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Research on Microstructure and Properties of ZnO Varistor Ceramics Induced by Laser Shock Processing

Author: JiGuang
Tutor: HuaYinQun
School: Jiangsu University
Course: Materials processing
Keywords: ZnO varistor ceramics laser shock wave nonlinear coefficient barrier height dielectric constant
CLC: TM282
Type: Master's thesis
Year: 2010
Downloads: 23
Quote: 0
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Abstract


Based on the phase transition of metal material induced by laser shock processing, In this paper, the experiment research was carried out on laser shock process experiment of ZnO varistor ceramics. ZnO varistor ceramics has been shocked processing by Nd-YAG laser. Electrical parameters of ZnO varistor ceramics were measured by CJ1001 Varistor Tester and morphology and microstructure of ZnO varistor ceramics was characterized by XRD and SEM. We made some mainly achievements as followed.The influence of sintering temperature on the electrical properties, density and microstructures of ZnO varistor ceramics were researched firstly. The results showed that the voltage gradient decreased, both nonlinear coefficient and density increased and then decreased, leakage current decreased and then increased with increasing sintering temperature. Meanwhile, When the sintering temperature gradually increased from 850℃to 1150℃, the phase transformation of Bi2O3 occured gradually:850℃was y-Bi2O3; 950℃was y-Bi2O3 andβ-Bi2O3; 1050℃wasβ-Bi2O3; 1150℃still was P-Bi2O3; when the sintering temperature at 1250℃, Bi2O3 disappeared, then worse electrical properties of ZnO varistor ceramics, the nonlinear coefficient was only 3.5; The change of Bi2O3 phase is an important reason for changing the electrical properties of ZnO varistor ceramics.And the experiment research on laser shock process experiment of ZnO varistor ceramics was carried out secondly. The effect of laser shock wave on the electrical properties of ZnO varistor ceramics was studied. A group of ZnO varistor ceramics were prepared in the methods of conventional fabrication process of electronic ceramics, gradually changed the sintering temperature to study changes in the electrical properties, the density and the microstructure of ZnO varistor ceramics. The results indicated that ZnO varistor ceramics in high-temperature sintering by laser shock processing, voltage gradient reduced by 15.6%; nonlinear coefficient substantially increased by 43.4%and leakage current reduced by 50%. The relative dielectric constant increased by 103%. Annealing treatment of ZnO varistor ceramics in high-temperature sintering by laser shock processes vs annealing treatment, the voltage gradient is essentially the same, nonlinear coefficient substantially increased by 31.6%and leakage current reduced by 33.3%. The relative dielectric constant increased by 68.9%. The microstructure of ZnO varistor ceramics by laser shock wave was analyzed by X-ray Diffraction(XRD), the results showed that phase transition of Bi2O3 happened, and generatedδ-Bi2O3, led increase in density of interface states and donor concentration, caused changes in electrical properties, especially the nonlinear coefficient is significantly increased. Meanwhile, the emergence of internal stress is due to Bi2O3 phase transition that caused the increase of dielectric constant.

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CLC: > Industrial Technology > Electrotechnical > Electrical materials > Electric and ceramic materials > Piezoelectric ceramics
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