FORMATION AND STRUCTURAL CHARACTERIZATION OF 1 1 ORDERED PEROVSKITES IN THE BA(ZN1/3TA2/3)O-3-BAZRO3 SYSTEM/

The phase stabilities in the (1-x)Ba(Zn1/3Ta2/3)O-3 (BZT)-xBaZrO(3) (B Z) system have been investigated using samples prepared by the mixed-o xide method. The substitution of Zr4+ destabilizes the 1:2 cation orde ring in BZT and promotes the formation of a cubic, 1:1 ordered structu re with a doubled perovskite repeat. The homogeneity range of the 1:1 phase extends from x = 0.04 to approximately x = 0.25; substitutions b eyond this range stabilize a disordered perovskite. The limits of stab ility of the 1:1 ordering coincide with compositions previously found to exhibit anomalies in their dielectric loss. The range of homogeneit y is consistent with a ''random layer'' model for the 1:1 ordered ''Ba {beta(1/2)'beta(1/2)''}O-3'' structure. In this model the beta '' posi tions are assumed to be occupied exclusively by Ta5+, and the beta' si tes by a random distribution of Zn2+, Zr4+, and the remaining Ta5+ cat ions. The validity of the model, where the ordered solid solutions can be represented by Ba{[Zn(2-y/3)Ta(1-2y/3)Zr-y](1/2)[Ta](1/2)}O-3 (y = 2x) was confirmed by Rietveld refinements conducted using data collec ted with a synchrotron X-ray source.