• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.10
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• pp.897-901
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• 2003

The microstructure and varistor characteristics of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Dy$_2$O$_3$(ZPCCD)-based ceramics were investigated with Dy$_2$O$_3$ content in the range of 0.0∼2.0 mol%. As Dy$_2$O$_3$ content is increased, the average grain size was decreased in the range of 18.6∼4.7 $\mu$m and the density was decreased in the range of 5.53∼4.34 g/cm$^3$. While, the varistor voltage was increased in the range of 39.4∼436.6 V/mm and the nonlinear exponent was in the range of 4.5-66.6 with increasing Dy$_2$O$_3$ content. The addition of Dy$_2$O$_3$ highly enhanced the nonlinear properties of varistors, compared with the ceramics without Dy$_2$O$_3$ Particularly, the ceramics with Dy$_2$O$_3$ content of 0.5 mol% exhibited the highest nonlinearity, in which the nonlinear exponent is 66.6 and the leakage current is 1.2 $\mu$A.A.A.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1275-1281
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• 1997

ZnO varistors containing 5.0 at% Co3O4 and Pr6O11, ranging from 0.1 to 1.0 at%, were sintered at 130$0^{\circ}C$ and 135$0^{\circ}C$. The I-V characteristics and nonlinear coefficients of the specimens were investigated with respect to Pr addition and sintering temperature. In general the specimens sintered at 130$0^{\circ}C$ showed better varistor characteristic than those fired at 135$0^{\circ}C$, which seemed to be related with the liquid phase formation during sintering. The barrier heights obtained from C-V relations, 0.29-1.36 eV, were different from those acquired using resistivity-temperature plots measured at low voltage per grain boundary. Therefore the estimation of potential barrier heights using C-V relations is better suited for the specimens prepared in this study. The carrier densities obtained using C-V relations were ~1018 cm-3.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.1
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• pp.48-56
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• 1998

Pr\ulcornerO\ulcorner-based ZnO varistors were fabricated in the range of $Y_2$O$_3$additive content from 0.5 to 4.0mol%, and its microstructure and electrical properties were investigated. Yttrium was distributed nearly in the grain boundaries and the cluster phase formed at nodal point but more in cluster phase. The average grain size was decreased markedly from 34.9 to 8.6${\mu}{\textrm}{m}$ with increasing $Y_2$O$_3$additive content. It is believed that the decrease of grain size is attributed to the formation of cluster phase and the weakening of driving force for liquid sintering. As a result, $Y_2$O$_3$was acted as the inhibitor of the grain growth. With increasing $Y_2$O$_3$additive content, the varistor voltage, the activation energy, and the nonlinear exponent increased whereas the leakage current decreased, especially 4.0mol% $Y_2$O$_3$-added varistor exhibited very good I-V characteristics; nonlinear exponent 87.42 and leakage current 46.77nA. On the other hand, as $Y_2$O$_3$additive content increases, the varistor showed tendency of the salient decrease for donor concentration and the increase for barrier height. Conclusively, it is estimated that ZnO:Pr varistor compositions added more than 2.0mol% $Y_2$O$_3$are to be used to fabricate useful varistors.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.9
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• pp.924-929
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• 2004

The microstructure, electrical and dielectric characteristics of $ZnO-{Pr}_6{O}_11-{CoO}-{Dy}_2{O}_3$-based varistors were investigated without and with various metal oxide additives(NiO, MgO, Cr$_2$O$_3$). The average grain size decreased in the range of 18.4 $\backsim$ 11.5 $\mu$m, in order of NiO\longrightarrowMgO\longrightarrow{Cr}_2{O}_3$ and the density decreased in the range of 5.62 \backsim 5.33 $g/{cm}^3$ in order of NiO\longrightarrowCr$_2$O$_3$\longrightarrowMgO. While, the nonlinear exponent increased In the range of 19.8$\backsim$67.4 in order of NiO\longrightarrowMgO\longrightarrow${Cr}_2{O}_3$ and the leakage current decreased in the range of 25.6 $\backsim$ 1.2 $\mu$A in order of NiO\longrightarrow${Cr}_2{O}_3$\longrightarrowMgO. Among all varistors, the Cr$_2$O$_3$-added varistor exhibited the highest nonlinearity, with a nonlinear exponent of 67.4 and a leakage current of 1.2 $\mu$A. Furthermore, this varistor exhibited the lowest dielectric dissipation factor of 0.0407.

• Transactions on Electrical and Electronic Materials
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• v.7 no.4
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• pp.189-195
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• 2006

The microstructure, electrical and dielectric properties, and stability against DC accelerated aging stress of the varistors, which are composed of quaternary system $ZnO-Pr_6O_{11}CoO-Cr_2O_3-based$ ceramics, were investigated for different $La_2O_3$ contents. The increase of $La_2O_3$ content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0mol%. The highest nonlinearity was obtained from 0.5mol% $La_2O_3$, with the nonlinear coefficient of 81.6 and the leakage current of $0.1{\mu}A$. The varistors doped with 0.5mol% $La_2O_3$ exhibited high stability, in which the variation rates of breakdown voltage, nonlinear coefficient, leakage current, dielectric constant, and dissipation factor were -1.1%, -3.7%, +100%, +1.4%, and +8.2%, respectively, for stressing state of $0.95V_{1mA}/150^{\circ}C/24h$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.8
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• pp.664-670
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• 2002

The electrical characteristics of $ZnO-Pr_6O_{11}-CoO-Cr_2O_3-Y_2O_3$(ZPCCY)-based varistors were investigated with $Y_2O_3$ content in the range of 0.0~4.0 mol%. As $Y_2O_3$ content is increased, the average grain size was markedly decreased in the range of 18.6~3.2 $\mu m$ and the density of the ceramic was decreased in the range of 5.53 ~3.74 $g/\textrm{cm}^3$. While, the varistor voltage was increased in the range of 39.4~748.1 V/mm and the nonlinear exponent was in the range of 4.5~51.2 with increasing $Y_2O_3$ content. The addition of $Y_2O_3$ greatly enhanced the nonlinear properties of varistors, compared with the varistor without $Y_2O_3$. In particular, the varistors with $Y_2O_3$content of 0.5 mol% exhibited the highest nonlinearity, in which the nonlinear exponent is 51.2 and the leakage current is 1.3 $\mu A$. The donor concentration and the density of interface states were decreased in the range of (4.19~0.14) $\times$10$^{18}$ /㎤ and (5.38~1.15)${\times}10^{18}/\textrm{cm}^3$, respectively, with increasing $Y_2O_3$ content.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.242-245
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• 2000

The electrical properties of ZPCCE (ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Er$_2$O$_3$) based varistors were investigated with sintering temperature in range of 1335 to 135$0^{\circ}C$ for 1h. As the sintering temperature increases, the nonlinear exponent decreased, but was high beyond 40 except for 1.0 mol% Er$_2$O$_3$. Among all ZPCCE varistors, the varistor having the highest nonlinear exponent was obtained by sintering at 1335$^{\circ}C$, containing 2.0 mol% Er$_2$O$_3$ and then the nonlinear exponent was 78.05, and the varistors with 0.5 mol% Er$_2$O$_3$ exhibited the lowest leakage current of 1.92 $\mu$A.A.A.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.3
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• pp.244-252
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• 2002

The electrical and dielectric behavior fort DC accelerated aging stress of P $r_{6}$ $O_{11}$-based Zno varistors cnsisting of ZnO-P $r_{6}$ $O_{11}$-CoO-C $r_2$ $O_3$-E $r_2$ $O_3$ were investigated with sintering temperature in the range of 1325~1345$^{\circ}C$. The varistor ceramics with increasing sintering temperature were more densified. A more densified varistors leaded to high stability for DC accelerated aging stress. Furthermore, the stability for DC accelerated aging stress was increased with the leakage current and dtan $\delta$/dV decreasing in order of 1325longrightarrow1335longrightarrow1345longrightarrow134$0^{\circ}C$ in sintering temperature. It was found that the stability for DC stress is affected more greatly by the leakage current and dtan $\delta$/dV than the densification. It is considered that the stability of varistors for DC stress can be estimated by considering the factors, such as the densification, leakage current, and dtan $\delta$/dV. As a result, the varistor sintered at 134$0^{\circ}C$ exhibited the highest stability, with %$\Delta$ $V_{lmA}$=-1.54%, %$\Delta$$\alpha$=-2.49%, %$\Delta$ $I_{\ell}$=+240.68%, 5%$\Delta$tan$\delta$=+29.96%.96%.96%.%.

• Journal of the Korean Ceramic Society
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• v.47 no.3
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• pp.249-255
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• 2010

To investigate optical properties of (V, Pr)-doped $ZrSiO_4$ green pigments, samples were prepared by the ceramic method using NaF and NaCl as mineralizers. They were characterized by X-ray diffraction, UV-Vis spectroscopy and Raman spectroscopy. The changes of color in the samples during heating and effect of mineralizers were studied in terms of valence of the vanadium and praseodymium in the zircon matrix. (V, Pr)-doped $ZrSiO_4$ pigments give rise to green coloration in $800^{\circ}C$. The oxidation state of V and Pr ions of pigments in the glazed samples were confirmed by UV-Vis absorption spectra. This absorption spectra showed three typical bands of trivalent Pr at the 445, 480~490, 592 nm due to f-f transitions and two broad bands of 302~380, 400~500 nm due to f-d transitions of tetravalent Pr. According to the increasing amounts of $Pr_6O_{11}$, the two broad bands showed decreasing intensity at 290, 640 nm due to d-d transitions of tetravalent V.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.410-414
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• 2001

The microstructure, V-I characteristics, and stability of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Y$_2$O$_3$based vairstors were investigated with cooling rate in the range of 2~8$^{\circ}C$/min. The cooling rate relatively weakly affected the microstructure, and the varistor voltage and the leakage current in the V-I chracteristics. But the nonlinear exponent relatively strongly affected by cooling rate. And the cooling rate also greatly affected the stability for DC stress. In gross, the varistors cooled with 4$^{\circ}C$/min exhibited the highest performance in the densification, nonlinearity, and stability. Especially, they exhibited a high stability, in which the variation rate of the varistor voltage and the nonlinear exponent is -1.44% and -4.85%, respectively, under more severe DC stress such as (0.80 V$_{1mA}$9$0^{\circ}C$/12 h)+(0.85 V$_{1mA}$115$^{\circ}C$/12 h)\`(0.90 V$_{1mA}$12$0^{\circ}C$/12 h)+(0.95 V$_{1mA}$1$25^{\circ}C$/12 h)+(0.95 V$_{1mA}$15$0^{\circ}C$/12 h). It should be emphasized that the stability of these varistors is much superior to that of others.s.of others.s.