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

The microwave dielectric properties of the (Pb0.45Ca0.55)[Fe0.5(Nb1-xTax)0.5]O3 ceramics were investigated in the range of x = 0.0-1.0. With increasing Ta2O5, the dielectric constant and temperature coefficient of resonant frequency (TCF) decreased, while the Q factor of the specimens increased. The change of dielectric constant was evaluated by the correlation between ionic polarisability and bond valence. TCF of the specimens decreased with the tilting of oxygen octahedra due to increasing bond valence at the B-site. The Q factor values were studied by IR reflectivity spectra from 50 to 4000 cm-1, and calculated by the Kramers-Kronig analysis and classical oscillator model. Specimens with 0.4 mol of Ta2O5 sintered at 1150 C for 3 h showed a dielectric constant of 82, Q factor of 7650, and TCF of -5 ppm/C. 16 refs.