ANIM 2: Advances and Enhanced Functionalities of Anion-controlled New Inorganic Materials

Resume : Combining electrical and magnetic properties is highly desired in the field of multiferroics. For example, attempts were made to add magnetic dn cations to ferroelectric Aurivillius phases, which unfortunately gives spin glasses. We have investigated an alternative parent compound hematophanite, a combination of perovskite slabs and halide layers, and have succesfully made a homologous series An+1BnO3n-1Cl based on it. We characterized the compounds using NPD and atomic resolution TEM. All compounds are G-type antiferromagnetic, and their Neel temperature is independent of the thickness of the perovskite blocks. An interesting feature is their layered order at the B cation positions. This is extremely rare in perovskites when not coupled with simultaneous order of the oxygen atoms and vacancies. There is also Ti in square pyramidal coordination, which exists in only very few compounds. Following our observation of PbBiO2 defects in higher members of the series, we also designed and succesfully synthesized single phases of a second new homologous series [PbBiO2]An+1BnO3n-1Cl2 that combines An+1BnO3n-1 perovskite and -PbO type [A2O2] blocks and halide layers. While the hematophanite has one magnetic slab per unit cell, the second series has two, in a body centered arrangement that cancels exchange interactions. The two new homologous series leave a lot of room for experimenting with further adaptations. A.A. is grateful to RSF for financial support (grant 14-13-00680)

Resume : This contribution presents the synthesis of perovskite compounds as oxide and oxynitride thin films. The (Sr0.99La0.01)2(Ta0.99Ti0.01)2O7 oxide composition has been chosen to achieve a ferroelectric Curie temperature close to 300 K. Its nitridation results in the (Sr0.99La0.01)(Ta0.99Ti0.01)O2N oxynitride composition. Depositions are made by RF magnetron sputtering, with both O2 and N2 in the reactive part of the plasma. The deposition discharge content is studied by optical emission spectroscopy and is correlated with both the deposition rate and the films structure. Dielectric properties are also measured to evaluate the potential for integrating these materials into agile and/or miniaturized antennas. Without dinitrogen in the discharge, oxide thin films are epitaxially grown on single-crystalline MgO (001) substrate, with a band-gap value close to 4.5 eV in good accordance with literature values reported for Sr2Ta2O7. Introducing dinitrogen into the plasma leads to a decrease in the films crystalline quality and the oxynitride contribution becomes predominant. The film deposited under a dinitrogen/argon mixture (i.e. without dioxygen) exhibits a pure oxynitride structure with a strong (00l) preferred orientation and a band-gap of 2.45 eV, close to the SrTaO2N bulk value. Further results on plasma, structure and dielectric characterizations will be discussed in the final contribution.

Resume : Electron diffraction tomography (EDT) based on taking electron diffraction patterns of crystals out of zone axis is used for the ab initio structure determination of a single nm-sized crystals, potentially allowing detection of the light elements, such as Li. Due to low electron dose this technique is appropriate for the study of Li- or Na-based battery materials which are inaccessible with other electron microscopy techniques. Furthermore, only a small amount of sample is needed for such experiment, which is an important advantage for studying charged cathodes. The structure solution of LiFePO4 was performed from EDT data using PETS software (Palatinus, 2011) demonstrating a quality comparable to that for powder X-ray diffraction. By the use of difference Fourier maps the position of the Li atoms was determined. The refinement revealed the atomic coordinates were in a good agreement with the literature data and the values of the bond valence sums correspond to nominal cation and anion valences. Ex-situ experiments were performed on pristine and charged (4.3V) LiFe0.5Mn0.5PO4. The presence of Li atoms in the latter was not revealed, which is consistent with the full delithiation process. A clear difference in the unit cell parameters between the pristine and charged samples has been detected. These examples demonstrate that EDT is a reliable method of structure determination for cathode materials from submicron-sized crystallites.

Resume : Over the last decade, p-type semiconductors (SC) have known a renewed interest. Indeed these materials may have potential applications for light-emitting diodes, transistors, solar cells, etc. Since the achievement of the first Dye Sensitized Solar Cells by Grätzel [1] in 1991 a new generation of solar cells has been developed [2] where the n-type SC is replaced by a p-type one. This leads to the photo-injection of holes instead of electrons in the circuit. To date nickel oxide (NiO) is the reference p-type semiconductor. However yields are still far from those of DSSC-n and many studies aim to replace NiO by other systems such as CuAlO2, CuGaO2, CuCrO2 or NiCo2O4 nanoparticles. Following our recent synthesis of N doped ZnO with stabilization of p-type charge carriers [3], we focus now on the preparation of N doped NiO nanoparticles to improve the p-type conductivity of NiO. We will study here the chemical reactivity of a nickel oxohydroxo precursor under air and ammonia that conducts to nanostructured Ni-poor NiO. References: 1. B. O'Regan, M. Grätzel, Nature 353, 737-740 (1991). 2. F. Odobel, L. Le Pleux, Y. Pellegrin, E. Blart, Acc. Chem. Res., 43, 1063−1071, (2010). 3. B. Chavillon, L. Cario, A. Renaud, F. Tessier, F. Cheviré, M. Boujtita, Y. Pellegrin, E. Blart, A. Smeigh, L. Hammarström, F. Odobel, S. Jobic, J. Am. Chem. Soc. 134, 464-470 (2012).

Resume : Zinc oxide is a material of great interest exhibiting pigmental, photocatalytic, piezoelectric, antibacterial, or varistor properties that have already been developed in many different fields of industry. Still novel applications emerge in various domains but they often require the preliminary stabilization of a p-type ZnO counterpart to the natural n-type ZnO to be stimulated. In optoelectronics for instance, the high optical transparency of ZnO thin films coupled with their high electrical conductivity and their strong room temperature luminescence could indeed open up the door to revolutionary technologies as transparent electrodes in solar cells and flat panel displays, light emitting diodes, lasers, etc. We have previously reported the stabilization of p-type nitrogen doped Zn1 xO nanoparticles (ZnO:N) obtained through the decomposition of zinc peroxide (ZnO2) at low temperature under ammonia flow [1]. Our objective is now to extend these results to the realization of p-type ZnO thin films by colloidal route in order to achieve n-ZnO/p-ZnO:N homojonctions which would led to various applications in optoelectronics. The aim of the present work is to prepare nitrogen doped Zn1-xO thin film by thermal decomposition of ZnO2 films obtained by chemical conversion of ZnO colloidal thin films. [1] B. Chavillon, L. Cario, A. Renaud, F. Tessier, F. Cheviré, M. Boujtita, Y. Pellegrin, E. Blart, A. Smeigh, L. Hammarström, F. Odobel, S. Jobic, J. Amer. Chem. Soc. 134, 464-470 (2012)

Resume : Phosphates, especially aluminophosphate oxynitrides (AlPOxNy), are known to present attractive properties for basic catalysis. The nitrogen (N3-) / oxygen (O2-) substitution has been reported within X-rays amorphous metallophosphates (Al-P-O, Ga-P-O, Al-Ga-P-O, Zr-P-O, In-P-O, Ti-P-O) by thermal reaction under ammonia flow. The resulting metallophosphate oxynitride powders maintain the high specific surface area of the precursor making them interesting catalysts, and moreover, the incorporation of nitrogen in the anionic network is an effective way to modify the surface acid-base properties. In collaboration with the Institut Français du Pétrole-Energies Nouvelles (IFPEN), we study the interest of such phases, as heterogeneous catalysts, in the transesterification reaction of vegetable oils.