Rare earth—platinum group mixed metal oxide systems

The phase development in rare earth—platinum group oxide (RE---PG---O) systems has been investigated by reacting selected compositions in sealed evacuated silica vials and characterizing the products using X-ray diffraction. PG(II), PG(III), PG(IV) and PG(V) species, where PG Ru, Ir, Rh, Pd and Pt, have been stabilized in these systems in various structure types. For PG(II) these include the Nd₂CuO₄-type structure and other fluorite-related derivatives; for PG(III), orthorhombically distorted perovskite; for PG(IV), the pyrochlore structure; for PG(V), - and γ-A₃BO₇ types, which are also ordered fluorite derivative structures. The rare earth has a secondary effect on RE---PG---O phase development, with the half-filled 4f shell of the Gd representing a transition point for structural stability in the RE series. Systems containing La and Ce exhibit anomalous behaviour with respect to other RE---PG---O systems. In the course of the present study 28 new phases including a new polymorphic type, designated γ-RE₃PGO₇, have been synthesized.