Energy Storage Properties Of Tetragonal Tungsten Bronze Niobate Glass Ceramics

With the development of science and technology,some frontier or cutting-edge technical fields hope that the pulse power system can have a higher level.In order to improve the integration of pulse power system and conform to the trend of miniaturization,some materials with high energy storage density are urgently needed as dielectric materials of pulse power capacitor.Tetragonal tungsten bronze glass ceramics,as a new type of linear dielectric material,has the advantages of high dielectric constant,high breakdown strength,low loss and high energy storage density.It is a potential dielectric material for energy storage capacitors.In this thesis,Na-Sr-Nb-Si-based glass ceramics were selected as the research materials,and the effects of crystallization temperature,sample thickness,Ca and Mg doping on the energy storage properties of the glass ceramics were investigated from the aspects of crystal phase composition,micro morphology and crystallization behavior.There are two competing mechanisms for the effect of crystallization temperature on the energy storage properties of Na-Sr-Nb-Si-based glass ceramics:with the increase of crystallization temperature,the dielectric constant of the glass ceramics first increases and then decreases;high temperature destroys the glass grid and reduces the number of grain boundaries per unit thickness,resulting in the decrease of breakdown strength.With the increase of crystallization temperature,the energy storage density of Na-Sr-Nb-Si-based based glass ceramics increases first,reaches the peak value and then decreases gradually.When the crystallization temperature is 1175℃,the maximum energy storage density of Na-Sr-Nb-Si-based glass ceramics is 1.44 J/cm~3.The thicker the sample is,the more defects and pores there are,and the easier avalanche multiplication occurs.Therefore,the thinning can effectively increase the breakdown strength of Na SR NB Si based glass ceramics.In this thesis,hydrofluoric acid etching method was used to thin the glass ceramics to 100μm.the breakdown strength and energy storage density of the Na-Sr-Nb-Si-based glass ceramics at 100μm are 456.0 k V/cm and 4.87 J/cm~3,which are 1.78 and 3.38 times of the unthinned samples(400μm thick),respectively.In this thesis,Ca and Mg are introduced as nucleating agents to inhibit the crystallization behavior of Na-Sr-Nb-Si-based glass ceramics.Although the lower crystallinity leads to the decrease of the dielectric constant of the glass ceramics,the breakdown strength of the glass ceramics is increased,thus the energy storage density is increased.Under the test frequency of 1 k Hz,the maximum energy storage density of glass ceramics is 3.03 J/cm~3 when the Ca doping concentration is 3%,the crystallization temperature is 1000℃,and the thickness is 400μm,which is 2.1 times of that of undoped samples;the maximum energy storage density of glass ceramics is 2.94 J/cm~3 when the Mg doping concentration is 3%,the crystallization temperature is 1100℃,and the thickness is 400μm,which is 2.04 times of the energy storage density of undoped samples.After that,the Ca and Mg doped Na-Sr-Nb-Si-based glass ceramics were further thinned.It is found that the energy storage density of Ca and Mg doped glass ceramics can be effectively improved by thinning.When the thickness of glass ceramics decreases to 100μm,the maximum energy storage density of Mg doped samples increases from 2.94 J/cm~3to 7.36 J/cm~3,which is 150%,and that of Ca doped samples increases from 3.03 J/cm~3 to8.06 J/cm~3,which is 166%.