Dielectric and piezoelectric properties of 0.93Pb(Zn 1/3 Nb 2/3 )O 3 –0.07PbTiO 3 (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, T rt , 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, T c , 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, k 33 ' , of PZNT 93/7 SC was 84% at room temperature, which is as large as that of PZNT 91/9 SC. The k 33 ' value of PZNT 93/7 SC hardly changed up to about 100°C and then decreased gradually towards the Curie temperature, T c . The degradation temperature of the k 33 ' value was roughly in agreement with the phase-transition temperature, T rt , 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 T rt is thought to be important for guaranteeing a high k 33 ' value and minimum dielectric hysteresis. PZNT 93/7 SC with a reduced Ti content had not only a higher T rt 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.
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Hosono et al. (2002) studied this question.