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http://dx.doi.org/10.4313/JKEM.2018.31.5.307

Effects of CaCO3 on the Defects and Grain Boundary Properties of ZnO-Co3O4-Cr2O3-La2O3 Ceramics  

Hong, Youn-Woo (Electronic Materials & Component Center, Korea Institute of Ceramic Engineering and Technology)
Ha, Man-Jin (Electronic Materials & Component Center, Korea Institute of Ceramic Engineering and Technology)
Paik, Jong-Hoo (Electronic Materials & Component Center, Korea Institute of Ceramic Engineering and Technology)
Cho, Jeong-Ho (Electronic Materials & Component Center, Korea Institute of Ceramic Engineering and Technology)
Jeong, Young-Hun (Electronic Materials & Component Center, Korea Institute of Ceramic Engineering and Technology)
Yun, Ji-Sun (Electronic Materials & Component Center, Korea Institute of Ceramic Engineering and Technology)
Publication Information
Journal of the Korean Institute of Electrical and Electronic Material Engineers / v.31, no.5, 2018 , pp. 307-312 More about this Journal
Abstract
Liquid phases in ZnO varistors cause more complex phase development and microstructure, which makes the control of electrical properties and reliability more difficult. Therefore, we have investigated 2 mol% $CaCO_3$ doped $ZnO-Co_3O_4-Cr_2O_3-La_2O_3$ (ZCCLCa) bulk ceramics as one of the compositions without liquid phase sintering additive. The results were as follows: when $CaCO_3$ is added to ZCCLCa ($644{\Omega}cm$) acting as a simple ohmic resistor, CaO does not form a secondary phase with ZnO but is mostly distributed in the grain boundary and has excellent varistor characteristics (high nonlinear coefficient ${\alpha}=78$, low leakage current of $0.06{\mu}A/cm^2$, and high insulation resistance of $1{\times}10^{11}{\Omega}cm$). The main defects $Zn_i^{{\cdot}{\cdot}}$ (AS: 0.16 eV, IS & MS: 0.20 eV) and $V_o^{\bullet}$ (AS: 0.29 eV, IS & MS: 0.37 eV) were found, and the grain boundaries had 1.1 eV with electrically single grain boundary. The resistance of each defect and grain boundary decreases exponentially with increasing the measurement temperature. However, the capacitance (0.2 nF) of the grain boundary was ~1/10 lower than that of the two defects (~3.8 nF, ~2.2 nF) and showed a tendency to decrease as the measurement temperature increased. Therefore, ZCCLCa varistors have high sintering temperature of $1,200^{\circ}C$ due to lack of liquid phase additives, but excellent varistor characteristics are exhibited, which means ZCCLCa is a good candidate for realizing chip type or disc type commercial varistor products with excellent performance.
Keywords
ZnO varistor; $CaCO_3$; Defects; Grain boundary; Impedance spectroscopy;
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Times Cited By KSCI : 2  (Citation Analysis)
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