Ceramics-Silikáty 54 (3) 253-257 (2010)

SOLID STATE SINTERING PREPARED 0.935(Bi_0.5Na_0.5)TiO₃ -0.065BaTiO₃ LEAD-FREE CERAMICS: EFFECT OF SINTERING TEMPERATURE

H. Lidjici , M. Rguiti , F. Hobar , Ch. Courtois , A. Leriche

The effects of sintering temperature on structure, microstructure, dielectric and piezoelectric properties of 0.935(Bi_0.5 Na_0.5)TiO₃ -0.065BaTiO₃ (BNT6.5BT) lead free ceramics prepared by solid sintering technique at 1150-1200°C were investigated. The X-ray diffraction patterns showed that all of the BNT6.5BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. A fine and homogeneous grains were observed for samples sintered at 1150 and 1160°C and the increase of the sintering temperature up to 1180-1200°C induces significant grain growth with the appearance of coarse grains. The dielectric constant- temperature curves of the compositions exhibited strong dispersion with the increasing temperature, and the dielectric loss increased dramatically while the temperature over 230°C. The lowest value of depolarization temperature (T_d) was found at samples sintered at 1160°C. The values of remnant polarization P_r obtained at room temperature are 31 and 29 μC/cm₂ for specimens sintered at 1160°C and 1200°C respectively. At room temperature, BNT6.5BT ceramics sintered at 1180°C exhibited good performances: dielectric constant was 833 at 1 KHz, thick coupling factor k_t was 0.52 and the k_t/k_p ratio was 2.08. Therefore, the ceramics can be suitable for ultrasonic transducers in commercial applications.

Keywords: Lead-free ceramics, sintering temperature, dielectric and piezoelectric properties