Influence Of External Field On Domain And Properties Of The Oriented Ferroelectric Materials

As an important functional material, ferroelectric materials have been widely used in microelectronics and micro-mechanical systems. Recently, the research on ferroelectric materials has become a hot. The ferroelectric properties are affected by crystallization, orientation etc. The orientation plays an important role in improving electrical properties. To further improving ferroelectric properties, the oriented ferroelectric materials are drawing more and more attention. Relaxation single crystal and textured ceramics are always the two main structure system in the ferroelectric material.In this thesis, the textured BaTiO3 ceramics were prepared by the template grain growth (TGG). The influences of external field on properties of textured ceramics were investigated. The variation of ferroelectric domain in different oriented PMN-32PT single crystal was observed by polarization microscope, and the effects of external field on properties of PMN-32PT single crystal were also discussed. The results are as follows:1) Textured BaTiO3 ceramics are successfully prepared by template grain growth. The piezoelectric constant Of the textured BaTiO3 ceramic reaches to 129 pC/N.2)A dispersive phase-transition behavior was observed according to the dielectric-tempe-rature spectrum. Compared with commercial material BaTiO3 ceramics, the equiaxial BaTiO3 ceramics and textured BaTiO3 ceramics display decrease in diffuseness. The Curie temperature of textured ceramics slightly decreases compared to that of equiaxial BaTiO3 ceramics. However, the dielectric constant of textured ceramics obviously decreases.3) BaTiO3 ceramics show excellent dielectric nonlinearity and high dielectric constant under DC bias electric field. With DC bias increases, the dielectric constant decrease. With DC bias variation, the phase-transition temperature of equiaxed-BaTiO3 ceramic varies obviously, but the phase-transition temperature of textured BaTiO3 ceramic almost dose not change.4) In [100]cub-oriented PMN-32PT single crystal, the form and moving of new domain are related to electrodes in DC electric field. Paralleling to electric field direction, domains grow faster than that perpendicular to the electric field. Under the AC electric field, the vibration frequency of domain wall is much lower than AC frequency for PMN-32PT single crystal, which indicates the relaxation characteristics of PMN-32PT single crystal.5) A hysteresis was observed in the paraelectric-ferroelectric phase transition of PMN-32PT single crystal. The nucleation undercooling of ferroelectric phase in paraelectric phase is about 5℃.6) The mechanical property of PMN-32PT single crystal has been firstly measured by DMA analysis, the change of elastic modulus with T is find to be similiar to that of s with T and they also have the same phase transformation process.