The influence of area/volume ratio on microstructure and non-Ohmic properties of SnO2-based varistor ceramic blocks

Ramírez, M. A.; Fernández, J.F.; Rubia, M. D. La; Frutos, J. de; Bueno, Paulo Roberto; Longo, Elson; Varela, José Arana

doi:10.1007/s10854-008-9602-8

Cited by 13 publications

(16 citation statements)

References 21 publications

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“…Several advantages have been reported for the SCNCr system over the commercial ZnO‐based varistor. These advantages seem to be intimately related with the simple microstructure of the former, with the low concentration of additives necessary to attain electrical nonlinearity, 7 with the high refractivity of the oxides used, which minimizes losses due to evaporation, 10 with the high thermal conductivity (0.5 W·(K·cm) −1 ) which almost doubles of that of ZnO 11 and with the excellent mechanical properties 12 . All these features determine the behavior of the material; for instance, according to recent results, 12 the SCNCr system has proven highly stable against degradation phenomena.…”

Section: Introductionmentioning

confidence: 99%

Comparative Electrical Behavior at Low and High Current of SnO₂‐ and ZnO‐Based Varistors

Ramírez

Bassi

Parra

et al. 2008

Journal of the American Ceramic Society

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The complete I-V characteristics of SnO 2 -based varistors, particularly of the Pianaro system SCNCr consisting in 98.9%SnO 2 11%CoO10.05%Nb 2 O 5 10.05%Cr 2 O 3 , all in mol%, have been seldom reported in the literature. A comparative study at low and high currents of the nonohmic behavior of SCNCr-and ZnO-based varistors (modified Matsuoka system) is proposed in this work. The SCNCr system showed higher nonlinearity coefficients in the whole range of measured current. The electrical breakdown field (E b ) was twice as high for the SCNCr system (5400 V/cm) than for the ZnO varistor (2600 V/cm) due to a smaller average grain size of the former (4.5 lm) with respect to the latter (8.5 lm). Nevertheless, we consider that another important factor responsible for the high E b in the SCNCr system is the great number of electrically active interfaces (85%) as determined with electrostatic force microscopy (EFM). It was also established that the SCNCr system might be produced in disks of smaller dimensions than that of commercial ZnO-based product, with a 5.0 cm À1 minimal area-volume (A/V) ratio. The SCNCr reached the saturation current in a short time because of the high resistivity of the grains, which is five times higher than that of the grains in ZnO-based varistors.

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Section: Introductionmentioning

confidence: 99%

Comparative Electrical Behavior at Low and High Current of SnO₂‐ and ZnO‐Based Varistors

Ramírez

Bassi

Parra

et al. 2008

Journal of the American Ceramic Society

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“…The studied systems correspond to the commercial ZnO‐based varistor (modified Matsuoka system) with the composition 95.4% ZnO + 1.5% Sb 2 O 3 + 1% NiO + 0.1% SiO 2 + 0.5% (Bi 2 O 3 , SnO 2 , Co 2 O 3 , MnO) [ZnO], and to the SnO 2 ‐based system (Pianaro system) with the composition 98.9% SnO 2 + 1% CoO + 0.05% Nb 2 O 5 + 0.05% Cr 2 O 3 [SCNCr], where all dopants were given as molar percentages. The ceramic pellets were prepared from analytical grade raw materials by solid‐state reaction as described in previous works . Powders were prepared by the conventional mixed oxide method.…”

Section: Methodsmentioning

confidence: 99%

Degradation Analysis of the SnO₂ and ZnO‐Based Varistors Using Electrostatic Force Microscopy

et al. 2013

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The degradation phenomena of ZnO and SnO 2 -based varistors were investigated for two different degradation methods: DC voltage at increased temperature and degradation with 8/20 ls pulsed currents (lightning type). Electrostatic force microscopy (EFM) was used to analyze the surface charge accumulated at grain-boundary regions before and after degradation. Before the degradation process, 85% of the barriers are active in the SnO 2 system, while the ZnO system presents only 30% effective barriers. Both systems showed changes in the electrical behavior when degraded with pulses. In the case of the ZnO system, the behavior after pulse degradation was essentially ohmic due to the destruction of barriers (about 99% of the interfaces are conductive). After the degradation with 8/20 ls pulsed currents, the SnO 2 system still presents nonohmic behavior with a significant decrease in the quantity of effective barriers (from 85% to 5%). However, when the degradation is accomplished with continuous current, the SnO 2 system exhibits minimum variation, while the ZnO system degrades from 30% to 5%. This result indicates the existence of metastable defects of low concentration and/or low diffusion in the SnO 2 system. High energy is necessary to degrade the barriers due to defect annihilation in the SnO 2 system.

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“…The traditional modified Matsuoka's system 11 13 ZnO-based samples were sintered at 1180°C for 2 h and SnO 2 -based samples were sintered at 1300°C for 1 h. The apparent density of sintered samples was estimated by the Archimedes methodology and average grain sizes from scanning electron microscope images by means of interceptions method. A density value of the 99% comparatively to theoretical density of ZnO was measured for the zinc oxide sample, which showed 8.5 m average grain size.…”

Section: Methodsmentioning

confidence: 99%

Influence of degradation on the electrical conduction process in ZnO and SnO2-based varistors

Ponce¹,

Ramírez²,

Parra³

et al. 2010

Journal of Applied Physics

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The conduction process during degradation, promoted by the application of fixed dc bias voltage at different temperatures ͑thermal steady states͒ and current pulses 8 / 20 s on ZnO and SnO 2 -based varistors, was studied comparatively in the present work. The electrical properties of the varistor systems were highly damaged after degradation with current pulse 8 / 20 s. Variations on the potential barrier height and donor concentration were calculated by fitting the experimental data from impedance spectroscopy measurements assuming the formation of Schottky barriers at the grain boundaries and electrical conduction to occur due to tunneling and thermionic emission.

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The influence of area/volume ratio on microstructure and non-Ohmic properties of SnO2-based varistor ceramic blocks

Cited by 13 publications

References 21 publications

Comparative Electrical Behavior at Low and High Current of SnO₂‐ and ZnO‐Based Varistors

Comparative Electrical Behavior at Low and High Current of SnO₂‐ and ZnO‐Based Varistors

Degradation Analysis of the SnO₂ and ZnO‐Based Varistors Using Electrostatic Force Microscopy

Influence of degradation on the electrical conduction process in ZnO and SnO2-based varistors

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The influence of area/volume ratio on microstructure and non-Ohmic properties of SnO2-based varistor ceramic blocks

Cited by 13 publications

References 21 publications

Comparative Electrical Behavior at Low and High Current of SnO2‐ and ZnO‐Based Varistors

Comparative Electrical Behavior at Low and High Current of SnO2‐ and ZnO‐Based Varistors

Degradation Analysis of the SnO2 and ZnO‐Based Varistors Using Electrostatic Force Microscopy

Influence of degradation on the electrical conduction process in ZnO and SnO2-based varistors

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Product

Resources

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Comparative Electrical Behavior at Low and High Current of SnO₂‐ and ZnO‐Based Varistors

Comparative Electrical Behavior at Low and High Current of SnO₂‐ and ZnO‐Based Varistors

Degradation Analysis of the SnO₂ and ZnO‐Based Varistors Using Electrostatic Force Microscopy