Growth, Struction And Performance Of PMN-based Relaxor Ferroelectric Crystal

Pb(Mgi/3Nb2/3)O3(PMN)-based relaxor ferroelectric crystals have been widely applied in the field of medical imaging, transducer and ultrasonic motor due to the high dielectric, piezoelectric, pyroelectric properties, and high electrostriction. However, the PMN-xPT crystals are easily depoled under the high electric field because of the low coercive field, which is limited to their applications in high-power transducers. In addition, the crystals are considered as the multifunctional materials, the poor optical properties are significantly influence of the application on opto-coupled isolators, such as fluorescence imaging and upconversion laser. Therefore, PMN, PMN-32PT and Er3+ doped PMN-32PT were grown. The growth mechanism, structure, electrical properties and optical properties were investigated, and the mechanism for down and up conversion luminescence properties was discussed. The results were showed as follows:The PMN single crystals were grown by using the flux method. The pure perovskite structure was found in the as-grown crystals. The flat surface and growth step were observed, and the exposed face was the {100} crystal planes. The fastest growth rate of PMN single crystals was the [111] face, followed [110] and [100].The electrical conductivity of PMN-32PT melts was measured in the high temperature and the process of crystals growth, the resistance was less than 200 Ω. The dielectric permittivity, loss, piezoelectric coefficient and coercive field of PMN-32PT single crystal were 4056,0.023, 1072 pC/N and 5.22 kV/cm, respectively.Er3+ doped the PMN-32PT crystals were grown by using the flux method, the optical properties of the PMN-32PT crystals were improved. The dielectric permittivity, and piezoelectric coefficient of as-grown crystals were 4300 and 1210 pC/N, respectively. The coercive field was 6.37 kV/cm, which was obviously higher than the pure PMN-32PT crystals. Furthermore, the stronger dielectric relaxation characterization of those crystals were found, the degree of the phase transition was drastically enhanced with the increase of the measuring frequency, which was ascribed to the change of polar region by the modification of Er3+ions. The infrared transmittance of crystal was found to be about 68%. The down and up conversion were obtained under the excitation wavelength of 491 nm,800 nm, and 980 nm, the fluorescence intensities under 980 nm enhanced with the excitation power increasing. The mechanism for the upconversion are two-photo excitation and cooperative upconversion.