• 한국전기전자재료학회논문지
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• 제32권3호
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• pp.241-245
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• 2019

This work presents the response characteristics of a ZnO varistor to conductive EMP. An E1 pulse, standardized to MIL-STD-188-125-1, was applied to the varistors wherein the residual current and response times were measured with the applied E1 pulse current. Additionally, the response time was measured according to the length of the connection path. Consequently, the amplitude of the residual voltage through the ZnO varistors was increased with increasing amplitude of the applied E1 pulse current. As the length of the connection path increased, the operating response time and residual peak voltage also increased. These results indicate that the response characteristics of ZnO varistors can be applied to basic data to support the use of varistors as a protective measure against conductive EMP.

• 한국전기전자재료학회논문지
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• 제32권4호
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• pp.276-280
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• 2019

In this study, we investigated the crystal defects and grain boundary properties in a ZZCCC ($ZnO-Zn_2BiVO_6-Co_3O_4-Cr_2O_3-CaCO_3$) varistor, with the liquid-phase sintering aid $Zn_2BiVO_6$ developed by our laboratory. The ZZCCC varistor sintered at $1,200^{\circ}C$ exhibited excellent nonlinear current-voltage characteristics (${\alpha}=63$), with oxygen vacancy ($V_o^*$ ; 0.35 eV) as a main defect, and an apparent activation energy of 1.1 eV with an electrically single grain boundary. Therefore, among the various additives to improve the electrical properties of ZnO varistors, if $Zn_2BiVO_6$ is used as a liquid phase sintering aid, it will be ideal to use Co for the oxygen vacancy and Ca for the electrically single grain boundary. This will allow the good properties of ZnO varistors to be maintained up to high sintering temperatures.

• 한국전기전자재료학회논문지
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• 제13권5호
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• pp.383-389
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• 2000

The relationship between the DC degradation characteristics of the ZnO varistor and the ambient sintering-process is investigated in this study. ZnO varistors made o matsuoka’s composition were fabricated by standard ceramic techniques. The ambient sintering-process is performed at the extraordinary electrical-furnace which is equipped with the vacuum system. Gases used in sintering process were oxygen nitrogen argon and air. Using XRD and SEM the phase and microstructure of samples were analyzed respectively. The conditions of DC degradation tests were conducted at 115$\pm$2$^{\circ}C$ for 13 h. Current-voltage analysis is used to determine nonlinear coefficients($\alpha$). Frequency analysis are performed to understand electrical properties as DC degradation test. From above analysis it is found that the ZnO varistor sintered in oxygen atmosphere showed superior properties at the DC degradation test and degradation phenomenon of ZnO varistor is caused by the change of electrical properties in grain boundary. These results are in accordance with Gupta’s degradation model.

• 한국전기전자재료학회논문지
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• 제23권11호
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• pp.875-879
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• 2010

In this study, we have characterized the roles of $Cr_2O_3$ on the sintering and electrical properties of ZnO. The densification and grain growth of Cr-doped ZnO (ZCr) system was mainly influenced by Cr contents. In the beginning of sintering, the densification of ZnO was retarded as reducing the Zni concentration in ZnO lattice with Cr doping. And the densification and grain growth of ZnO was more retarded due to a formation of spinel phase with increasing the Cr contents. ZCr system revealed varistor behavior with nonlinear coefficient $\alpha$ of 3~23 depending on the sintering temperature, implying double Schottky barrier formation on the grain boundary of ZnO. Especially the best varistor characteristics should be developed with 0.1~0.5 at% Cr contents and under $1100^{\circ}C$ in ZCr systems.

• Journal of Advanced Marine Engineering and Technology
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• 제23권2호
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• pp.150-158
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• 1999

The process of designing protective circuits against damage by transient overvoltages requires much work and expensive equipment. However computer simulation using PSpice can overcome these problems. In this paper a gas tube and a ZnO varistor Pspice-model considering the steepness of the wave-front were presented. The effects of various waveforms on the transient behaviors and firing volt-ages of a gas tube were modeled by controlled voltage source E controlled current source G and TABLE function of PSpice. And the nonlinear characteristics of a ZnO varistor were modeled by controlled voltage source E and H. To estimate the characteristics of the models proposed various waveforms specified in IEC Std. 1000310-4-5 were used in the simulation and the actual tests. The simulation results were compared with test results and showed good agreement.

• 한국전기전자재료학회논문지
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• 제18권12호
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• pp.1111-1116
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• 2005

ZnO varistor ceramics added a glass-frit 0.03 $wt\%$ were fabricated with variation of sintering temperature. The sintering temperature and time were $1125^{\circ}C\~1200^{\circ}C$ and 2 h. The average grain sizes increased and the varistor voltage decreased with increasing the sintering temperature. The values of the specimen sintered at $1200^{\circ}C$ were $23.7\;{\mu}m$ and 329 V, respectively. The leakage current of all specimens was less than $1\;{\mu}A$ at DC $82\%$ of varistor voltage. The clamping voltage ratio of the specimen sintered at $1175^{\circ}C$ was 1.37. The endurance of surge current and the deviation of varistor voltage of the specimen sintered at $1175^{\circ}C$ were 6400 $A/cm^2$ and ${\Delta}-2.81\%$, respectively. After the High Temperature Load Test(HTLT) at $85^{\circ}C$ for 1000 h, the specimen sintered at $1175^{\circ}C$ showed the lowest deviation of varistor voltage of ${\Delta}-1.92\%$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.307-308
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• 2005

ZnO varistor ceramics were fabricated as a function of the sintering temperature from $1125^{\circ}C$ to $1200^{\circ}C$ with glass-frit 0.03wt% addition. The average grain size was increased from 10.4 ${\mu}m$ to 23.7 ${\mu}m$, and varistor voltage was decreased from 538 V to 329 V with rising of the sintering temperature. The nonlinear coefficient a showed similar value from 75 to 80 and leakage current of all specimens exhibited the result of $1{\mu}A$ at 82% of varistor voltage. But the clamping voltage ratio of the specimens sintered at $1175^{\circ}C$ was 1.37 at 25A [$8/20{\mu}s$]. Also, endurance of surge current and deviation of varistor voltage of sintered specimens at $1175^{\circ}C$ were $6400A/cm^2$, $\Delta$-3.32%, respectively.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1985년도 하계학술회의논문집
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• pp.187-188
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• 1985

• 한국재료학회지
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• 제13권10호
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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$.

• 한국세라믹학회지
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• 제37권2호
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• pp.186-193
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• 2000

Effects of 1.0 mol% CoO addition on sintering and the electrical properties of ZnO-Bi2O3-Sb2O3(ZBS) varistor system with 3.0 mol% co-addition of Sb2O3 and Bi2O3 at various Sb/Bi ratio (0.5, 1.0, and 2.0) were investigated. Cobalt had little influence on the liquid-phase formation and the pyrochlore decomposition temepratures of ZBS, while densification was mainly dependent on Sb/Bi ratio: when Sb/Bi=0.5, excess Bi2O3 irrelevant to the formation of pyrochore(Zn2Sb3Bi3O14) forms eutectic liquid at ~75$0^{\circ}C$ which promotes densification and grain growth; with Sb/Bi=2.0, the second phase Zn7Sb2O12 formed by excess Sb2O3 irrelevant to the formation of the pyrochlore retards densification up to ~100$0^{\circ}C$. These phases caused the coarsening and uneven distribution of the second phase particles on the grain boundaries of ZnO above the pyrochlore decomposition temperature(~105$0^{\circ}C$), which led to broad size dist-ribution of ZnO; the specimen with Sb/Bi=1.0 showed homogeneous microstructure compared with the others, which enabled improved varistor characteristics. Doping of Co increased the nonlinearity and the potential barrier height of ZBS, which is thought to stem from improved sintering behavior such as homogenized microstructure due to size reduction and even distribution of the second phase and suppressed volatility of Bi2O3, as well as the improvement in the potential barrier structure via increased donor and interface electron trap densities.