Preparation And Electrical Properties Of Sodium Niobate Based Lead-free Antiferroelectric Ceramics

Dielectric capacitors have the advantages of fast charge and discharge rate,high power density and good temperature stability,etc.They are widely used in the fields of new energy vehicles,medical laser and military industry.With the continuous development of 5G technology,electronic components are gradually becoming thinner,diversified and miniaturized,which puts forward higher requirements for the energy storage density of dielectric capacitors.Sodium niobate（NaNbO₃,abbreviated as:NN）has high Curie temperature and high polarization strength,and is a very promising lead-free antiferroelectric energy storage material.However,pure NN ceramics have a large remanent polarization,and it is difficult to obtain a high energy storage density.In addition,the use of conventional high-temperature sintering technology can easily cause coarse crystal grains,weaken its electrical properties,and cause a large amount of energy loss.Therefore,how to further increase the energy storage density of NN ceramics and reduce the sintering temperature has become the focus of current research.In this paper,NN ceramic is taken as the research object.On the one hand,the energy storage density can be increased by adjusting the composition and microstructure.On the other hand,the cold sintering process of NN ceramics was explored,and the effects of low temperature sintering on its microstructure and electrical properties were investigated.（1）Using the regulation strategy of reducing the tolerance factor of the system,Ca Zr O₃（abbreviated as:CZ）was introduced into the NN system to decrease remanent.The research results show that a certain amount of CZ can enter the NN crystal lattice,effectively stabilizing the antiferroelectric phase.At the same time,a small amount of the second phase Zr O₂is attached to the edge of the grain boundary,which can be used as a grain growth inhibitor to refine the grains and reduce the grain size from 5.35μm to 2.82μm.When the CZ content is 14 mol%,the highest electric field is 370 k V/cm,the recoverable energy storage density is 3.0 J/cm³,and the energy storage efficiency is 85.3%.In addition,it also exhibits good temperature and frequency stability.The above results indicate that CZ-doped NN ceramics are very promising lead-free dielectric energy storage materials.（2）Taking 0.86NaNbO₃-0.14Ca Zr O₃as the research object,Mn O₂was introduced as a sintering aid to form a liquid phase at high temperature to promote ceramic sintering,and its microstructure and energy storage performance were systematically investigated.The research results show that Mn O₂does not change the crystal structure of ceramics,but can significantly reduce the sintering temperature,increase density and reduce the leakage current.When the optimal component Mn O₂content is 0.50 mol%and the highest electric field is 430 k V/cm,excellent energy storage performance can be obtained（the recoverable energy storage density is 3.6 J/cm³and the energy storage efficiency is 91.9%）,which provides research ideas for improving the energy storage characteristics of lead-free dielectric materials.（3）In order to solve the problems of Na volatilization and coarse grains caused by high temperature sintering of NN ceramics,cold sintering process was used to prepare high-quality NN ceramics,and the phase structure,microstructure and electrical properties were systematically investigated.The research results show that the density of the ceramic green body is 92.6%after cold sintering process,and the high-density ceramic obtained after post-heat-treatment at 1230℃ has a relative density of 96.9%and a grain size of 3.65μm.The relative density of NN ceramics prepared by conventional sintering method at 1300℃ is 93.5%,and the grain size is 6.95μm.In addition,the polarization strength of NN ceramics prepared by cold sintering process and post-heat-treatment at 1245℃ up to 34.2μC/cm².