• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.10
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• pp.876-882
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• 2002

The microstructure and electrical characteristics of ZPCD (ZnO-$Pr_{6}O_{11}$-CoO-$Dy_2O_3$) -based varistor ceramics were investigated with various $Pr_{6}O_{11}$/CoO ratios and sintering temperatures. The density of varistor ceramics with $Pr_{6}O_{11}$=1.0 was almost constant with sintering temperature, whereas it was increased noticeably in $Pr_{6}O_{11}$=0.5. Increasing $Pr_{6}O_{11}$ content enhanced the densification for any CoO content and the density was greatly affected not by CoO content but by $Pr_{6}O_{11}$ content. The varistor ceramics with $Pr_{6}O_{11}$/CoO=0.5/l.0 exhibited a higher nonlinearity than any other composition ratios. In particular, the varistor ceramics sintered at $1350^{\circ}C$ exhibited the best electrical properties, with nonlinear exponent of 37.8, leakage current of 7.6 ${\mu}$A, and tan $\delta$ of 0.059.

• 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, $0.95 V_{1mA}/150^{\circ}C/24h$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.308-311
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• 1999

The varistor characteristics of $ZnO-Pr_6O_11-CoO-Er_2O_3$-based ceramics were investigated. $ZnO-Pr_6O_11-CoO-Er_2O_3$-based ceramics were sintered at $1300^{\circ}C$ and $1350^{\circ}C$in the addition range 0.0~2.0mol% $Er_2O_3$, respectively. $ZnO-Pr_6O_11-CoO-Er_2O_3$-based ceramics, which are added with 0.5mol% $Er_2O_3$ at $1300^{\circ}C$ and l.Omol% $Er_2O_3$ at $1350^{\circ}C$ sintering temperature, exhibited the bestexcellent varistor characteristics, namely, the nonlinear exponent was better 52.78 at $1300^{\circ}C$ thanat 13$1350^{\circ}C$ and the leakage current was better 6.57$\mu\textrm$A at $1350^{\circ}C$ than at $1300^{\circ}C$. Consequently, it is estimated that $ZnO-Pr_6O_11-CoO-Er_2O_3$-based ceramics, which $Er_2O_3$ is added in the range 0.5~l.Omol% will begin to be used as a predominant basic composition of $PR_6O_11$-based ZnO varistors.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.705-709
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• 2003

The microstructure and electrical properties of the $Pr_6O_{11}$-based ZnO varistor ceramics, which are composed of Zn-Pr-Co-Cr-Tb oxides, were investigated with $Tb_4O_7$ amount. The varistor ceramics exhibited very high densification based on increasing density in the range of $5.73{\sim}5.85g/cm^3$ as $Tb_4O_7$ amount is increased. The calculated nonlinear exponent( ${\alpha}$ ) in varistor ceramics without $Tb_4O_7$ was only 8.9, whereas the ${\alpha}$ value of the varistor ceramics with $Tb_4O_7$ was abruptly increased in the range of 18.6 to 42.0. In particular, the maximum value(42.0) of ${\alpha}$ was obtained by doping of 1.0 mol% $Tb_4O_7$. The measured leakage current($I_{\ell}$) in varistor ceramics without $Tb_4O_7$ was $40.1{\mu}A$, whereas the $I{\ell}$ value of the varistors with $Tb_4O_7$ was very abruptly decreased below $5{\mu}A$. It is estimated that $Tb_4O_7$ additives will is applied usefully in development of varistors possessing high performance.

• Korean Journal of Materials Research
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• v.13 no.10
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• pp.645-650
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• 2003

The microstructure and electrical characteristics of $Pr_{6}$ $O_{11}$ -based ZnO varistor ceramics composed of $ZnO-Pr_{6}$ $O_{ 11}$/$-CoO-Cr_2$$O_3$-$Dy_2$$O_3$-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 was increased, the average grain size was decreased in the range of 18.6∼4.7 $\mu\textrm{m}$ and the density of the ceramic was decreased in the range of 5.53∼4.34 g/㎤. 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 varistor without $Dy_2$$O_3$. In particular, the varistor with $Dy_2$$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 $\mu\textrm{A}$. The donor concentration and the density of interface states were decreased in the range of $(4.19∼0.33) ${\times}$10^{18}$ //㎤ and $(5.38∼1.74) ${\times}$10^{12}$ $\textrm{cm}^2$, respectively, with increasing $Dy_2$$O_3$content. The minimum dissipation factor of 0.0302 was obtained from 0.5mol% $Dy_2$$O_3$.

• 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.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.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1631-1633
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• 2004

The surge current characteristics of ZnO-$Pr_6O_{11}$-CoO-$Cr_2O_3-Dy_2O_3$-based varistors were investigated with various $Dy_2O_3$ contents. The sintered density decreased in the range of $5.2{\sim}4.6g/cm^3$ with increasing $Dy_2O_3$ content. The incorporation of $Dy_2O_3$ markedly enhanced the nonlinear properties of varistors above 10 times in nonlinear exponent, compared with the varistor without $Dy_2O_3$. The varistor ceramics doped with 0.5 mol% $Dy_2O_3$ exhibited the highest electrical stability. However, the remainder varistors resulted in thermal runaway due to low density of varistor ceramics. The clamping voltage ratio exhibited a minimum value of 2.03 in 1.0 mol% $Dy_2O_3$ at surge current of 100 A(8/20 ${\mu}s$).

• 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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• 2005.07a
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• pp.367-368
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• 2005

The microstructure and electrical properties of $Pr_6O_{11}$-based ZnO varistors consisting of Zn-Pr-Co-Cr-Tb oxides were investigated with $Tb_4O_7$ content in the range of 0.25~1.0 mol%. The varistor ceramics exhibited very high densification in the range of 5.74~5.83g/$cm^3$ with increasing $Tb_4O_7$ content. Furthermore, the incorporation of $Tb_4O_7$ in varistor ceramics $Tb_4O_7$greatly increased All of the characteristic parameters. As a result, It was found that $Tb_4O_7$-added varistors are good for high voltage field.