Microstructure and Crystal Phases of Praseodymium Oxides in Zinc Oxide Varistor Ceramics |
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Authors: | Yih-Shing Lee Kao-Shiang Liao Tseung-Yuen Tseng |
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Affiliation: | Department of Electronics Engineering and Institute of Electronics, National Chiao-Tung University, Hsinchu, Taiwan, Republic of China |
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Abstract: | The effect of sintering temperature on the microstructure and crystal phases of the intergranular praseodymium oxides in ZnO varistor ceramics was investigated using transmission electron microscopy and high-resolution electron microscopy. The ZnO grains were three-dimensionally separated from the intergranular praseodymium oxides. On the basis of microdiffraction analyses of the intergranular layer, the phase transformation from fcc-Pr6O11 into hcp-Pr2O3 was found when the sintering temperature increased from 1300° to 1350°C. The defect reaction equation and the decrease of donor concentration with increasing sintering temperature can verify the certainty of phase transition during the liquid-phase sintering observed by transmission elecron microscopy. Additionally, on the basis of the small variations of the breakdown voltage per grain boundary, the number of active grain boundaries is not a dominant factor for the donor concentration dependence on the sintering temperature. |
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