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http://dx.doi.org/10.4313/JKEM.2010.23.12.942

Sintering and Electrical Properties of Cr-doped ZnO-Bi2O3-Sb2O3  

Hong, Youn-Woo (Bio-IT Convergence Center, Korea Institute of Ceramic Engineering and Technology)
Shin, Hyo-Soon (Bio-IT Convergence Center, Korea Institute of Ceramic Engineering and Technology)
Yeo, Dong-Hun (Bio-IT Convergence Center, Korea Institute of Ceramic Engineering and Technology)
Kim, Jin-Ho (School of Materials Science and Engineering, Kyungpook National University)
Publication Information
Journal of the Korean Institute of Electrical and Electronic Material Engineers / v.23, no.12, 2010 , pp. 942-948 More about this Journal
Abstract
In this study we aims to examine the effects of 0.5 mol% $Cr_2O_3$ addition on the reaction, microstructure development, resultant electrical properties, and especially the bulk trap and interface state levels of ZnO-$Bi_2O_3-Sb_2O_3$ (Sb/Bi=0.5, 1.0, and 2.0) systems (ZBS). The samples were prepared by conventional ceramic process, and characterized by XRD, density, SEM, I-V, impedance and modulus spectroscopy (IS & MS) measurement. The sintering and electrical properties of Cr-doped ZBS (ZBSCr) systems were controlled by Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$) was decomposed more than $100^{\circ}C$ lowered on heating in ZBS (Sb/Bi=1.0) by Cr doping. The densification of ZBSCr (Sb/Bi=0.5) system was retarded to $800^{\circ}C$ by unknown Bi-rich phase produced at $700^{\circ}C$. Pyrochlore on cooling was reproduced in all systems. And $Zn_7Sb_2O_{12}$ spinel ($\alpha$-polymorph) and $\delta-Bi_2O_3$ phase were formed by Cr doping. In ZBSCr, the varistor characteristics were not improved drastically (non-linear coefficient $\alpha$ = 7~12) and independent on microstructure according to Sb/Bi ratio. Doping of $Cr_2O_3$ to ZBS seemed to form $Zn_i^{..}$(0.16 eV) and $V^{\bullet}_o$ (0.33 eV) as dominant defects. From IS & MS, especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one (1.1 eV) and electrically inactive intergranular one (0.95 eV) with temperature.
Keywords
ZnO varistor; $Cr_2O_3$; Sintering; Electrical properties; Impedance spectroscopy;
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