Effect of Sintering Temperature on the Ferroelectric Properties and the Electro-caloric Effect in Barium-Titanate Ceramics

BaTiO 3 ceramics were fabricated at various sintering temperatures by using a conventional solid-oxide reaction method. The ferroelectric properties and the electro-caloric effect (ECE) were investigated as functions of the sintering temperature. The sample had a low density (< 80% of the theoretical value) and a small grain size of about 1.5 µm when the sintering temperature was 1320 °C or lower whereas abnormal grain growth was observed at sintering temperatures above 1320 °C. The density and the matrix grain size increased significantly with increasing sintering temperature above 1320 °C. The P — E hysteresis loop of the sample showed a poor slanted-shape at 1320 °C and was well-saturated at sintering temperatures of 1350 °C and higher. The improvement in the P — E loop, which was obtained by increasing in the sintering temperature, might be caused by an increase in the matrix grain size or the appearance of abnormal grains. The maximum and the remanent polarizations decreased continuously with increasing measurement temperature from 60 °C to 160 °C. A constricted double-hysteresis P — E loop was observed at temperatures just above the Curie temperature (∼ 120 °C) due to an electric-field-induced phase transition. The adiabatic temperature change due to the ECE (Δ T ec ) was obtained using an indirect method. The maximum Δ T ec was obtained just above T c where the double P — E loop was observed. The sample sintered at 1365 °C showed the highest Δ T ec and EC strength ((∣Δ T ∣/∣Δ E ∣), which were 1.30 °C at 2 kV/mm and 0.65 K·mm/kV, respectively.