Abstract
The ZnO doped with Al 2O 3 showed the minimum electrical resistivity at an Al 2O 3 content of 0.25%. It was found that the ZnO doped with Al 2O 3 exhibited the resistance-temperature characteristic reversion from negative temperature coefficient of electrical resistivity (NTCR) to positive temperature coefficient of electrical resistivity (PTCR) at temperatures of about 450 and 250 °C for ceramics sintered at 1400 and 1300 °C, respectively. Both NTCR and PTCR features were weakened for samples with lower Al 2O 3 content or sintered at a higher temperature. Microstructure studies exposed that the densification process was significantly depressed when the Al 2O 3 addition levels were over about 1%.
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