Journal of the Korean Institute of Electrical and Electronic Material Engineers (한국전기전자재료학회논문지)

The Korean Institute of Electrical and Electronic Material Engineers (한국전기전자재료학회)
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Effects of CaCO3 on the Defects and Grain Boundary Properties of ZnO-Co3O4-Cr2O3-La2O3 Ceramics

ZnO-Co3O4-Cr2O3-La2O3 세라믹스의 결함과 입계 특성에 미치는 CaCO3의 영향

  • 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)
  • 홍연우 (한국세라믹기술원 전자소재부품센터) ;
  • 하만진 (한국세라믹기술원 전자소재부품센터) ;
  • 백종후 (한국세라믹기술원 전자소재부품센터) ;
  • 조정호 (한국세라믹기술원 전자소재부품센터) ;
  • 정영훈 (한국세라믹기술원 전자소재부품센터) ;
  • 윤지선 (한국세라믹기술원 전자소재부품센터)
  • Received : 2018.05.15
  • Accepted : 2018.05.28
  • Published : 2018.07.01
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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.

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