Anion diffusion in mixed-anionic perovskite systems
September 4-8, 2016
Mixed anion compounds, where a transition metal is coordinated by more than one anion species, are a new and emerging class of materials that can show novel or improved functionalities. However, preparation of mixed anion compounds such as oxyhydrides and oxynitrides has been a big challenge; A conventional high-temperature reaction often fails due to the significant difference in anion characters (O2–, H–, S2–, F–, N3–,...). Low-temperature topochemical reactions are an effective strategy to access mixed anion compounds. In my presentation, I would like to present our recent works on topochemical reactions for new mixed anion compounds. For example, oxyhydride perovskite BaTi(O,H)3 obtained by the CaH2 reduction of BaTiO3 shows remarkable hydride diffusion at moderate temperatures (~400 °C) . Interestingly, the labile nature of hydride (H–) ions in this oxyhydride allows a N3–/H– exchange to occur by a low temperature (< 500 °C) ammonolysis (NH3) reaction, in marked contrast with currently available oxynitride synthetic routes . Surprisingly, the same reaction can proceed with the otherwise inert N2 gas, yielding BaTi(O,N)3 (see Figure 1) . When one use EuTi(O,H)3, the hydride lability enables the creation of anion vacancies, which in turn facilitate the nitridation of an oxide, yielding Eu3+Ti4+O2N, which is not accessible from EuTiO3 (see Figure 2) . This means that, by paying attention to the role of anion vacancies in solids, we should be able to expand the accessible range of oxynitrides, leading to the discovery of new materials.
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Hiroshi Kageyama, "Anion diffusion in mixed-anionic perovskite systems" in "Nonstoichiometric Compounds VI", ECI Symposium Series, (2016). http://dc.engconfintl.org/nonstoichiometric_vi/24