Phase Equilibria and Dielectric Properties in Perovskite-like (1 − x)LaCa0.5Zr0.5O3–xATiO3 (A = Ca, Sr) Ceramics

Abstract

Phase equilibria and dielectric properties were analyzed for selected compositions in both LaCa0.5Zr0.5O3–CaTiO3 (LCZ-CT) and LaCa0.5Zr0.5O3–SrTiO3 (LCZ–ST) systems using x-ray powder diffraction and transmission electron microscopy. The end-member LaCa0.5Zr0.5O3 does not occur as a single phase but rather as a mixture of a perovskite-type phase with approximate composition La0.94Ca0.53Zr0.53O3 plus a minor amount of La2O3. This perovskite phase exhibited a combination of 1:1 ordering of Ca and Zr on the B-sites and octahedral tilting. In the (1 – 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 La2O3; the B-cations in the perovskite phase remain disordered at all temperatures. The approximate boundaries of perovskite-like phase fields in the La2O3–ATiO3–CaZrO3 (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.