• Transactions on Electrical and Electronic Materials
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• v.14 no.4
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• pp.193-198
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• 2013

The effects of additives (Cr, Nb, Dy, and Bi) on microstructure, electrical properties, dielectric characteristics, and aging behavior of $ZnO-V_2O_5-MnO_2-Co_3O_4-La_2O_3$ (ZVMCL) ceramics were systematically investigated. The phase formed in common for all ZVMCL ceramics modified with various additives consisted of ZnO grain as a main phase, and $Zn_3(VO_4)_2$ and $ZnV_2O_4$ as the secondary phases. The sintered density and average grain size were in the range of $5.4-5.54g/cm^3$ and $3.7-5.1{\mu}m$, respectively. The ZVMCL ceramics modified with Cr exhibited the highest breakdown field (6,386 V/cm) and the ZVMCL ceramics modified with Nb exhibited the lowest breakdown field (3,517 V/cm). All additives enhanced the nonlinear coefficient (${\alpha}$), by a small or large margin, in particular, additives such as Bi and Nb noticeably increased the nonlinear coefficient, with ${\alpha}=25.5$ and ${\alpha}=23$, respectively. However, on the whole, all additives did not improve the stability against a DC stress, compared with ZVMCL ceramics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.5
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• pp.402-410
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• 2000

The electrical properties and stability of Pr$_{6}$/O$_{11}$-based ZnO wvaristors consisting of ZnO-Pr$_{6}$/O$_{11}$-CoO-Dy$_{2}$/O$_{3}$ based ceramics were investigated in the Dy$_{2}$/O$_{3}$ additive content range o 0.0 to 2.0 mol%. The density was nearly constant 5.62 g/cm$^3$corresponding to 97% of theoretical density as Dy$_{2}$/O$_{3}$ additive content increases up to 0.5 mol%. However the density decreased as Dy$_{2}$/O sub 3/ additive content is further additive content. Pr$_{6}$/O$_{11}$-based ZnO varistors doped with 0.5mol% Dy$_{2}$/O$_{3}$ exhibited a good nonlinearity, which is 37.76 in the nonlinear exponent and 5.36 $mutextrm{A}$ in the leakage current. And they exhibited very stress (0.80 V$_{1mA}$/9$0^{\circ}C$/12h)+(0.85 V$_{1mA}$/115$^{\circ}C$/12h)+(0.95 V$_{1mA}$/1$25^{\circ}C$/12h). Consequently it was estimated that ZnO-0.5 mol% Pr$_{6}$/O$_{11}$-1.0 mol% CoO-0.5 mol% Dy$_{2}$/O$_{3}$ based ceramics will be sufficiently used as a basic composition to develop the advanced Pr$_{6}$/O$_{11}$-based ZnO varistors in the future.he future.uture.he future.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.1
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• pp.39-45
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• 2003

The varistor properties of ZnO-Pr$_{6}$O$_{11}$-CoO-based ceramics doped with Sm$_2$O$_3$were investigated in the addition range of 0.0~2.0 mol% Sm$_2$O$_3$at sintering temperature of 130$0^{\circ}C$ and 135$0^{\circ}C$. As Sm$_2$O$_3$ content is increased, the breakdown voltage was increased in the range of 348.9~521.8 V/mm for ceramics sintered at 130$0^{\circ}C$ and 8.5~381.3 V/mm for ceramics sintered at 135$0^{\circ}C$. On the whole, the increase of sintering temperature led to the low nonlinearity regardless of Sm$_2$O$_3$content. ZnO-Pr$_{6}$O$_{11}$-CoO-based ceramics doped with 1.0 mol% at each sintering temperature exhibited the most superior varistor properties, with the nonlinear exponent of 42.1 at 130$0^{\circ}C$, 36.8 at 135$0^{\circ}C$ and the leakage current of 9.2 $\mu$A at 130$0^{\circ}C$, 11.7 $\mu$A at 135$0^{\circ}C$.EX>.EX>.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.190-195
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• 2000

The electrical properties and stability of ZPCE varistors consisted of $ZnO-Pr_6O_{11}-CoO-Er_2O_3$ ceramics were investigated. $ZnO-Pr_6O_{11}-CoO-Er_2O_3$ based ceramics were sintered at $1300^{\circ}C$ and $1350^{\circ}C$, respectively, without and with 0.5 mol% $Er_2O_3$. The varistors sintered at $1300^{\circ}C$ exhibited a better nonlinearity than that $1350^{\circ}C$. The varistors with $Er_2O_3$ of 0.5 mol% exhibited a high nonlinear exponent of 52.8. However, they easily degraded due to the low density below 85% of TD. On the other hand, the varistors sintered at $1350^{\circ}C$ without $Er_2O_3$ exhibited an extremely poor nonlinearity, but the varistors with $Er_2O_3$ of 0.5 mol% exhibited a relatively good nonlinearity, which the nonlinear exponent is 34.8 and the leakage current is $7.4\;{\mu}A$ Morever, they exhibited a very high stability, which the variation rate of varistor voltage, nonlinear exponent, and leakage current are -0.9%, -2.9%, and +2.7%, respectively, under the third stress $(0.80 V_{1mA}/90^{\circ}C/12h)$ + $(0.85 V_{1mA}/115^{\circ}C/12h)$ + $(0.90 V_{1mA}/120^{\circ}C/12h)$. Consequently, it was estimated that $ZnO-Pr_6O_{11}-CoO-Er_2O_3$ ceramics will be usefully applied to develop the advanced $Pr_6O_{11}$-based ZnO varistors.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.330-333
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• 2002

The stability against DC accelerated aging stress of $Dy_{2}O_{3}-doped$ $ZnO-Pr_{6}O_{11}-based$ varistor ceramics was investigated. The calculated nonlinear exponent$(\alpha)$ in varistor ceramics without $Dy_{2}O_{3}$ was only 4.9, whereas the $\alpha$ value of the varistors with $Dy_{2}O_{3}$ was abruptly increased in the range of 48.8 to 58.6. The varistor ceramics with $Dy_{2}O_{3}$ content of 1.0 mol% exhibited maximum ${\alpha}$, reaching 58.6, whereas they exhibited very poor stability. While, The varistor ceramics doped with 0.5 mol% $Dy_{2}O_{3}$ exhibited not only the high nonlinearity, which the ${\alpha}$ is 55.3 and the leakage current is $0.1{\mu}A$， but also the highest stability, which the variation rates of varistor voltage and nonlinear exponent are -0.8% and -14.3%, respectively, under DC accelerated aging stress, $0.95 V_{1mA}/150^{\circ}C/24h$.

• Transactions on Electrical and Electronic Materials
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• v.16 no.6
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• pp.308-311
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• 2015

V₂O₅/Mn₃O₄/Nb₂O₅ codoped zinc oxide varistor ceramics were sintered at a temperature range as low as 875~950℃. The voltage clamping characteristics of V₂O₅/Mn₃O₄/Nb₂O₅ codoped zinc oxide varistor ceramics were investigated at a pulse current range of 1~50 A. The sintering temperature had a significant effect on clamp voltage ratio, which exhibits surge protection capabilities. The varistor ceramics sintered at 875℃ exhibited the best clamping characteristics, in which the clamp voltage ratio was 2.69 at a pulse current of 50 A. The varistor ceramics sintered at 900℃ exhibited the highest electrical stability, where = 3,824 V/cm (initial 3,909 V/cm), and E_{1 mA/cm²} = 27 (initial 39) after application of a pulse current of 100 A.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.625-628
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• 2002

The electrical properties of the praseodymium-based ZnO varistor ceramics, which are composed of Zn-Pr-Co-Cr-Dy oxides were investigated with $Dy_2O_3$ amount. The average grain size of varistor ceramics was greatly decreased from 18.2 to 4.6 pm with increasing $Dy_2O_3$ amount. The calculated nonlinear exponent$({\alpha})$ in varistor ceramics without $DY_2O_3$ was only 4.9, whereas the a value of the varistors with $DY_2O_3$ was abruptly increased in the range of 48.8 to 58.6. In particular, the maximum value of a was obtained by doping of 1.0 mol% $DY_2O_3$, reaching 58.6. The measured leakage current$(I_l)$ value in varistors without $DY_2O_3$ was $85.45{\mu}A$, whereas the $I_{\ell}$ value of the varistors with $DY_2O_3$ was very abruptly decreased in the range of 1.10 to $0.12{\mu}A$. In particular, the minimum value of $I_{\ell}$ was obtained by doping of 0.5 mol% $DY_2O_3$, reaching $0.12{\mu}A$. The tan $\delta$ varied in V-shape, with minimum 2.28% at 0.5 mol% $DY_2O_3$. The donor concentration and the density of interface states were decreased in the range of $(4.66{\sim}0.25){\times}10^{18}cm^3$ and $(5.70{\sim}1.39){\times}10^{12}/cm^2$, respectively, as $DY_2O_3$ amount is increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05b
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• pp.179-184
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• 2000

The I-V characteristics of $ZnO-Pr_6O_{11}-CoO-Dy_2O_3$ based varistors were investigated in the $Pr_6O_{11}/CoO$ composition ratio range of 0.5/0.5 to 1.0/1.0 and sintering temperature range of 1300 to $1350^{\circ}C$ as the basic study to develop the advanced $Pr_6O_{11}$-based ZnO varistors. All varistors except for $Pr_6O_{11}$/CoO = 0.5/1.0 exhibited the best I-V characteristics at $1350^{\circ}C$. However, the varistors with $Pr_6O_{11}$/CoO= 0.5/1.0 exhibited the best I-V characteristics at $1350^{\circ}C$. The varistors with $Pr_6O_{11}$/CoO= 0.5/1.0 of all varistors exhibited the best I-V characteristics, which the nonlinear exponent is 36.9 and the leakage current is 7.6 ${\mu}A$ Therefore, it was estimated that ZnO-$Pr_6O_{11}-CoO-Dy_2O_3$ ceramics with $Pr_6O_{11}$/CoO= 0.5/1.0 will be usefully used as varistor materials in the future.

• Transactions on Electrical and Electronic Materials
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• v.13 no.5
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• pp.262-265
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• 2012

The Microstructure and nonlinear electrical properties of the ZPCCYT (ZnO-$Pr_6O_{11}$-CoO-$Cr_2O_3$-$Y_2O_3$-$Tb_4O_7$) varistors were investigated for different amounts of $Tb_4O_7$. The addition of $Tb_4O_7$ has a significant effect on microstructure and electrical properties. Analysis of the microstructure indicated that the ceramics consisted of ZnO grain as a main phase and a few secondary phases as a mix of $Pr_6O_{11}$, $Y_2O_3$, and $Tb_4O_7$. As the amount of $Tb_4O_7$ increased, the sintered densities of pellets increased from $\rho$ = 5.70 to $5.78g/cm^3$ and the average grain size decreased from d = 4.8 to $3.6{\mu}m$. The increase in the amount of $Tb_4O_7$ increased from $E_B$ = 7,473 to 10,035 V/cm and from ${\alpha}$ = 39.7 to 52.2. In particular, it was found that the ceramics modified with 1.0 mol% in the amount of $Tb_4O_7$ are suited for the varistors for high voltage in the light of a high sintered density and a high voltage gradient.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.467-471
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• 2001

DC accelerated aging characteristics of $Pr_{6}O_{11}$-based ZnO varistors, which are composed of $ZnO+Pr_{6}O_{11}+CoO+Cr_{2}O_{3}+Dy_{2}O_{3}$ ceramics were investigated with CoO content in the range of 0.5 - 5.0 mol%. The varistors doped with 1.0 mol% revealing maximum value(66.61) in the nonlinear exponent exhibited excellent stability, in which the variation rates of the varistor voltage, the nonlinear exponent and leakage current are -1.93%, -10.48%, and +288.79%, respectively, under DC accelerated aging stress, such as $(0.85V_{lmA}/115^{\circ}C/24h)+(0.90V_{lmA}120^{\circ}C/24h)+(0.95V_{lmA}/125^{\circ}C/24h)+(0.95V_{lmA}/150^{\circ}C/24h)$. Next the varistors doped with 2.0 mol% exhibiting the nonlinear exponent of 47.39 showed high stability.