Design And Crystal Growth Of Complex Peroveskit Relaxor Ferroelectrics With High T_rt

Pb（Mg1/3Nb2/3）O3-PbTiO3（PMN-PT） complex perovskite structure relaxor ferroelectric single crystals were reported to possess ultrahigh piezoelectric coef?cient, dielectric permittivity and electromechanical coupling factor, making them one of the most promising candidates for medical ultrasonic imaging, sonar transducers and piezoelectric actuators, ect. However, the lower rhombohedral-to-tetragonal phase transition temperature T_rt limited its applications on piezoelectric-based high power transducers. The principle of end-member selection, the rule of MPB compositions designing, and the crystal growth of Relaxor-PT based ferroelectric materials were systematically investigated, to develop advanced high T_rt relaxor ferroelectric single crystal. Moreover, behavior of internal bias and its inner relationship with the electrical properties of Mn²⁺ doped Pb（In1/2Nb1/2）O3-Pb（Mg1/3Nb2/3）O3-PbTiO3（Mn:PIN-PMN-PT） were also studied, providing theoretical and experimental supporting for the development of new generation of high performance relaxor ferroelectric single crystals.By introducing non-PT end-member（s） with lower tolerant factor into the relaxor ferroelectric materials, combining the linear combination rule in complex peroveskit systems, two quaternary systems, PMN-PFN-PZ-PT and PMN-PIN-PZ-PT, were developed to explore the possiblility of increasing T_rt at MPB. XRD, Raman spectra and temperature dependence of dielectric permittivity were adopted to investigate the phase transition behaviors of the as-prepared ceramics, demonstrating both PIN and PZ benefitfed T_rt.PMN-PFN-PZ-PT and PMN-PIN-PZ-PT quaternary relaxor ferroelectric single crystals were grown for the first time through a slow cooling method. The d33, εr, Pr and Ec of（001）-cut 0.53PMN-0.10PFN-0.05PZ-0.32 PT single crystal were characterized to be 1250pC/N, 3540, 43.6μC/cm2 and 4.2kV/cm, respectively. The rhombohedral-tetragonal phase transition temperature T_rt was enhanced to 115 oC. The corresponding value of（001）-cut 0.456PMN-0.163PIN-0.053PZ-0.328 PT single crystal were 1500pC/N, 2165, 29.5μC/cm2 and 5.1kV/cm, respectively, with T_rt=100oC and Tc=181oC.A modified Brigman method was adopted to grow the novel quaternary relaxor ferroelectric single crystal with an opotimized composition of 0.324PMN-0.301PIN-0.055PZ-0.320 PT. The properties of（001）-cut single crystal with composition located at L position were characterized, exbiting high d33, εr, Pr and Ec of 1300pC/N, 5018, 35.1μC/cm2 and 4.7kV/cm, respectively. Of significant importance is that the T_rt of the as-grown crystal was as high as 130 oC, and the Tc increased to 199 oC.The origin of internal bias and its influence on peizoelectric coefficient, dielectric permittivity and mechanical quality factors in Mn²⁺ doped PIN-PMN-PT single crystals were further investigated. The value of internal bias was found highly dependent on the crystallographic orientations. Based on the investigation on piezoelectric and dielectric property at various internal biases, it was found that Mn²⁺ doping degraded both intrinsic and extrinsic contribution of them. Of particular significance was that, the piezoelectric coefficient and dielectric permittivity of the Mn²⁺ doped crystal still kept as high as 83% and 90%, respectively, of those of the nondoped ones. The mechanical quality factors were found to be improved variously from 20% to 300% after Mn²⁺ doping, depending on the crystallographic orientations, which was believed to be a closed relationship to the magnitude of internal bias and the polarization rotation angle: the larger value of them will result into higher mechanical quality factors.