Structural phase transition and physical properties of tetragonal 0.85Pb(Zn1/3Nb2/3)O3–0.15PbTiO3 single crystals

Abstract

Large-size and high-quality 0.85Pb(Zn1/3Nb2/3)O3–0.15PbTiO3 (0.85PZN-0.15PT) single crystals were grown by a modified Bridgman method using an allomeric 0.69Pb(Mg1/3Nb2/3)O3–0.31PbTiO3 single crystal as a seed. The as-grown 0.85PZN-0.15PT single crystals exhibit a tetragonal perovskite structure, which changes wholly into a cubic structure between 190 and 215 °C confirmed by high-temperature x-ray diffraction measurement. 0.85PZN-0.15PT exhibits sharp dielectric-response peaks with slight dielectric frequency dispersion where the ferroelectric-paraelectric phase transition is nearly first order. Polarization induces an additional dielectric anomaly around 147 °C accompanied by the increase in Curie temperature (TC), the decrease in the value of dielectric maximum (εm), and the enhancement of frequency dispersion, which can be assigned to the orientation of a ferroelectric domain or a macro-micro domain transition upon heating. The [001]-oriented 0.85PZN-0.15PT crystal planes exhibit excellent electrical properties, where remanent polarization Pr is 58.27 μC/cm2 and piezoelectric constant d33 is around 530–570 pC/N. Pyroelectric coefficient p, detectivity, and voltage responsivity figures of merit Fd and Fv of the 0.85PZN-0.15PT single crystals are 460 μC/K m2, 13.14 μPa−1/2, and 0.0302 m2/C, respectively, which increase greatly over the temperature range measured. It is needed to improve the temperature stability and the voltage responsivity to meet the requirements of practical applications. 0.85PZN-0.15PT exhibits rather high transparency, with the ultraviolet cut-off edge near 380 nm indicating a low-lying electronic energy gap of ∼3.16 eV. The infrared-absorption band occurs at 597 cm−1, which can be attributed to the normal vibration of the [Zn1/3Nb2/3]/TiO3 group.