Electron Microscopy for Materials Research (EMAT), University of Antwerp , Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
Skoltech Center for Electrochemical Energy Storage, Skolkovo Institute of Science and Technology , 143026 Moscow, Russia.
J Am Chem Soc. 2016 Mar 9;138(9):3211-7. doi: 10.1021/jacs.6b00088. Epub 2016 Feb 23.
We present how the introduction of anion vacancies in oxyhydrides enables a route to access new oxynitrides, by conducting ammonolysis of perovskite oxyhydride EuTiO3-xHx (x ∼ 0.18). At 400 °C, similar to our studies on BaTiO3-xHx, hydride lability enables a low temperature direct ammonolysis of EuTi(3.82+)O2.82H0.18, leading to the N(3-)/H(-)-exchanged product EuTi(4+)O2.82N0.12□0.06. When the ammonolysis temperature was increased up to 800 °C, we observed a further nitridation involving N(3-)/O(2-) exchange, yielding a fully oxidized Eu(3+)Ti(4+)O2N with the GdFeO3-type distortion (Pnma) as a metastable phase, instead of pyrochlore structure. Interestingly, the same reactions using the oxide EuTiO3 proceeded through a 1:1 exchange of N(3-) with O(2-) only above 600 °C and resulted in incomplete nitridation to EuTiO2.25N0.75, indicating that anion vacancies created during the initial nitridation process of EuTiO2.82H0.18 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.
我们展示了通过对钙钛矿氧氢化物 EuTiO3-xHx（x∼0.18）进行氨解反应，如何引入阴离子空位来实现制备新型氧氮化物的途径。在 400°C 下，与我们对 BaTiO3-xHx 的研究类似，氢化物的不稳定性使得低温下可以直接对 EuTi(3.82+)O2.82H0.18 进行氨解反应，从而得到 N(3-)/H(-)交换产物 EuTi(4+)O2.82N0.12□0.06。当氨解温度升高到 800°C 时，我们观察到进一步的氮化反应涉及 N(3-)/O(2-)交换，生成具有 GdFeO3 型畸变（Pnma）的完全氧化的 Eu(3+)Ti(4+)O2N 作为亚稳相，而不是焦绿石结构。有趣的是，使用氧化物 EuTiO3 的相同反应仅在 600°C 以上通过 N(3-)与 O(2-)的 1:1 交换进行，并且导致不完全氮化至 EuTiO2.25N0.75，表明在 EuTiO2.82H0.18 的初始氮化过程中形成的阴离子空位在促进高温下阴离子（N(3-)/O(2-)）交换中起着关键作用。因此，通过使用（氢化物诱导的）阴离子缺陷前体，我们应该能够扩展钙钛矿氧氮化物的可访问阴离子组成。
