Crystal Chemistry of New Layered Oxyhalide Perovskites with Anion Order

Abstract

We have successfully synthesized new members of layered perovskite oxyhalides with the Ruddlesden-Popper type structure by a high pressure, high temperature method. We found that the halide ions exclusively occupied apical anion sites leading to modifications of coordination environment around the metal centers. Such site preferences of mixed anions provide good opportunities for extending structure and properties of transition metal oxides or halides. Here we present square planar coordination stabilized in Jahn-Teller inactive oxychlorides Sr₂MO₂Cl₂（M＝Mn, Ni, Zn）, a spin ordered/disordered state triggered by anion ordered patterns in Sr₂NiO₃X（X＝F, Cl）, and a novel pressure-induced spin state transition involving a polyhedral transformation in Sr₂CoO₃F.