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

BaTiO3 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 mu m when the sintering temperature was 1320 degrees C or lower whereas abnormal grain growth was observed at sintering temperatures above 1320 degrees C. The density and the matrix grain size increased significantly with increasing sintering temperature above 1320 degrees C. The P - E hysteresis loop of the sample showed a poor slanted-shape at 1320 degrees C and was well-saturated at sintering temperatures of 1350 degrees 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 degrees C to 160 degrees C. A constricted double-hysteresis P - E loop was observed at temperatures just above the Curie temperature (similar to 120 degrees C) due to an electric-field-induced phase transition. The adiabatic temperature change due to the ECE (Delta Tec) was obtained using an indirect method. The maximum Delta Tec was obtained just above Tc where the double P - E loop was observed. The sample sintered at 1365 degrees C showed the highest Delta Tec and EC strength (( divide Delta T divide / divide Delta E divide ), which were 1.30 degrees C at 2 kV/mm and 0.65 K center dot mm/kV, respectively.