Effect of La³⁺ substitution on microwave dielectric properties of (Pb_0.5Ca_0.5)(Fe_0.5Nb_0.5)O₃ ceramics

Microwave dielectric properties of the [(Pb_0.5Ca_0.5)_1−x La_2x/3](Fe_0.5Nb_0.5)O₃ and [(Pb_0.5Ca_0.5)_1−x La _x ](Fe_0.5Nb_0.5)O₃ ceramics were investigated as a function of La³⁺ content \( {\left( {0.0 \leqslant \times \leqslant 0.2} \right)} \). A single perovskite phase was detected in [(Pb_0.5Ca_0.5)_1−x La_2x/3](Fe_0.5Nb_0.5)O₃, while Pb₃Nb₄O₁₃ were detected as a secondary phase in [(Pb_0.5Ca_0.5)_1−x La _x ](Fe_0.5Nb_0.5)O₃ beyond x = 0.05 due to the excess of unbalanced charge. The amount of Pb₃Nb₄O₁₃ was proportional to the unbalanced charge. Qf value of [(Pb_0.5Ca_0.5)_1−x La_2x/3](Fe_0.5Nb_0.5)O₃ decreased remarkably with La³⁺ substitution due to the increase of oxygen vacancy. For [(Pb_0.5Ca_0.5)_1−x La _x ](Fe_0.5Nb_0.5)O₃ ceramics, dielectric constant and Qf value increased with La³⁺ content up to x = 0.03 due to an increase of density and grain size. Temperature coefficient of resonant frequency (TCF) was depended on B-site bond valence in single perovskite phase.