Cation Ordering Transformations in the Ba(Zn _1/3 Nb _2/3 )O ₃ ‐La(Zn _2/3 Nb _1/3 )O ₃ System

Single‐phase perovskites were formed in the (1− _x )Ba(Zn _1/3 Nb _2/3 )O ₃ ‐( _x )La(Zn _2/3 Nb _1/3 )O ₃ system for compositions with 0.0≤ x ≤0.6. Although the stability of the trigonal “1:2” ordered structure of the Ba(Zn _1/3 Nb _2/3 )O ₃ end member is very limited (0.0≤ x ≤0.05), low levels of lanthanum induce a transformation to a cubic, “1:1” ordered structure that has a broad range of homogeneity (0.05≤ x ≤0.6). Samples with x > 0.6 were comprised of La ₃ NbO ₇ , ZnO, and a perovskite with x = 0.6. The cubic 1:1 phases were fully ordered and no evidence was found for a compositionally segregated microstructure. These observations could not be reconciled in terms of a “space‐charge” model; rather, they supported a charge‐balanced, “random‐site” structure for the 1:1 cation‐ordered Ba(β _1/2 ′β _1/2 ″)O ₃ phases.