ABSTRACT The temperature behavior of various relaxor-PT piezoelectric single crystals was investigated. Owing to a strongly curved morphotropic phase boundary, the usage temperature of these perovskite single crystals is limited by TR-T---the rhombohedral to tetragonal phase transformation temperature---which occurs at significantly lower temperatures than the Curie temperature Tc. Attempts to modify the temperature usage range of Pb(Zn1/3Nb2/3)O3--PbTiO3 (PZNT) and Pb(Mg1/3Nb2/3)O3--PbTiO3 (PMNT) rhombohedral crystals (Tc ∼ 150--170°C, TR-T ∼ 60--120°C) using minor dopant modifications were limited, with little success. Of significant potential are crystals near the morphotropic phase boundary in the Pb(Yb1/2Nb1/2)O3-PbTiO3 (PYNT) system, with a Tc > 330°C, even though TR-T was found to be only half that value at ∼160°C. Single crystals in the novel BiScO3--PbTiO3 system offer significantly higher Tcs > 400°C, while exhibiting electromechanical coupling coefficients k33 > 90% being nearly constant till the TR-T temperature around 350°C, which greatly increases the temperature range for transducer applications.
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