Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Sintering and Electrical Properties According to Sb/Bi Ratio(II) : ZnO-Bi2O3-Sb2O3-Co3O4-Cr2O3 Varistor

Sb/Bi비에 따른 5원계 바리스터의 소결거동 및 전기적 특성(II) : ZnO-Bi2O3-Sb2O3-Co3O4-Cr2O3

  • Hong, Youn-Woo (Electronic Materials Convergence Division, KICET) ;
  • Lee, Young-Jin (Electronic Materials Convergence Division, KICET) ;
  • Kim, Sei-Ki (Electronic Materials Convergence Division, KICET) ;
  • Kim, Jin-Ho (School of Materials Science and Engineering, Kyungpook National University)
  • 홍연우 (한국세라믹기술원 전자소재융합본부) ;
  • 이영진 (한국세라믹기술원 전자소재융합본부) ;
  • 김세기 (한국세라믹기술원 전자소재융합본부) ;
  • 김진호 (경북대학교 신소재공학부)
  • Received : 2012.10.26
  • Accepted : 2012.12.10
  • Published : 2012.12.27
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Abstract

In this study we aimed to examine the co-doping effects of 1/6 mol% $Co_3O_4$ and 1/4 mol% $Cr_2O_3$ (Co:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and the grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Co,Cr-doped ZBS, ZBS(CoCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ were formed in all systems. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi = 1.0 by Cr rather than Co. A more homogeneous microstructure was obtained in all systems affected by ${\alpha}$-spinel. In ZBS(CoCr), the varistor characteristics were improved (non-linear coefficient, ${\alpha}$ = 20~63), and seemed to form ${Zn_i}^{{\cdot}{\cdot}}$(0.20 eV) and ${V_o}^{\cdot}$(0.33 eV) as dominant defects. From impedance and modulus spectroscopy, the grain boundaries were found to be composed of an electrically single barrier (0.94~1.1 eV) that is, however, somewhat sensitive to ambient oxygen with temperature. The phase development, densification, and microstructure were controlled by Cr rather than by Co but the electrical and grain boundary properties were controlled by Co rather than by Cr.

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