Phase Equilibria and Dielectric Properties in Perovskite-like (1 − x)LaCa_0.5Zr_0.5O₃–xATiO₃ (A = Ca, Sr) Ceramics

Phase equilibria and dielectric properties were analyzed for selected compositions in both LaCa_0.5Zr_0.5O₃–CaTiO₃ (LCZ-CT) and LaCa_0.5Zr_0.5O₃–SrTiO₃ (LCZ–ST) systems using x-ray powder diffraction and transmission electron microscopy. The end-member LaCa_0.5Zr_0.5O₃ does not occur as a single phase but rather as a mixture of a perovskite-type phase with approximate composition La_0.94Ca_0.53Zr_0.53O₃ 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.