DIELECTRIC AND PIEZOELECTRIC PROPERTIES OF 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 PIEZOELECTRIC SINGLE CRYSTALS FOR MEDICAL ARRAY TRANSDUCERS

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 by the Bridgman method with PbO flux. The dielectric constant of PZNT 93/7 SC at RT 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 RT, 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 to 80 C, although a dielectric hysteresis was observed in PZNT 91/9 SC in the same temperature range. Therefore, the Trt 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. PZNT 93/7 SC achieves the optimum balance of piezoelectric properties and their thermal stability for certain applications performed at comparatively high temperatures. 12 refs.