Preparation And Dielectric Properties Of Ba_0.6Sr_0.4Ti_0.7Zr_0.3O₃ Based Dielectric Ceramic

Barium strontium zirconate titanate(Ba_xSr_1-xTi_yZr_1-yO₃)dielectric ceramics have received a lot of attention due to its excellent dielectric properties.For example,the sample of Ba_0.65Sr_0.35Ti_0.65Zr_0.35O₃ has a superior dielectric constant（5000）and low Curie temperature（-113℃）,but its high sintering temperature（1500℃）and difficult sintering of Ba_0.65Sr_0.35Ti_0.65Zr_0.35O₃ ceramic,which restricts its extensive application in business.In recent years,the Bi-based perovskite-structured Bi（Me）O₃（Me represents trivalent metallic ions）has been introduced into the BT-based ceramic,and this can reduce the sintering temperature and improve the temperature stability of the dielectric permittivity of BT-based ceramics.The operating temperature range of the device is greatly improved.In this work,（1-x）Ba_0.6Sr_0.4Ti_0.7Zr_0.3O₃-x Bi(Li_0.5Ta_0.5)O₃（x=0,0.10,0.15,0.20）dielectric ceramics were synthesized and prepared by solid-state reaction method combined with conventional sintering using the idea of doping Bi（Me）O₃.Specifically,for x=0,0.10,0.15 and 0.20,the samples of（1-x）Ba_0.6Sr_0.4Ti_0.7Zr_0.3O₃-x Bi(Li_0.5Ta_0.5)O₃were sintered in air at 1500℃、1300℃、1200℃ and 1150℃ for 8 h,respectively.The sintering temperature of Ba_0.6Sr_0.4Ti_0.7Zr_0.3O₃ decreased with the increase of Bi(Li_0.5Ta_0.5)O₃（BLT）content,indicates that the addition of BLT is beneficial to reduce the sintering temperature of BSTZ.The X-ray diffraction combined with XRD refinement results showed that（1-x）Ba_0.6Sr_0.4Ti_0.7Zr_0.3O₃-x Bi(Li_0.5Ta_0.5)O₃ were all pseudo-cubic structure,and there was no secondary phase in whole compositional range.Moreover,the relative density of the samples reached 93～95%.The average grain size of（1-x）BSTZ-x BLT is 1.74～2.67μm,and the individual elements of all components are uniformly distributed.The critical electric field corresponding to the saturation polarization intensity of BSTZ increases from 70 k V/cm to 90 k V/cm when BLT increases from x=0 to x=0.10.Due to the 0.90BSTZ-0.10BLT have small average grain size（AGS）,and the small grain size is favorable to enhance the electric field used in dielectric ceramics.The dielectric constants of 0.85BSTZ-0.15BLT and 0.80BSTZ-0.20BLT remain stable(ΔC/C_25°C≤±15%)at the test temperature of-100℃ to 350℃,indicates that the addition of BLT plays an important role in stabilizing the dielectric constants of BSTZ.As x rises from x=0 to x=0.20,the band gap₂)of（1-x）BSTZ-x BLT enhances from 2.10 e V to 3.11 e V,which helped to enhance the insulation of the sample.In order to reduce the cost of raw materials in production,in this experiment,a series of（1-x）Ba_0.6Sr_0.4Ti_0.7Zr_0.3O₃-x Bi(Zn_0.5Zr_0.5)O₃（x=0.05,0.10,0.15）ceramics were prepared by adding the cheaper raw material Bi(Zn_0.5Zr_0.5)O₃（BZZ）to the Ba_0.6Sr_0.4Ti_0.7Zr_0.3O₃ matrix.The samples of 0.95BSTZ-0.05BZZ,0.90BSTZ-0.10BZZ and 0.85BSTZ-0.15BZZ were sintered at 1400℃、1340℃ and 1290℃ for 4 hours,respectively.The X-ray diffraction results showed that（1-x）Ba_0.6Sr_0.4Ti_0.7Zr_0.3O₃-x Bi(Zn_0.5Zr_0.5)O₃（x=0.05,0.10,0.15）have pseudo-cubic phase.The AGS of（1-x）BSTZ-x BZZ ranged from 2.17μm to 6.51μm,and there was no significant elemental aggregation in all groups of samples.Ferroelectric tests showed that the critical electric field corresponding to the saturation polarization intensity of 0.95BSTZ-0.05BZZ reach150 k V/cm,which upgraded 80 k V/cm than the sample of BSTZ.The permittivity of0.85BSTZ-0.15BZZ remains stable at the test temperature of-100℃ to 350℃(TCC_25°C≤±15%and TCC_150°C≤±15%).The UV-Vis tests show that the band width of（1-x）BSTZ-x BZZ ceramics is in the range of 2.84～3.10 e V.