Understanding the microwave dielectric properties of (Pb0.45Ca0.55)[Fe0.5(Nb1−xTax)0.5]O3 ceramics via the bond valence

Microwave dielectric properties of the (Pb0.45Ca0.55)[Fe0.5(Nb1−xTax)0.5]O3 ceramics were investigated in the range of 0.0⩽x(mol)⩽1.0. With increasing Ta2O5, the dielectric constant and the temperature coefficient of the resonant frequency (TCF) decreased, while the Q·f value of the specimens increased. The change of dielectric constant was evaluated by the correlation between ionic polarizability and bond valence. TCF of the specimens decreased with the tilting of oxygen octahedra due to an increase of bond valence of the B-site. The Q·f values were studied by infrared reflectivity spectra from 50 to 4000 cm−1, and calculated by the Kramers-Kronig analysis and classical oscillator model. The specimens with 0.4 mol of Ta2O5 sintered at 1150 °C for 3 h showed εr of 82, Q·f of 7650, and TCF of −5 ppm/°C.