Microstructure, structural defects, and piezoelectric response of Bi4Ti3O12 modified by Bi3TiNbO9

Microstructure, structural defects, and piezoelectric response of bismuth t itanate (Bi4Ti3O12)(1-x) and bismuth titanium niobate (Bi3TiNbO9)(x) solid solution with x=0.05 and 0.2 were investigated. Depending on x and on the s intering temperature different microstructures and piezoelectric responses were observed. For a low content in Bi3TiNbO9 (x=0.05) and a high sintering temperature (1130 degreesC), a coarse grain size is present, the number of structural defects within the grain is small, and there is a strong depend ence of d(33) on the ac pressure. For higher Bi3TiNbO9 (x=0.2) content or f or lower sintering temperature (1080 degreesC) and x=0.05, the grain size i s finer and a large number of structural defects is present within the grai ns. In particular, for x=0.2, high resolution transmission electron microsc opy shows a high concentration of intergrowth defects which consist of Bi3T iNbO9 layers inserted in the Bi4Ti3O12 matrix in a more or less random way. In these samples, there is a very small dependence of d(33) on the ac pres sure and the piezoelectric hysteresis is likewise very small. The relation between microstructure and piezoelectric properties is discussed and it is shown that there is a good correlation between the dependence of the piezoe lectric response on the ac pressure and the defect density. The piezoelectr ic response may be related to the structural defects present within the gra in. (C) 2000 American Institute of Physics. [S0021- 8979(00)04801-0].