| With the development of surface mounted technology (SMT), the PTCR thermistor becomes miniaturization and integration. In order to meet the requirement of reduction-reoxidation process for multilayer chip PTCR thermistor, this paper have studied the effects of sintering temperature in reducing atmosphere, reoxidation temperature, Y-doped concentration and Ba/Ti ratio on the properties of PTCR thermistor materials.The BaTiO3 powder was prepared by solid phase method, and the green tape was prepared by organic tape casting technology. By changing the sintering temperature in reducing atmosphere and the reoxidation temperature, the effects on grain sizes, resistivities, PTC jumps and withstand voltages were studied. In the other hands, in order to obtain good performance of PTCR thermistor, the roles of Y-doped with different Ba/Ti ratios were investigated.The result reveals that the grain sizes increased with the increase of sintering temperature in reducing atmosphere, in the range from 1215℃to 1295℃. The effects of the same reoxidation condition could be weaker with higher sintering temperature. The resistivities of ceramic materials had a parabola relationship with reoxidation temperature, but the PTC jumps and the withstand voltages increased with the increase of reoxidation temperature. In addition, the resistivities of ceramic materials increased with the increase of Y-doped concentration, while the PTC jump decreased with it. The samples with Ba excess could obtain better performance than the samples with Ti excess in the process of reduction-reoxidation.Finally, the best sintering temperatures were set in the range from 1215℃to 1250℃, and the best reoxidation temperatures were set in the range from 800℃to 850℃. The sample with Ba/Ti=1.01 and 0.4mol% Y-doped, sintered at 1230℃in reducing atmosphere and reoxidation at 850℃, had the average grain size of 1.1μm, the resistivity of 256.7?·cm and the PTC jump of 218. |
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