Preparation And Properties Of Barium Strontium Titanate/Zirconia Composite Materials

In this paper,the composite material of barium strontium titanate(BST)/zirconia(ZrO2)was investigated in order to develop the optical,dielectric and ferroelectric application based on BST system.Using rare earth La or alkaline earth Mg as the dopant,the photoluminescence properties of BST and BST/Zr02 powders were studied.The dielectric properties and the energy storage properties of both BST ceramics with dopant and the composite ceramics were also studied in detail.The main work of the paper is as follows.Firstly,barium strontium titanate powders were prepared by a sol-gel method.Zirconia nanopowders were prepared by a liquid-phase precipitation process.The composite powders of BST/ZrO2 were prepared by the method of sol-gel combined liquid-phase precipitation process.Secondly,the effects of La doping on the photoluminescence properties of both BST powders and BST/ZrO2 composite powders were studied.By 370 nm excitation,the emission peaks of La-doped composite powders at 405,458,615 nm are observed,and the luminescence is in the white light region.Also the effects of Mg doping on the photoluminescence properties of BST powders and BST/ZrO2 composite powders were studied.The results show that Mg dopant cannot stimulate the luminescence behavior when the A-site of BST is substituted by Mg2+;however,when the B-site of BST is substituted by Mg2+,the broad emission occurs at the range of 413 to 450 nm,and the luminescence is in the blue light region.For Mg-doped composite powders,the emission peaks are at 405 nm and 615 nm when by 368 nm excitation,and the emission light is in the white light region.Furthermore,the effect of sintering temperature on the electrical properties of intrinsic BST ceramics and the BST/ZrO2 composite ceramics were studied.The influence of La doping or Mg doping on the electrical properties and energy storage properties of ceramics was investigated in detail.For the intrinsic BST ceramics and the BST/ZrO2 composite ceramics,compared to the samples sintered at different temperatures,the dielectric constant reaches the largest value sintered at 1400?.Sample has the smallest dielectric loss sintered at 1450?,and the temperature stability of dielectric properties is the best in the range of-20? to 80?.For La-doped ceramic samples,compared to the samples sintered at different temperatures,the dielectric constant of ceramics sintered at 1400? reaches the highest value;however the ceramic dielectric loss of samples sintered at 1350? is the smallest,and the ceramic samples are with the best temperature stability of dielectric properties.La doping cannot improve the dielectric constant of ceramics,but it can effectively improve its dielectric loss-temperature stability at the range of-20? to 80?.When the doping concentration is 2%La,BST ceramics have the relatively high dielectric constant.When the doping concentration is 4%La,the dielectric loss of BST ceramics is the smallest.La doping leads to an increase of the leakage current.In this La doped BST system,the dielectric constant of ceramics can be increased by coated zirconia.With coated zirconia,the ceramic dielectric loss is reduced,and the ceramic dielectric loss-temperature stability is also improved.More important,zirconia reduces the leakage current of composite ceramics.In particular,the energy storage density of BST ceramics is significantly improved.For the samples of ceramics sintered at 1300? with 4%La,the measured energy storage density(at 43 kV/cm)increases from 5.640 10-3 to 24.532 10-3 J·cm-3 by coated zirconia.For Mg-doped ceramic samples,the ceramic dielectric constant reaches the highest when sintered at 1200?,and the samples have good dielectric-temperature properties.The dielectric loss of ceramics sintered at 1250? is low,with the good temperature stability.Although Mg doping does not improve the dielectric constant of the ceramics,it can reduce the dielectric loss.Also its temperature stability is improved in the range of-20? to 80?,and the leakage current is reduced.In this system,zirconia has no significant improvement for dielectric constant and dielectric loss,but it can reduce the leakage current.Especially,the energy storage density of barium strontium titanate ceramics improve significantly by coated zirconia.For the ceramics sample of 4%Mg doping sintered at 1150?,its measured energy storage density(at 38 kV/cm)increases from 4.297 10-3 to 18.478 10-3 J·cm-3 by composing with zirconia.