RARE-EARTH PLATINUM-GROUP MIXED-METAL OXIDE SYSTEMS

The phase development in rare earth-platinum group oxide (RE-PG-O) sys tems has been investigated by reacting selected compositions in sealed evacuated silica vials and characterizing the products using X-ray di ffraction. PG(II), PG(III), PG(IV) and PG(V) species, where PG = Ru, I r, Rh, Pd and Pt, have been stabilized in these systems in various str ucture types. For PG(II) these include the Nd2CuO4-type structure and other fluorite-related derivatives; for PG(III), orthorhombically dist orted perovskite; for PG(IV), the pyrochlore structure; for PG(V), alp ha- and gamma-A3BO7 types, which are also ordered fluorite derivative structures. The rare earth has a secondary effect on RE-PG-O phase dev elopment, with the half-filled 4f shell of the Gd representing a trans ition point for structural stability in the RE series. Systems contain ing 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 gamma-RE3PGO7, have been synthesize d.