Studies of the 4d and 5d 6H perovskites Ba3BM2O9, B = Ti, Zn, Y; M = Ru, Os, and cubic BaB1/3Ru2/3O3 polymorphs stabilised under high pressure

Abstract

The synthesis, structures and magnetism of six mixed 3d–5d oxides Ba₃BM₂O₉ (B = Ti, Y, Zn; M = Ru, Os) are described. When prepared at ambient pressure the six oxides display a 6H type perovskite structure comprised of corner sharing BO₆ and face sharing M₂O₉ motifs. Synchrotron X-ray diffraction reveals a small monoclinic distortion in Ba₃ZnRu₂O₉; the remaining oxides exhibit a hexagonal structure. The magnetic properties are dominated by the M–M interactions across the shared face. Only in the mixed valent (M⁴⁺/M⁵⁺) Y oxides is evidence of long-range magnetic order found. Application of high pressure/high temperature synthetic methods for the Ru containing oxides changes the structure to the archetypical cubic Pmm perovskite structure, where the B and Ru cations are disordered on the corner sharing BO₆ octahedral sites. The magnetic properties of the cubic oxides are dominated by short range antiferromagnetic interactions, the chemical disorder inhibiting long range ordering.