Influence of the processing way for La3+-doping on crystal structure, microstructure, and microwave dielectric properties of Ca0.7Ti0.7La0.3Al0.3O3 ceramics

Perovskite ceramics with a formula of Ca0.7Ti0.7La0.3Al0.3O3 (CTLA) were produced through a conventional solid-state reaction procedure following three different La3+-doping methods using powders of La2O3, or La2O3/Al2O3 powder mixture, or LaAlO3. La3+ doping favored grain growth and densification, affected the grain size distribution, and improved the dielectric properties of the produced sintered CTLA ceramics. The doping methods had a strong influence on these properties. More specifically, doping with La2O3 and La2O3/Al2O3 resulted in formation of solid solution, while a secondary phase formed in the CTLA ceramics doped with LaAlO3, which caused a coarsening of the microstructure and lowered the La3+ doping effects on the dielectric properties. The experimental results suggest that La3+ doping improves the dielectric properties of the sintered CTLA perovskite ceramics, which are further enhanced by doping with Al3+ ions in small amounts. However, further increase of Al3+ ions content jeopardizes them.