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Citrate Method Preparation and Dielectric Properties of Ba0.95Ca0.05Zr0.2Ti0.8O3 Based Ceramics

Author: ShiZuo
Tutor: XuQing
School: Wuhan University of Technology
Course: Materials Science
Keywords: Citrate method synthesis Sinterability Microstructure Dielectric properties Energy storage density
CLC: TQ174.1
Type: Master's thesis
Year: 2011
Downloads: 125
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Abstract


Ba1-xZrxTiO3 based solid solutions have high dielectric constants, low dielectric losses and high insulation strength. These desired properties make them promising candidate materials for dielectric ceramic capacitors for energy storage usage. This dissertation focuses on preparation, structure and dielectric properties of Ba0.95Ca0.05Zr0.2Ti0.8O3 (BCZT) based dielectric ceramics. Superfine powders of the BCZT and MgO-CaO-Al2O3-SiO2 (MCAS) glass were synthesized by a citrate method. Ceramic specimens with the nominal composition of BCZT+x wt.%MCAS (x=0-8) were fabricated from the superfine powders. The role of the MACS glass component on sinterability, structure and dielectric properties of the composite specimens were investigated with respect to its content. Moreover, a preliminary research was conducted to examine the energy storage property of the ceramic specimens.The powders of the BCZT and MCAS have been derived from the citrate method. Chemical principles of synthesizing the MCAS glass powder by the citrate route have been investigated. It was found that the amount of citric acid employed in the synthetic system acted an important role in determining the morphology of the resulting MCAS glass powder. By modifying the synthetic conditions, superfine powders of the BCZT and MCAS were produced by the citrate method. The two powders had analogous particle sizes of about 80 nm.The sinterability of the ceramic specimens has been investigated in relation to the morphology of the powders and the content of the MACS component. The BCZT powder exhibited high sinterability and the ceramic specimen sintered at 1260℃attained a relative density of about 94%. By comparison, the composite specimens presented improved sinterability and relative densities exceeding 95% at sintering temperatures around 1140℃. All the ceramic specimens had a fine-grained (around 240 nm) microstructure, which is related to the superfine morphology of the BCZT powder.The effect of the MACS on the dielectric properties of the composite ceramics has been investigated. Compared with the BCZT ceramic specimen, the composite specimens with different MACS contents showed enhanced resistivity and reduced bias-field-dependence of dielectric properties. Meanwhile, the composite specimens displayed an improved thermal stability of the dielectric properties. Moreover, the addition of the MACS component into the BCZT led to an obviously dielectric relaxor behavior.The energy storage peculiarity of the ceramic specimens has been preliminarily inspected. At the bias field of 120 kV/cm, the composite ceramic of Ba0.95Ca0.05Zr0.2Ti0.8O3+3wt.% MCAS showed an energy storage density of 0.36J/cm3 and an energy storage efficiency of 74.3%.

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