• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.629-633
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• 2002

The degradation behaviour of ZPCCL-based varistor ceramics composed of 97.5 mol%ZnO-0.5 mol% $Pr_6O_{11}-1.0$ mol% $Cr_2O_3-0.5$ mol% $La_2O_3$ was investigated under various DC accelerated aging streses. The varistor ceramics sintered for 1 h exhibited excellent nonlinearity, in which the nonlinear exponent is 81.6 and the leakage current is $0.2{\mu}A$. It was found that this varistor ceramics possess high stability, in which the variation rates of varistor voltage, nonlinear exponent, and leakage current are -1.14%, -3.7%, and 85.0%, respectively, against DC accelerated aging stress. On the contrary, the varistor ceramics sintered for 2 h also exhibited high nonlinearity and stability, but they were bad characteristics, compared with the varistor ceramics sintered for 1 h.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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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, $0.95 V_{1mA}/150^{\circ}C/24h$.

• 한국전기전자재료학회논문지
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• 제15권10호
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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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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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.

• Transactions on Electrical and Electronic Materials
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• 제16권6호
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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.

• 한국재료학회지
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• 제16권7호
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• pp.416-421
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• 2006

The varistor properties of ZPCCL-based ceramics were investigated at different $La_2O_3$ contents in the range of $0{\sim}2.0$ mol%. As $La_2O_3$ content increased, the ceramic density greatly increased in the range of $4.71{\sim}5.77\;g/cm^3$ and the varistor voltage greatly decreased in the range of $503.5{\sim}9.4$ V. The varistor with 0.5 mol% $La_2O_3$ exhibited good nonlinearity, in which the nonlinear exponent is 81.6 and the leakage current is 0.2 ${\mu}A$. Furthermore, the varistors exhibited the high electrical stability, with $%{\Delta}V_{1mA}=-1.1%,%{\Delta}{\alpha}=-3.7%$, and $%{\Delta}I_L=+100%$ for DC accelerated aging stress condition of 0.95 $V_{1mA}/150^{\circ}C/24$ h.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.344-347
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• 2003

The varistor properties of the ZPCCT-based ceramics, which are composed of Zn-Pr-Co-Cr-Tb oxides, were investigated with $Tb_4O_7$ content in the range of $0.0{\sim}1.0\;mol%$. As $Tb_4O_7$ content is increased, the ZPCCT-based ceramics exhibited very high densification based on increasing density in the range of $5.73{\sim}5.84\;g/cm^3$. The varitor voltage($V_{1mA}$) and nonlinear exponent($\alpha$) was increased in the range of 280.9 to 751.8 and 29.8 to 44.4 with increasing $Tb_4O_7$ content, respectively. In particular, the maximum $\alpha$ of 44.4 was obtained from 1.0 mol% $Tb_4O_7$ and the, minimum leakage current($I_{\ell}$) of $1.0\;{\mu}A$ was obtained from 0.5 mol% $Tb_4O_7$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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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.

• Transactions on Electrical and Electronic Materials
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• 제15권4호
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• pp.213-216
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• 2014

The microstructure and varistor properties of ZPCCAE ($ZnO-Pr_6O_{11}-CoO-Cr_2O_3-Al_2O_3-Er_2O_3$) ceramics were investigated with different erbium amounts. Analysis of the microstructure indicated that the ceramics consisted of ZnO grains as a bulk phase, and intergranular layers (mixture of $Pr_6O_{11}$ and $Er_2O_3$) as a minor secondary phase. With the increase of the doped erbium amount, the densities of sintered pellets increased from 5.63 to $5.82g/cm^3$, and the average grain size decreased from 9.0 to $5.7{\mu}m$. The increase of the doped erbium amount increased the breakdown field from 2,649 to 5,074 V/cm, and the nonlinear coefficient from 27.6 to 39.1. It was found that in the range of 0.25 to 0.5 mol%, the doped erbium had little effect on the microstructure and electrical properties.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.489-494
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• 2001

In this thesis, the microstructure and electrical properties of ZnO varistors were investigated according to ZnO varistors with various formulation. A∼E's ZnO varistor ceramics were exhibited good density, 95% of theory density and low porosity, 5%, wholly. The average grain size of A-E's ZnO varistor ceramics exhibited 11.89$\mu\textrm{m}$, 13.57$\mu\textrm{m}$, 15.44$\mu\textrm{m}$, 11.92$\mu\textrm{m}$, 12.47$\mu\textrm{m}$, respectively. Grain size of C's ZnO varistor is larger and grain size of A and D's are smaller than other varistors. In the microstructure, A∼E's ZnO varistor ceramics sintered at l130$^{\circ}C$ was consisted of ZnO grain(ZnO), spinel phase(Zn$\sub$2.33/Sb$\sub$0.67/O$_4$), Bi-rich Phase(Bi$_2$O$_3$) and inergranular phase, wholly. Reference voltage of A∼E's ZnO varistor sintered at 1130$^{\circ}C$ decreased in order D, E > A > B > C's ZnO varistors. Nonlinear exponent of varistors exhibited high characteristics, above 30, wholly. Consequently, C's ZnO varistor exhibited good nonlinear exponent, 68. Lightning impulse residual voltage of A, B, C and E's ZnO varistors suited standard characteristics, below 12kV at current of 5kA.