Energy Storage Performance Of Ba_6-3xLn_8+2xTi₁₈O₅₄?Ln=La,Nd? Linear Dielectric Ceramics

Dielectric capacitors possess highest power density among energy storage devices,and are widely used in pulsed power systems.However,the relatively lower energy storage density generally limits the development tendency of miniaturization and light weight in electric devices.In the present work,the dielectric properties,dielectric strength and energy storage density in Ba6-3xLn8+2xTi18O54(Ln = La,Nd)linear dielectric ceramics with new tungsten bronze structure have been systematically studied,and the effects of composition and microstructure on dielectric strength and energy storage density have been highlighted.The main conclusions are as following:Ba6-3xLa8+2xTi18O54(x = 0.5,2/3,0.75)ceramics are prepared by a standard solid-state method.The relative densities of all composition reach nearly 99%T.D.(theoretic density).With increasing x,the dielectric constant ?r,decreases from 113 to 102 gradually,but the dielectric strength increases from 682 kV/cm to 848 kV/cm.Meanwhile,microstructure has a significant influence on dielectric strength Eb and energy storage density U.Optimal Eb and U are obtained in ceramics with fine grains and low porosity for all three compositions.The highest energy storage density U ?3.2 J/cm3 is observed in ceramic of x= 0.75 sintered at 1375?,the dielectric strength of which reaches 848 kV/cm.The research on the morphology of breakdown channel indicates the thermal breakdown plays a dominant role in the dielectric breakdown process.The microstructure of Ba6-3xLa8+2xTi18O54(x?0.75)ceramic is further improved by spark plasma sintering(SPS).The grain size decreases obviously and the growth of columnar grains is suppressed.The dielectric constant ?r,decreases from 102(CS)to 85(SPS),since SPS sample is anisotropic.However,the dielectric strength increases from 848 kV/cm to 1058 kV/cm attributed to the improved microstructure of SPS sample.Finally,the energy storage density U reaches 4.2 J/cm3,which is 1.3 times of that in CS sample.What is more,the room temperature dielectric loss tan ? is lower than 0.002 in SPS sample.The dielectric constant ?r is stable at 81-87 in the temperature range of 30-350?,indicating Ba6-3xLa8+2xTi18O54 is a promising candidate in high temperature energy storage field.The energy storage characteristics in Ba6-3xNd8+2xTi18O54(x=0.25,2/3)ceramics are explored.The dielectric constant in this system is lower because the ionic radius of Nd3+ is smaller than La3+.When x = 0.25,the dielectric constant ?r = 95,the dielectric strength Eb = 522 kV/cm,and the energy storage density U= 1.1 J/cm3.When x = 2/3,the dielectric constant ?r = 87,the dielectric strength Eb = 837 kV/cm,and the energy storage density U = 2.7 J/cm3.Compared with La system,the ceramics of Nd system possess lower dielectric loss and better temperature stability,which makes it a candidate in energy storage field.