PIEZOELECTRIC PROPERTIES OF (BI1/2NA1/2)TIO3-BASED CERAMICS

Piezoelectric properties of bismuth sodium titanate, (Bi1/2Na1/2TiO3 (BNT)-based solid solution, (Bi1/2Na1/2)(1-x)(StaPbbCac)xTiO3(a +b+c=l) (BNTX [100x-100a/100 b/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, ktor k 33 (=50 %), along with a high mechanical strength. Acoustic wave characteristics of the BNIX[14–50/50/0], BNIX[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. © 1990, Taylor & Francis Group, LLC. All rights reserved.