Piezoelectric properties of bismuth sodium titanate ceramics

The Bi-excess bismuth sodium titanate ceramics, BNT+Bi(2)O(3)x wt% [BNT-x], and hot-pressed (HP) BNT ceramics were prepared and investigated as aiming to estimate true piezoelectric properties of the BNT ceramic. An electromechanical coupling factor, k(33), and piezoelectric constant, d(33), of the BNT-0.3 ceramic sintered at 1225degreesC for 30 min were estimated to be 0.47 and 93 pC/N, respectively. That was measured by means of a resonance-antiresonance method after the poling. BNT-x (x = 0-2.0 wt%) ceramics were prepared by means of a conventional ceramic fabrication technique and sintered at 1225degreesC for 5 min - 100 h. All of BNT-x ceramics showed a high density-ratio of more than 95% to an observed/theoretical density. A resistivity, rho, of the BNT-0.3 ceramic shows the largest value of about 10(14) Omega-cm. While, k(33), and d(33), of the HP-BNT-0 ceramic prepared at 1100degreesC for 30 min with a pressure of 200 kg/cm(2) were 0.48 and 98 pC/N, respectively. From the thermograph (TG, Weight loss) measurement, the weight loss caused by the Bi vaporization was carried out at a temperature above 1130degreesC. It is thought that the suppression of Bi vaporization is the reason why the relatively large and true k(33) values were obtained for HP-BNT ceramic sintered at 1100degreesC without Bi vaporization.