Can we predict the formability of perovskite oxynitrides from tolerance and octahedral factors?

Abstract

Perovskite oxynitrides AB(O,N)₃ represent an emerging class of materials suitable for applications in the fields of clean energy and environmental protection. Nitrogen substitution for oxygen allows for a significant enrichment of possible perovskite structures for combinations of cations that are not achievable in perovskite oxides. A model that utilizes the tolerance and octahedral factors is developed for assessing the formability of the perovskite structure in oxynitrides and for predicting new perovskite oxynitrides that have not been synthesized so far. Our model considers the alteration of the interatomic distances and cationic radii in oxynitrides when compared to those in oxides and nitrides. In the first step we identify the stability field of the perovskite structure in oxynitrides from the crystal structure data for perovskite oxynitrides synthesized so far. In the next step we address the formability of the perovskite structure for compositions not studied yet. For instance, we predict that among potentially piezoelectric oxynitrides, YSiO₂N and YGeO₂N are not stable in the perovskite-type structure; YZrO₂N and YSnO₂N are in turn formable, whereas for possible candidate of photocatalytic oxynitrides according to DFT calculations MgTaO₂N is not formable in perovskite structure; YTiO₂N, CdTaO₂N and CdNbO₂N appear to be feasible. Moreover, we predict the formability of perovskite structures for Zn²⁺, Cd²⁺, Y³⁺, Hf⁴⁺, Fe⁴⁺and Sn⁴⁺, as well as Pr³⁺, Nd³⁺, and Sm³⁺ oxynitrides. As none of these compounds has been yet synthesized, our model can be applied for designing and guiding the synthesis of novel perovskite structures in oxynitrides.