Growth And Melt State Of PT-based Relaxor Ferroelectric Crystals

Lead-based relaxor ferroelectric crystals with the compositions around the morphotropic phase boundary possess extraordinary have large piezoelectric constant, dielectric permittivity, electromechanical coupling coefficients, field-induced strain response and acousto-optic properties. There are promising applications in medical transducers, undersea applications and piezoelectric actuators. However, the application of binary system crystals at high temperature is limited because of the lower phase transition temperature. Fourthermore, the inhomogeneity of composition and properties is also important factor. At the same time, the relaxor mechanism of Pb-based ferroelectric single crystals need be discussed in detail. In the present work, the PSN modified PMN-PT single crystals are prepared by Bridgman method. The influence of PSN on electrical properties of PMN-PT single crystals is investigated. The chacteristics of resistance and temperature characteristics of PMN-PT single crystals are measured. The effect of temperature and frequency on dielectric relaxor behavior of PMN-PT single crystals is discussed.6PMN-61PMN-33PT crystals with the size of (?)25mm×55mm and (?)40mm×35mm are prepared by Bridgman method. The crystal structure, electrical properties, optical properties and their temperature ability are charactered. It is indicated that the phase structure of single crystals is peroviskite structure. The dielectric permittivity, coercive field and piezoelectric constant of crystals are 4060,6.18kV/cm and 1798pC/N, respectively. The infrared optical transmittance of the thickness of 0.3mm crystal wafer reaches up to 80%.The phase transition temperature of rhombohedral-tetragonal TR-T reachs up to 110℃. Compared with binary PMN-32PT single crystals, the comprehensive performances of ternary system PSN-PMN-PT are enhanced significantly.The electrical conductivity of PMN-32PT transforms from the insulator to the conductor with the increase of the temperature owing to its negative temperature coefficient of resistance. The resistance of PMN-32PT melt cannot reach a steady state at the corresponding temperature timely, which suggesting the PMN-32PT melt has a certain hysteresis. The resistance value of PMN-32PT melt are less than 100Ω in the temperature range of crystal growth, which reveals that the introduction of static magnetic field has the feasibility to control the free convection in the crystal growth.The dielectric relaxor behavior of PMN-32PT single crystals is described by the modified Curie-weiss law and Lorentz-type relationship. It is indicated that the diffuseness degree was dependent on the measured frequency and temperature. The diffuseness degree was enhanced with the increase of the measured frequency. It is believed that the dipole steering hysteresis was responsible for the improvement in diffuseness degree with the increase in measured frequency. Furthermore, the diffuseness degree was also varied with the increase of the temperature above Curie temperature. The main reason for the change of diffuseness degree with the measured temperature was attributed to the development of polarization of nanosize regions.