Pyroelectric properties of calcium doped strontium barium niobate ceramics Sr_0.65−xCa_xBa_0.35Nb₂O₆ (x = 0.05–0.425)

Calcium-doped strontium barium niobate ceramics Sr_0.65−xCa_xBa_0.35Nb₂O₆ (SCBN, 0.05 ≤ x ≤ 0.425) were prepared by solid state reaction method. From the X-ray diffraction patterns and Raman spectra, it was found that calcium was completely dissolved into the tetragonal tungsten-bronze (TTB) crystal structure upto x = 0.20, above which second phase CaNb₂O₆ (CN) was formed. Diffuse phase transitions was observed in all the samples. The Curie temperature of the SCBN ceramic was increased from 60 to 103 °C with the calcium dopant. Frequency (2–200 mHz) and temperature (25–110 °C) dependence of the pyroelectric coefficient were measured. From the frequency profile of the pyroelectric coefficient, the thermal diffusivity was determined. Due to the low Curie temperature, all samples experienced serious thermal depolarization and the pyroelectric coefficient was greatly decreased during the cooling round. The sample with x = 0.125 shows the largest pyroelectric coefficient of 237 µC/m²k. The piezoelectric coefficient (d₃₃) was also increased after calcium doping.