Topochemical Nitridation with Anion Vacancy-Assisted N~(3-)/O~(2-) Exchange

摘要

We present how the introduction of anion vacancies in oxyhydrides enables a route to access new orynitrides, by conducting ammonolysis of perovskite oxyhydride EuTiO_(3-x)H_x (x ～ 0.18). At 400 ℃, similar to our studies on BaTiO_(3-x)H_x, hydride lability enables a low temperature direct ammonolysis of EuTi~(3.82+)O_(2.82)H_(0.18), leading to the N~(3-)/H~--exchanged product EuTi~(4+)O_(2.82)N_(0.12)□_(0.06). When the ammonolysis temperature was increased up to 800 ℃, we observed a further nitridation involving N~(3-)/O~(2-) exchange, yielding a fully oxidized Eu~(3+)Ti~(4+)O_2N with the GdFeO_3-type distortion (Pnma) as a metastable phase, instead of pyrochlore structure. Interestingly, the same reactions using the oxide EuTiO_3 proceeded through a 1:1 exchange of N~(3-) with O~(2-) only above 600 ℃ and resulted in incomplete nitridation to EuTiO_(2.25)N_(0.75), indicating that anion vacancies created during the initial nitridation process of EuTiO_(2.82)H_(0.18) play a crucial role in promoting anion (N~(3-)/O~(2-)) exchange at high temperatures. Hence, by using (hydride-induced) anion-deficient precursors, we should be able to expand the accessible anion composition of perovskite oxynitrides.