• Journal of the Korean Ceramic Society
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• v.41 no.6
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• pp.464-470
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• 2004

The electrical stability of ZPCCY-based varistors composing of ZnO-Pr$_{6}$O$_{11}$-CoO-C $r_2$ $O_3$- $Y_2$ $O_3$ ceramics were investigated in various DC accelerated aging stress with sintering times. Sintering time greatly affected electrical properties and stability. Sintering time decreased nonlinear exponent in the range of 51.2∼23.8 and increased leakage current in the range of 1.3∼5.6 ${\mu}$A. The varistor sintered for 1 h exhibited high nonlinearity, whereas relatively low stability. On the contrary, the varistor sintered for 3 h exhibited low nonlinearity, whereas relatively high stability. But the varistor sintered for 2 h exhibited not only good nonlinearity, with nonlinear exponent of 38.6 and leakage current of 3.6 ${\mu}$A but also high stability, in which the variation rates of varistor voltage, nonlinear exponent, leakage current, and dissipation factor are -0.80%, -1.81 %, +74.4%, and +0.88%, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.1106-1110
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• 2003

The electrical characteristics of $A{\sim}C's$ ZnO varistors fabricated according to variable sintering condition, which sintering temperature is $l130^{\circ}C$ and speeds of pusher are A: 2mm/min, B: 4mm/min, C: 6 mm/min, respectively, were investigated. The varistor voltage of $A{\sim}C's$ ZnO varistors sintered at $1130^{\circ}C$ increased in order A < B $A{\sim}C's$ ZnO varistors exhibited below 2mA at rated voltage. Lightning impulse residual voltage of A's ZnO varistor suited standard characteristics, which is 3.85kV at 2.5kA, 4.4kV at 5kA and 5.16kV at 10kA. After multi lightning impulse residual voltage test of A's ZnO varistor exhibited good discharge characteristics which ZnO varistor reveals no evidence of puncture, flashover, cracking in visual examination. After high current impulse test of A's ZnO varistor exhibited good discharge characteristics, which variation rate of residual voltage is 0.4% before and after test, and revealed no evidence.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.3
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• pp.206-213
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• 2000

The microstructure and electrical properties of Pr$_{6}$/O sub 11/-Based ZnO varistors with Nd$_2$O$_3$ was doped in the range of 0.0 to 2.0 mol% were investigated. Most of the added Nd$_2$O$_3$were segregated at the nodal points and grain boundaries and were found to form the Nd-rich phase. In addition the bulk intergranular layer at the grain boundaries and nodal points was consisted of Nd-rich phase and Pr-rich phase. the average grain size was decreased in the range of 7.8 to 5.6${\mu}{\textrm}{m}$ with increasing Nd$_{2}$/O sub 3/ additive content. The nonlinearity of ZnO varistors sintered at 130$0^{\circ}C$ was much more excellent than that at 135$0^{\circ}C$ ZnO varistors doped with 1.0mol% Nd$_{2}$/O sub 3/ exhibited the best nonlinearity. which is 65.2 in the nonlinear exponent and 4.5$\mu$A in the leakage current. Consequently. it is estimated that Pr$_{6}$/O sub 11/ -based ZnO varistors doped with 1.0 mol% Nd$_{2}$/O sub 3/ are to be sufficiently used as basic composition to fabricate good varistors in the future.ure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.11
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• pp.969-974
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• 1998

The effects of $La_2O_3$on the microstructure and electrical characteristics of Pr-based ZnO varistors were investigated. The average grain size increased in the range of 21.9~56.3$\mu$ m with increasing $La_2O_3$additive content(0.0~2.0 mol%). La was, of course grain boundary, largely segregated at the nodal point. As $La_2O_3$additive content increases, threshold voltage and nonlinear coefficient decreased and leakage current increased. In particular, 2.0 mol% $La_2O_3$-added varistor exhibited low threshold voltage 17.0V/mm and nonlinear coefficient of about 6. Based on these results, this varistor can be said to be used as low-voltage varistor, if nonlinear coefficient is somewhat improved forward.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.281-285
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• 1998

The microstructure and conduction characteristics of ZnO varistor fabricated in the range of 0.0 ~ 4.0mol% $Y_20_3$ were investigated. With increasing$Y_20_3$ content, distribution of spinel phase decreased, whereas Y-rich phase segregated to the nodal point increased, as a result, the average grain size decreased in the range of $20.0 ~ 4.8{\mu}m$. $Y_20_3$ content showing relatively good conduction characteristics was l.Omol%, then nonlinear exponent and leakage current was 55.3, 0.66mA.respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.343-346
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• 1998

Degradation characteristics of the Pr-based ZnO varistor with $Y_2O_3$content (0.0-4.0 mol!%j were investigated. It was appeared that the variation of the J-E characteristics in the reverse direction before and after the applied stress with increasing $Y_2O_3$ content was larger than that of the forward direction but the variation was extrernly small. For all varistor, the leakage current with the stress time during the applied stress somewhat increased initialy but afterthat was almost constant or slightly decreased. The overall varistor voltage and nonlinear coefficient were less than 5%. Especially, in the case of Pr-based ZnO varistor containing 2.0 mol% to 4.0 mol% $Y_2O_3$, the variation of breakdown voltage and nonlinear coefficient was less than 1% and 5%. respectively. As a result, they showed good stability.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.10
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• pp.842-848
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• 1998

The stability of paraseodymium-based zinc oxide varistor consisting of Zn-Pr-Co-Cr-Y oxide was investigated according to yttria additives under different stress conditons, such as 0.8V\ulcorner\ulcorner/373K/12h and 0.85V\ulcorner\ulcorner/393K/12h. Wholly, all varistor after the stress showed nearly symmetric and stable I-V characteristics. Particularly, in the case of 2.0mol% and 4.0mol% yttria-added varistor showing a good I-V characteristics, the varation rate of varistor voltage were less 1% and that of nonlinear coefficient were about degree of 5%, and what is remarkable, leakage current with increasing stress time during the applied stress was almost constant. It the light of these facts, it is estimated that varistor constituents having 2.0mol% and 4.0mol% yittria, respectively, will be utilized to various application fields.

• 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 Ceramic Society
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• v.40 no.10
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• pp.943-948
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• 2003

The microstructure and electrical characteristics of Zn-Pr-Co-Cr-Dy oxides-based varistors were investigated with Dy$_2$ $O_3$ content in the range of 0.0∼2.0 ㏖%. As Dy$_2$ $O_3$ content is increased, the average grain size was decreased in the range of 18.2∼4.6 $\mu\textrm{m}$ and the ceramic density was decreased in the range of 5.49∼4.64 g/㎤. The incorporation of Dy$_2$ $O_3$ markedly enhanced the nonlinear properties of varistors more than 9 times in nonlinear exponent, compared with the varistor without Dy$_2$ $O_3$ The varistor with 0.5∼1.0 ㏖% Dy$_2$ $O_3$ exhibited the high nonlinearity, in which the nonlinear exponent is above 55 and the leakage current is below 1.0 ${\mu}\textrm{A}$. The donor concentration and the density of interface states were decreased in the range of (4.66∼0.25)${\times}$10$\^$18//㎤ and (5.70∼1.39)${\times}$10$\^$12//$\textrm{cm}^2$, respectively, with increasing Dy$_2$ $O_3$ content. The minimum dielectric dissipation factor of 0.0023 was obtained for 0.5 ㏖% Dy$_2$ $O_3$, but further addition of Dy$_2$ $O_3$ increased it.

• Journal of the Korean Ceramic Society
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• v.40 no.11
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• pp.1067-1072
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• 2003

The electrical stability of the varistor ceramics composed of Zn-Pr-Co-Cr-Dy oxides-based varistors was investigated at 0.0∼2.0 mol% Dy$_2$O$_3$ content under DC accelerated aging stress. The ceramic density was increased up to 0.5 mol% Dy$_2$O$_3$ whereas further addition of Dy$_2$O$_3$ decreased sintered ceramic density. The density sailently affected the stability due to the variation of conduction path. The nonlinearity of varistor ceramics was greatly improved above 45 in the nonlinear exponent and below nearly 1.0 ${\mu}$A by incorporating Dy$_2$O$_3$. Under 0.95 V$\_$1mA/150$^{\circ}C$/24 h stress state, the varistor ceramics doped with 0.5 mol% Dy$_2$O$_3$ exhibited the highest electrical stability, in which the variation rates of varistor voltage, nonlinear exponent, and leakage current were -0.9%, -14.4%, and +483.3%, respectively. The variation rates of relative permittivity and dissipation factor were +7.1% and +315.4%, respectively. The varistors with further addition of Dy$_2$O$_3$ exhibited very unstable state resulting in the thermal runaway due to low density.