Deciphering Anion Order in Oxysulfide Perovskites: Origins and Implications

Perovskite compounds—with a generic formula of ABX3— represent a versatile class of materials exhibiting tremendous synthetic flexibility and technological applications. Going beyond “single” perovskites, two or more species can occupy each sublattice. While origins and design rules of cation ordering in perovskites are well known, anion ordering in heteroanionic perovskites remains a largely uncharted territory. This talk will share insights from a first principles analysis of anion-ordered AB(O0.5S0.5)3 oxysulfide chemistries, studied in all possible anion configurations, with A=Ca,Sr,Ba and B=Ti,Zr,Hf. We find that the stable local ordering is always an all-cis arrangement (i.e., a fac-type ordering) in each BO3S3 octahedron, stabilized by a combination of electronic, strain and electrostatic interactions. We further study the relative stability of this ordering as a function of A and B site chemistries and probe its effect on the electronic structure. Most remarkably, we show that the ground state anion ordering breaks inversion symmetry to create a family of polar oxysulfides with polarization >30 µC/cm2, exhibiting a significant promise for electronic applications.