The Study Between Structure And Dielectric Properties Of SrTiO₃-MgO Ceramics

The properties of dielectric ceramics significantly depend on micro-structure and electrical structure. At present, SrTiO3ceramic is excellent candidate for store energy application, however, the relationship is rarely reported and not clear among micro-structure, electrical structure and dielectric properties. Therefore, SrTiO3ceramics were chosen and the following work were carried out:(1) The SrTiO3+xwt%MgO composite ceramics (x=0,0.5wt%,1.0wt%,4.0wt%,10.0wt%,20.0wt%) have been synthesized by solid state reactions, and the phase structures, micro-structure, electrical structure and dielectric properties of composite ceramics have been analysized. X-ray diffraction patterns show a single SrTiO3phase when x<1.0wt%, and show the composite ceramics with perovskite SrTiO3phase and cubic halite-structured MgO phase with x>1.0wt%. With increasing the content of MgO, the grain size and room temperature dielectric constant of ceramics decrease, and the dielectric loss is less than0.003. It is show by SEM testing that the MgO phase exits in the triangle grain boundary formed by SrTiO3grain. The dielectric relaxor in ceramics is related to the Maxwell-Wagnerr interface polarization, and the mechanism of relaxation has been changed by MgO incorporating.(2) The electrical structures of ceramics are made up by grain and grain boundary, which have different conductivity, and the insulative performance of ceramics mainly come from the region of grain boundary. The conductivity activation behavior of grain in x=0ceramic is dominated by the diffusion of oxygen vacancy. When x>0, the conductivity activation behavior of grain is governed by the second ionization of oxygen vacancy. With increasing the content of MgO, the conductivity activation energy of grain boundary decrease, and then increase. The maximum energy storage density obtained the highest breakdown strength (BDS) of ceramic is197.30kV/cm is0.89J/cm3, when the low conductivity activation energy of grain boundary in x=1.0wt%ceramic.(3)Due to the result of ceramics prepared by solid state reaction, the SrTiO3+xwt%MgO composite ceramics (x=4.0wt%,10.0wt%) have been synthesized by powder coated using sol-gel method. TEM shows the powder of SrTiO3has been coated by MgO. The grain size of ceramics is smaller than the grain size of ceramics using solid state reaction, less than1μm. It is found that the difference of electrical structure between SrTiO3phase and MgO phase have been improved, the conductivity activation energy of grain boundary decrease, and the store energy properties has been enhanced. When x=4.0wt%, the store energy density is0.82J/cm3with the BDS209.37kV/cm.