Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Effect of Sb/Bi Ratio on Sintering and Grain Boundary Properties of ZnO-Bi2O3-Sb2O3-NiO-Cr2O3 Varistor

Sb/Bi비가 ZnO-Bi2O3-Sb2O3-NiO-Cr2O3 바리스터의 소결과 입계 특성에 미치는 영향

  • 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 : 2012.12.03
  • Published : 2012.12.27
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Abstract

We have examined the co-doping effects of 1/2 mol% NiO and 1/4 mol% $Cr_2O_3$ (Ni: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 Ni,Cr-doped ZBS, ZBS(NiCr) 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 detected for all of compositions. For the sample with Sb/Bi = 1.0, the Pyrochlore was decomposed and promoted densification at lower temperature by Ni rather than by Cr. A homogeneous microstructure was obtained for all of the samples affected by ${\alpha}$-spinel. The varistor characteristics were not dramatically improved (non-linear coefficient, ${\alpha}$ = 5~24), and seemed to form ${Zn_i}^{{\cdot}{\cdot}}$(0.17 eV) and ${V_o}^{\cdot}$(0.33 eV) as dominant defects. From impedance and modulus spectroscopy, the grain boundaries were found to have been divided into two types, i.e., one is tentatively assigned to ZnO/$Bi_2O_3$ (Ni,Cr)/ZnO (0.98 eV) and the other is assigned to a ZnO/ZnO (~1.5 eV) homojunction.

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References

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