Study On Grain Boundary Structure And Domain Structure Of Perovskite Plus Energy Storage Dielectric Materials

The dielectric materials are widely used in energy storage capacitors of various pulse power equipment due to their excellent performance.The pulse power system requires that the energy storage materials have the advantages of high release efficiency,low dielectric loss,and small charges and discharges speed.The SrTiO₃?STO?-based dielectric materials have been extensively studied for their special physical properties.Based on the STO-based dielectric materials,the grain boundary and domain structure were systematically studied by experiments and simulations.The relaxed perovskite?Sr,Pb,Bi?TiO₃?SPBT?dielectric ceramics have a low remnant polarization,a high release efficiency and a low dielectric loss.The substitution at the A site may have a significant impact on the properties of the materials due to the STO-based materials are very sensitive to the impurities.In this experiment,La-doped SPBT ceramics were prepared by the solid-state method.The transmission electron microscope?TEM?was used to study the grain boundary of the La-doped SPBT dielectric material,and it shows that the microdomain structure near the grain boundary.The atomic force microscopy?AFM?results show that the La³⁺doping is prompted the microdomains to grow.The appearance of microdomains near the grain boundaries reduces the distortion energy of the materials and enhances the relaxation properties.The dielectric materials have a high energy release efficiency of 98.6%and a minimum of approximately 0.03%dielectric loss due to a low pinning effect under a high electric field.Based on the data of the grain boundary structure,a theoretical grain boundary model was established in VASP.The specific structure and properties of the grain boundary model were calculated.The grain boundary energy of the doped random grain boundary is higher than the symmetrical one.The Pb doping causes charge transfer on both sides of the grain boundary,with the charge transfer centers exist at the grain boundary.In the case of the Pb-doped and non-stoichiometry with Ti:O ratio at the grain boundaries,the donor band characteristic develops at the low energy edge of the conduction band,the Fermi level is within the conduction band,reflecting the fact that the electrons content of the conduction band increases.The excess electrons are localized over the Ti atoms,so that some Ti atoms are reduced to Ti³⁺,and the grain boundaries are semiconducting.The XPS results show that 64%of the Ti atoms in the breakdown region of the sample changed from Ti⁴⁺to Ti³⁺,corresponding to the simulation results.The three-dimensional domain structure of?1-x?SPBT-xLa₂O₃ceramics was synthesized by MATLAB.It is clear that the direction of the domain structure is connected head to tail near the grain boundaries.The ferroelectric displacement distortion results of the grain boundary model are corresponding to the experiment results.The domain wall with head to tail has the same potential and current as of the bulk.This domain wall structure easily forms a natural leakage current channel at the grain boundary.