Formation and Structural Characterization of 1:1 Ordered Perovskites in the Ba(Zn1/3Ta2/3)O3–BaZrO3 System

The phase stabilities in the(1−x)Ba(Zn_1/3Ta_2/3)O₃ (BZT)-xBaZrO₃(BZ)system have been investigated using samples prepared by the mixed oxide method. The substitution of Zr⁴⁺destabilizes the 1:2 cation ordering in BZT and pro-motes the formation of a cubic, 1:1 ordered structure with a doubled perovskite repeat. The homogeneity range of the 1:1 phase extends from x = 0.04 to approximately x = 0.25; substitutions beyond this range stabilize a disordered perovskite. The limits of stability of the 1:1 ordering coin-cide with compositions previously found to exhibit anoma-lies in their dielectric loss. The range of homogeneity is consistent with a "random layer" model for the 1:1 ordered "Ba{β';_1/2β^1/2}O₃" structure. In this model the B× positions are assumed to be occupied exclusively by Ta⁵⁺, and the b× sites by a random distribution of Zn₂₊, Zr₄₊, and the remaining Ta 5+ cations. The validity of the model, where the ordered solid solutions can be represented by Ba{[Zn_{2− y /3}Ta_{(1−2 y )/3}Zr y ]_1/2[Ta]_1/2}O₃(y =2x)was con-firmed by Rietveld refinements conducted using data col-lected with a synchrotron X-ray source.