Dielectric and Piezoelectric Properties of 0.93Pb(Zn_1/3Nb_2/3)O₃–0.07PbTiO₃Piezoelectric Single Crystals for Medical Array Transducers

Abstract

Dielectric and piezoelectric properties of 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 (PZNT 93/7) piezoelectric single crystals (PSC) have been investigated. The PZNT 93/7 single crystals (SC) with diameters of 40 mm were grown successfully by the Bridgman method with PbO flux. The dielectric constant of PZNT 93/7 SC at room temperature was about 3500, which is slightly larger than that of PZNT 91/9 SC. Phase-transition temperature, Trt, of PZNT 93/7 SC was 108°C, which is about 40°C higher than that of PZNT 91/9 SC; however, the Curie temperature, Tc, of PZNT 93/7 SC was 170°C, which is about 10°C lower than that of PZNT 91/9 SC. The coupling factor of rectangular bar mode, k33', of PZNT 93/7 SC was 84% at room temperature, which is as large as that of PZNT 91/9 SC. The k33' value of PZNT 93/7 SC hardly changed up to about 100°C and then decreased gradually towards the Curie temperature, Tc. The degradation temperature of the k33' value was roughly in agreement with the phase-transition temperature, Trt, from the rhombohedral to tetragonal phase, measured using the poled PZNT SC. Moreover, no dielectric hysteresis was observed in PZNT 93/7 SC in the temperature range from 0°C to 80°C, although a dielectric hysteresis was observed in PZNT 91/9 SC in the same temperature range. Therefore, the Trt is thought to be important for guaranteeing a high k33' value and minimum dielectric hysteresis. PZNT 93/7 SC with a reduced Ti content had not only a higher Trt but also its piezoelectric properties were as good as those of PZNT 91/9 SC near the morphotropic phase boundary (MPB). Therefore, PZNT 93/7 SC achieves the optimum balance of piezoelectric properties and their thermal stability for certain applications performed at comparatively high temperatures.