• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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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 (0.85 V$_{1mA}$/115$^{\circ}C$/24h)+(0.90 V$_{1mA}$/12$0^{\circ}C$/24h)+(0.95 V$_{1mA}$/1$25^{\circ}C$/24h)+(0.95 V$_{1mA}$/15$0^{\circ}C$/24h). Next the varistors doped with 2.0 mol% exhibiting the nonlinear exponent of 47.39 showed high stability,ity,ability,ity,

• 한국전기전자재료학회논문지
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• 제13권3호
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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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 영호남학술대회 논문집
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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.

• 한국전기전자재료학회논문지
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• 제13권8호
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• pp.667-674
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• 2000

The stability of ZnO-Pr$_{6}$/O$_{11}$-CoO-Er$_{2}$/O$_3$based varistors was investigated with Er$_{2}$/O$_3$additive content of the range 0.0 to 2.0 mol%. All varistors sintered at 130$0^{\circ}C$ exhibited the thermal runaway within short times even under weak d.c. stress. As a result these varistors were completely degraded. On the contrary the stability of varistors sintered at 135$0^{\circ}C$ was far better than that of 130$0^{\circ}C$. In particular the varistors added with 0.5mol% Er$_{2}$/O$_3$ which the nonlinear exponent is 34.83 and the leakage current is 7.38 $mutextrm{A}$ showed a excellent stability which the variation rate of the varistors voltage the nonlinear coefficient and the leakage current is below 1%, 2%, and 3.5% respectively even under more severe d.c. stress such as (0.80 V$_{1mA}$9$0^{\circ}C$/12h)+(0.85 V$_{1mA}$115$^{\circ}C$/12h)+(0.90 V$_{1mA}$12$0^{\circ}C$12h) Consequently it is estimated that the ZnO-0.5 mol% Pr$_{6}$/O sub 11/-1.0 mol% CoO-0.5 mol% Er$_{2}$/O sub 3/ based varistors will be used to develop the advanced Pr$_{6}$/O$_{11}$-1.0 mol% CoO-0.5 mol% Er$_{2}$/O$_{3}$ based varistors will be used to develop the advanced Pr$_{6}$/O$_{11}$-based ZnO varistors having the high performance and stability in future. future.ure. future.

• 한국전기전자재료학회논문지
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• 제14권8호
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• pp.640-646
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• 2001

The electrical stability for DC stress of Pr$_{6}$O$_{11}$-based ZnO varistos consisting of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Er$_2$O$_3$-based ceramics were investigated with sintering temperature in the range of 1325~1345$^{\circ}C$. A the sintering temperature is raised, the nonlinear exponent of varistors was decreased, whereas the stability was markedly improved. The density of ceramics was found to greatly affect the electrical stability for DC stress. The varistors sintered at 13$25^{\circ}C$ were completely degraded because of thermal runaway attributing to low density. The varistors sintered at 1335$^{\circ}C$ exhibited the highest nonlinearity, with a nonlinear exponent of 70.53 and a leakage current of 1.92$\mu$A, whereas they did not exhibit relatively high stability. On the contrary, the varistors sintered at >134$0^{\circ}C$ exhibited not only a high nonlinearity marking the nonlinear exponent above 50 and the leakage current below 3$\mu$A, but also a high stability marking the variation rate of the varistor voltage below 2%, even under DC stress such as (0.80V$_{1mA}$/9$0^{\circ}C$/12h)+(0.85V$_{1mA}$/115$^{\circ}C$/12h)+(0.90V$_{1mA}$/12$0^{\circ}C$/12h)+(0.95V$_{1mA}$/1$25^{\circ}C$/12h)+(0.95V$_{1mA}$/15$0^{\circ}C$/12h). In particular, ti was found that the varistors sintered at 134$0^{\circ}C$ were more nonlinear and more stable, compared with that of 1345$^{\circ}C$.EX>.}C$.EX>.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 C
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• pp.1003-1007
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• 1999

This paper is reported for the stability of ZnO-$Pr_{6}O_{11}-CoO-Er_{2}O_{3}$ based ceramic varistors with $Er_{2}O_{3}$ added in the addition range 0.0 to 2.0 mol%. The varistors sintered at $130^{\circ}C$ exhibited abrupt positive current creep phenomena, which accompany thermal run away within short times, even under weak d.c. stress. As a result, these varistors were completely degraded. On the contrary, the stability of varistors sintered at $1350^{\circ}C$ was far better than that of $1300^{\circ}C$. In particular, the varistor containing 0.5 mol% $Er_{2}O_{3}$ showed a excellent stability, which the variation rate of the varistor voltage, the nonlinear coefficient, and leakage current is below 1%, 2%, and 3.5%, respectively, even under more severe d.c. stress, such as ($0.8V_{1mA}/90^{\circ}C/12h$) + ($0.85V_{1mA}/115^{\circ}C/12h$) + ($0.9V_{1mA}/120^{\circ}C/12h$) + ($0.9V_{1mA}/150^{\circ}C/12h$). Consequently, it is estimated that the basic composition of ZnO-$Pr_{6}O_{11}-CoO-Er_{2}O_{3}$ based varistor contain 0.5 mol% $Er_{2}O_{3}$ will be used to the fabrication of the varistors for high performance and stability in a forthcoming.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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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 ${\mu}s$).

• 한국전기전자재료학회논문지
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• 제20권6호
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• pp.508-513
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• 2007

The electrical properties and stability of $ZnO-Pr_6O_{11}-CoO-Cr_2O_3-based$ varistors were investigated for different $Tb_4O_{11}$ amounts in the range of $0{\sim}1.0\;mol%$. As the $Tb_4O_{11}$ amount increased, the sintered density increased in the range of $99.1{\sim}101.1%$ of theoretical density and the average grain size decreased in the range of $7.7{\sim}4.8{\mu}m$. The varistor voltage increased in the range of $280.9{\sim}715.8V/mm$ and the nonlinear coefficient increased in the range of $26.4{\sim}44.4$ with the increased of $Tb_4O_{11}$ amount. The 0.25 mol% $Tb_4O_{11}$-doped varistors exhibited the high electrical stability, with -0.1% in variation rate of varistor voltage, -0.7% in variation rate of nonlinear coefficient, and +17.4% in variation rate of leakage current for specified dc accelerated aging stress of $0.95V_{1mA}/150^{\circ}C/24h$.

• 한국전기전자재료학회논문지
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• 제17권9호
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• pp.924-929
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• 2004

The microstructure, electrical and dielectric characteristics of $ZnO-{Pr}_6{O}_11-{CoO}-{Dy}_2{O}_3$-based varistors were investigated without and with various metal oxide additives(NiO, MgO, Cr$_2$O$_3$). The average grain size decreased in the range of 18.4 $\backsim$ 11.5 $\mu$m, in order of NiO\longrightarrowMgO\longrightarrow{Cr}_2{O}_3$ and the density decreased in the range of 5.62 \backsim 5.33 $g/{cm}^3$ in order of NiO\longrightarrowCr$_2$O$_3$\longrightarrowMgO. While, the nonlinear exponent increased In the range of 19.8$\backsim$67.4 in order of NiO\longrightarrowMgO\longrightarrow${Cr}_2{O}_3$ and the leakage current decreased in the range of 25.6 $\backsim$ 1.2 $\mu$A in order of NiO\longrightarrow${Cr}_2{O}_3$\longrightarrowMgO. Among all varistors, the Cr$_2$O$_3$-added varistor exhibited the highest nonlinearity, with a nonlinear exponent of 67.4 and a leakage current of 1.2 $\mu$A. Furthermore, this varistor exhibited the lowest dielectric dissipation factor of 0.0407.

• Transactions on Electrical and Electronic Materials
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• 제13권5호
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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.