• Transactions on Electrical and Electronic Materials
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• 제16권4호
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• pp.221-225
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• 2015

The sintering effect on the microstructure, electrical properties, and dielectric characteristics of ZnO-V₂O₅-MnO₂-Nb₂O₅-Dy₂O₃-based ceramics was investigated. With the increase of sintering temperature from 875 to 950℃, the density of the sintered pellets decreased from 5.57 to 5.45 g/cm³ and the average grain size increased from 4.3 to 10.9 μm. The breakdown field decreased noticeably from 6,095 to 996 V/cm with the increase of sintering temperature. The varistor ceramics sintered at 900℃ exhibited the best nonlinear properties: 39.2 in the nonlinear coefficient and 0.24 mA/cm² in the leakage current density. The dielectric constant increased sharply from 658.6 to 2,928.8 with the increase of sintering temperature. On the whole, the dissipation factor exhibited a fluctuation with the increase of the sintering temperature, and a minimum value of 0.284 at 900℃.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.415-418
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• 2001

The I-V characteristics and its stability of ZPCCL-based ceramic varistors doped with La$_2$O$_3$in the range of 0.0~4.0 mol% were investigated. The density of ceramics was increased in the range of 4.7~5.8 g/cm$^3$ with increasing La$_2$O$_3$content. As La$_2$O$_3$content is increased, the varistor voltage was decreased in the range of 503.49-9.42 V/mm up to 2.0 mol%, whereas increasing La$_2$O$_3$content further caused it to increase. The ZPCCL-based varistors were characterized by nonlinearity, in which the nonlinear exponent is in the range of 3.05~82.43 and leakage current is in the range of 0.24-100.22 $\mu$A. Among ZPCCL-based varistors, 0.5 mol% added-varistors exhibited an excellent nonlinearity, in which the nonlinear exponent is 82.43 and the leakage current is 0.24 $\mu$A. Furthermore, they exhibited a high stability, in which the variation rate of the varistor voltage and the nonlinear exponent was -1.11% and -6.72%, respectively, under DC 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)+(0.95 V$_{1mA}$1$25^{\circ}C$//12h)+(0.95 V$_{1mA}$15$0^{\circ}C$//12h). Consequently, it was estimated that ZPCCL-based ceramics will be applied to development of Pr$_{6}$O$_{11}$ based ZnO varistors having a high performance.e.rformance.e.

• 한국전기전자재료학회논문지
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• 제14권10호
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• pp.808-814
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• 2001

The electrical properties and stabiltiy of Pr$_{6}$O$_{11}$ -based ZnO varistors, which are composed of ZnO-Pr$_{6}$O$_{11}$-Cr$_{2}$O$_{3}$-Er$_{2}$O$_{3}$ based ceramics, were investigated in the Er$_{2}$O$_{3}$ content range of 0.5 to 2.0 mol%. As Er$_{2}$O$_{3}$content is increased up to approximaterly 1.0mol%, the nonlinearity was decreased. Increasing Er$_{2}$O$_{3}$ content further caused the nonlinearity to increase. The varistors with 2.0 mol% Er$_{2}$O$_{3}$ exhibited a high nonlinearity, in which the nonlinear exponent is 47.41 and the leakage current is 1.82 $\mu$A. Furthermore, they showed a very excellent stability, in which the variation rates of the varistor voltage, the nonlinear exponent, and leakage current are -0.52%, -4.09%, and 152.75%, respectively, under DC accelerated aging 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)+(0.95 V$_{1mA}$1$25^{\circ}C$/12h)+(0.95 V$_{1mA}$1$25^{\circ}C$/12h).2h).TEX>/12h).2h).

• Transactions on Electrical and Electronic Materials
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• 제7권3호
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• pp.123-128
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• 2006

The microstructure and electrical properties of the varistors, which are composed of $ZnO-Pr_6O_{11}-CoO-Cr_2O_3-La_2O_3-based$ ceramics, were investigated for different $La_2O_3$ contents. The increase of $La_2O_3$ content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0 mol%. The highest nonlinearity was obtained from 0.5 mol% $La_2O_3$, with the nonlinear coefficient of 81.6 and the leakage current of $0.2{\mu}A$. The increase of sintering time and temperature greatly decreased the nonlinear properties. As the $La_2O_3$ content increased, the donor density increased from $0.64\times10^{18}/cm^3\;to\;16.89\times10^{18}/cm^3$ and the barrier height greatly decreased with increasing $La_2O_3$ content, reaching a maximum (1.47 eV) in 0.5 mol% $La_2O_3$.

• 한국재료학회지
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• 제30권10호
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• pp.502-508
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• 2020

This paper focuses on the electrical properties and stability against DC accelerated aging stress of ZnO-V₂O₅-MnO₂-Nb₂O₅-Bi₂O₃-Co₃O₄-Dy₂O₃ (ZVMNBCD) varistor ceramics sintered at 850 - 925 ℃. With the increase of sintering temperature, the average grain size increases from 4.4 to 11.8 mm, and the density of the sintered pellets decreases from 5.53 to 5.40 g/㎤ due to the volatility of V₂O₅, which has a low melting point. The breakdown field abruptly decreases from 8016 to 1,715 V/cm with the increase of the sintering temperature. The maximum non-ohmic coefficient (59) is obtained when the sample is sintered at 875 ℃. The samples sintered at below 900 ℃ exhibit a relatively low leakage current, less than 60 mA/㎠. The apparent dielectric constant increases due to the increase of the average grain size with the increase of the sintering temperature. The change tendency of dissipation factor at 1 kHz according to the sintering temperature coincides with the tendency of the leakage current. In terms of stability, the samples sintered at 900 ℃ exhibit both high non-ohmic coefficient (45) and excellent stability, 0.8% in 𝚫E_B/E_B and -0.7 % in 𝚫α/α after application of DC accelerated aging stress (0.85 E_B/85 ℃/24 h).

• 한국분말재료학회지
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• 제17권4호
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• pp.289-294
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• 2010

For the aim of low-temperature co-fired ceramic microwave components, sintering behavior and microwave properties (dielectric constant ${\varepsilon}_r$, quality factor Q, and temperature coefficient of resonant frequency ${\tau}_f$) are investigated in $Bi_{18}O(Ca_{0.725}Zn_{0.275})_8Nb_{12}O_{65}$ [BCZN] ceramics with addition of $V_2O_5$. The specimens are prepared by conventional ceramic processing technique. As the main result, it is demonstrated that the additives ($V_2O_5$) show the effect of lowering of sintering temperature and improvement of microwave properties at the optimum additive content. The addition of 0.25 wt% $V_2O_5$ lowers the sintering temperature to $890^{\circ}C$ utilizing liquidphase sintering and show the microwave dielectric properties (dielectric constant ${\varepsilon}_r$ = 75, quality factor $Q{\times}f$ = 572 GHz, temperature coefficient of resonance frequency ${\tau}_f\;=\;-10\;ppm/^{\circ}C$). The estimated microwave dielectric properties with $V_2O_5$ addition (increase of ${\varepsilon}_r$, decrease of $Q{\times}f$, shift of ${\tau}_f$ to negative values) can be explained by the observed microstrucure (sintered density, abnormal grain structure) and possibly high-permittivity $Bi_{18}Zn_8Nb_{12}O_{65}$ (BZN) phase determined by X-ray diffraction.

• 한국전기전자재료학회논문지
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• 제13권9호
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• pp.735-744
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• 2000

The electrical procerties and stability of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Er$_2$O$_3$ (ZPCCE) based varistors were investigated in the Er$_2$O$_3$content range of 0.0 to 4.0 mol%. ZPCCE ceramics containing 2.0 mol% Er$_2$O$_3$ exhibited the highest density of 5.74 g/㎤ corresponding to 99.3% of theoretical density. The varistors with 0.5 mol% and 2.0 mol% Er$_2$O$_3$exhibited a relatively satisfying nonlinearity, which the nonlinear exponent is 40.50 and 47.15, respectively and the leakage current is 2.66 $mutextrm{A}$, respectively. 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)+(0.95 V$_{1mA}$1$25^{\circ}C$12h), they showed a very excellent stability, which the variation rate of the variator voltage is -0.89% and -0.15%, the variation rate of the nonlinear coefficient is -4.67% and -3.56%, and the variation rate of leakage current is -6.02% and -19.56%, respectively. It is surely bellived that ZnO-0.5 mol% Pr$_{6}$O$_{11}$-1.0 mol% CoO-0.5 mol% Cr$_2$O$_3$-x mol% Er$_2$O$_3$(x=0.5, 2.0) based varistors will be greatly contributed to develop the advanced Pr$_{6}$O$_{11}$-based ZnO varistors in future.uture. future.uture.

• Transactions on Electrical and Electronic Materials
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• 제7권4호
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• pp.189-195
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• 2006

The microstructure, electrical and dielectric properties, and stability against DC accelerated aging stress of the varistors, which are composed of quaternary system $ZnO-Pr_6O_{11}CoO-Cr_2O_3-based$ ceramics, were investigated for different $La_2O_3$ contents. The increase of $La_2O_3$ content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0mol%. The highest nonlinearity was obtained from 0.5mol% $La_2O_3$, with the nonlinear coefficient of 81.6 and the leakage current of $0.1{\mu}A$. The varistors doped with 0.5mol% $La_2O_3$ exhibited high stability, in which the variation rates of breakdown voltage, nonlinear coefficient, leakage current, dielectric constant, and dissipation factor were -1.1%, -3.7%, +100%, +1.4%, and +8.2%, respectively, for stressing state of $0.95V_{1mA}/150^{\circ}C/24h$.

• 한국전기전자재료학회논문지
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• 제16권12호
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• pp.1071-1076
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• 2003

The nonlinear properties and their stability of ZPCCD- based varistors, which are composed of ZnO P $r_{6}$ $O_{ll}$ - CoO-C $r_2$ $O_3$-D $y_2$ $O_3$-based ceramics, were investigated in the D $y_2$ $O_3$ content range of 0.0∼2.0 mol%. The incorporation of D $y_2$ $O_3$ greatly affected the nonlinear properties and the best nonlinearity was obtained from 0.5 mol% D $y_2$ $O_3$ with nonlinear exponent of 66.6 and leakage current of 1.2 $\mu$A. Further addition of D $y_2$ $O_3$ deteriorated the nonlinear properties. In stability against DC accelerated aging stress state: 0.95 $V_{1mA}$/15$0^{\circ}C$/24 h, the 0.5 mol％ D $y_2$ $O_3$-doped varistor exhibited the highest stability, in which the variation rate of varistor voltage and nonlinear exponent are -1.9% and 10.5%, respectively. The remainder varistors resulted in thermal runaway due to low density of ceramics.s.s.

• 한국전기전자재료학회논문지
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• 제15권3호
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• pp.244-252
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• 2002

The electrical and dielectric behavior fort DC accelerated aging stress of P $r_{6}$ $O_{11}$-based Zno varistors cnsisting of ZnO-P $r_{6}$ $O_{11}$-CoO-C $r_2$ $O_3$-E $r_2$ $O_3$ were investigated with sintering temperature in the range of 1325~1345$^{\circ}C$. The varistor ceramics with increasing sintering temperature were more densified. A more densified varistors leaded to high stability for DC accelerated aging stress. Furthermore, the stability for DC accelerated aging stress was increased with the leakage current and dtan $\delta$/dV decreasing in order of 1325longrightarrow1335longrightarrow1345longrightarrow134$0^{\circ}C$ in sintering temperature. It was found that the stability for DC stress is affected more greatly by the leakage current and dtan $\delta$/dV than the densification. It is considered that the stability of varistors for DC stress can be estimated by considering the factors, such as the densification, leakage current, and dtan $\delta$/dV. As a result, the varistor sintered at 134$0^{\circ}C$ exhibited the highest stability, with %$\Delta$ $V_{lmA}$=-1.54%, %$\Delta$$\alpha$=-2.49%, %$\Delta$ $I_{\ell}$=+240.68%, 5%$\Delta$tan$\delta$=+29.96%.96%.96%.%.