterials, the spray-flame synthesis (SFS) technique was used as it provides a continuous, single step and cost-efficient production way. Concerning the formation of a functional and active catalyst, the main challenges of this technique include avoiding multimodal and broad particle size distributions, the formation of secondary non-active phases such as La2O3, and low reducibility. Metal nitrates as cost-effective precursors were dissolved in solutions containing ethanol or mixtures of ethanol and 2-ethylhexanoic acid (2-EHA), whereas the latter combination is known to support the formation of extremely fine-grained nanomaterials. A specific interest was in the thermal and chemical stability of the as-prepared solutions. Therefore, liquid phase temperature-dependant ATR-FTIR and UV-VIS studies were performed. While the ethanol solutions didn?t show any changes in chemical composition, esterification between ethanol and 2-EHA was observed most likely catalyzed by manganese. Moreover, the oxidation of Mn2+ to Mn3+ and Mn4+ was found above 40°C. However, these solutions showed an excellent stability and enabled the formation of small particles with a unimodal and narrow size distribution (dp = 7.3 nm). Traces of an oxygen-rich LaMnO3 phase were identified on the particles’ surface containing a Mn4+/Mn3+ ratio of 0.5 (XPS). The samples were evaluated for CO-PROX, obtaining at 220°C a conversion of CO of 85% while keeping the conversion of hydrogen below 10%.

Resume : Half-metallic ferromagnets (HMFs) have the potential to apply in many fields related to electronic transport and spintronics and are worth further investigation. HMFs exhibit a semiconductor behavior in one spin band at the Fermi level. Among some kinds of HMFs, Co-based Heusler alloys are of particular interest due to comparatively high Curie temperatures. Mechanical alloying (MA) has been applied to produce nanocrystalline Co2MnSi Heusler alloys. A two-phase mixture of amorphous phase and remaining Mn were obtained after 5 hours of MA without any evidence for the formation of Co2MnSi alloys. The saturation magnetization of MA powders decreased with MA time due to the magnetic dilution by alloying with nonmagnetic Mn and Si elements to 48 emu/g after 5 hours of MA. On the other hand, a Co2MnSi single phase was obtained by MA after 3 hours and subsequently heat treated up to 650°C. X-ray diffraction result showed that the average grain size of Co2MnSi Heusler alloys prepared by MA for 5 hours and heat treatment to be in the range of 85 nm. The saturation magnetization of Co2MnSi Heusler alloys prepared by MA and heat treatment reached a maximum value of 112 emu/g for 5 hours MA sample. It was also observed that the coercivity of 5 hours MA sample annealed at 650°C was fairly low value of 27 Oe.