Phase equilibria and dielectric properties in perovskite-like (1-x)LaCa0.5Zr0.5O3-xATiO3 (A = Ca, Sr) ceramics

Phase equilibria and dielectric properties were analyzed for selected compositions in both LaCa(0.5)Zr(0.5)O(3)-CaTiO(3) (LCZ-CT) and LaCa(0.5)Zr(0.5)O(3)-SrTiO(3) (LCZ-ST) systems using x-ray powder diffraction and transmission electron microscopy. The end-member LaCa(0.5)Zr(0.5)O(3) does not occur as a single phase but rather as a mixture of a perovskite-type phase with approximate composition La(0.94)Ca(0.53)Zr(0.53)O(3) plus a minor amount of La(2)O(3). This perovskite phase exhibited a combination of 1:1 ordering of Ca and Zr on the B-sites and octahedral tilting. In the (I - x)LCZ-xCT system, the compositions x = 1/3 and x = 1/2 yielded single phases with perovskite-like structures featuring similar 1:1 B-site ordering superimposed onto octahedral tilting. The x = 1/2 composition in the LCZ-ST system resides in a two-phase field and contains a major perovskite phase and La(2)O(3); the B-cations in the perovskite phase remain disordered at all temperatures. The approximate boundaries of perovskite-like phase fields in the La(2)O(3)-ATiO(3)-CaZrO(3) (A = Ca, Sr) systems were outlined, as well as a schematic diagram for perovskite B-cation ordering transitions in the LCZ-CT system. The dielectric properties of the compositions investigated were measured at microwave frequencies and were correlated with the observed structural behavior.