Dielectric and piezoelectric properties of Pb (Zn_1/3Nb_2/3)O₃-PbTiO₃ single crystals

Single crystals of the relaxor ferroelectric solid solution family Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ (PZN-PT) have been shown to produce very high levels of electric field induced strains with large electromechanical coupling coefficients when poled along the <001> direction. These materials also exhibit a high dielectric permittivity and they are therefore very promising materials for transducer and actuator applications. We have carried out a systematic investigation of the dielectric and piezoelectric properties of different compositions, using specimens manufactured by TRS Ceramics Inc. Both the dielectric and piezoelectric strain responses of these crystals have been studied as a function of temperature and applied electric field. The applied field and temperature dependences of the rhombohedral to tetragonal and the tetragonal to cubic phase transitions have been determined. Our results suggest that a DC bias field can be used to stabilise the tetragonal phase. The strain measurements have been used to determine the d₃₃ values in both phases as a function of temperature. The PZN-PT crystals have their polar direction along the <111> axis but not much has been reported on the piezoelectric properties of crystals poled in this direction. We have used laser Doppler interferometry to measure the piezoelectric strains as a function of DC bias field applied in the <111> direction in PZN-PT crystals and we have determined values of the piezoelectric coefficients as a function of the DC bias field. High d₁₅ values over 3000 pC/N have been observed along <111> direction.