Piezoelectric properties of (Bi1/2Na1/2)TiO3-based ceramics

Abstract

Abstract Piezoelectric properties of bismuth sodium titanate, (Bi1/2Na1/2)TiO3 (BNT)-based solid solution, (Bi1/2Na1/2)(1−x)(St a Pb b Ca c ) x TiO3(a+b+c=1)(BNTX [100x−100a/100b/100c]), are studied as a new substrate material group of lead- free or low lead content piezoelectric ceramics. A rhombohedral (Fα)-tetragonal (Fβ) morphotropic phase boundary (MPB) is shown to exist at x =0.13 by X-ray diffraction data. BNTX ceramics are superior for piezoceramics in high frequency ultrasonic uses, with a lower free permittivity, ϵ33T/ϵ0 (=240 ∼ 340) and a high electromechanical coupling factor, k t or k 33 (=50%), along with a high mechanical strength. Acoustic wave characteristics of the BNTX[14-50/50/0], BNTX[13-0/75/25], and BNTX[1-0/0/100] demonstrate that the ceramics are a new substrate material group for a surface acoustic wave and/or a bulk acoustic wave. Two interdigital transducers can excite an SH plate mode wave whose travelling direction is perpendicular to the poling axis along to the substrate width. A delay line type oscillator using the SH wave is shown to have a single mode oscillation of about 8 MHz.