Characterization of ZnO-degraded varistors used in high-tension devices

Ramírez, M. A.; Simões, Alexandre Zirpoli; Márquez, María del Carmen Bellido; Maniette, Y.; Cavalheiro, Alberto Adriano; Varela, José Arana

doi:10.1016/j.materresbull.2006.09.001

Cited by 29 publications

(30 citation statements)

References 24 publications

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“…2a-d). Ramîrez found that the potential barrier formed in the region between two adjacent ZnO grains is more effective than that in the spinel-ZnO junction [25], which means the ZnO grains surrounded by the bismuth oxide and spinel phases present a larger number of non-effective barriers. Furthermore, the decrease of breakdown voltage per grain boundary (V gb ) is also responsible for the decrease of E 1 mA=cm 2 .…”

Section: Resultsmentioning

confidence: 99%

Effect of Zn doping on stability of ZnO varistors under high pulse-current stress

Jiang

Wang

Zhang

et al. 2015

Ceramics International

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Section: Resultsmentioning

confidence: 99%

Effect of Zn doping on stability of ZnO varistors under high pulse-current stress

Jiang

Wang

Zhang

et al. 2015

Ceramics International

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“…In ZnO.Bi 2 O 3 -based varistor systems, changes also occur in both phases, the amorphous and crystalline phase of Bi 2 O 3 during the processing or its useful life 7,20 . The varistors submitted to different stresses during use can modify its crystalline structure, which can cause the degradation process 7 . Figures 4a and 4b show Nyquist complex impedance diagrams for ZPC system with 0.1 and 1 mol% of Pr 6 O 11 and sintered at 1300 and 1350 °C respectively.…”

Section: Resultsmentioning

confidence: 99%

“…In fact, the history of Pr 6 O 11 -based ZnO varistors is similar to the Bi 2 O 3 -based ZnO varistors 5 , but they have not been adequately studied. However, the Pr 6 O 11 -based ZnO varistors don't have volatilization of components 3 and they own a simpler microstructure when compared with Bi 2 O 3 -based varistors, which is an important fact for the stability and degradation phenomena [6][7][8][9] . Most of commercial ZnO varistors are ZnO-Bi 2 O 3 -based varistor ceramics, possessing as major additive Bi 2 O 3 .…”

Section: Introductionmentioning

confidence: 99%

Microstructural and nonohmic properties of ZnO.Pr6O11 CoO polycrystalline system

et al. 2010

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the effective cross-section area of the elements is increased 14 . Several studies describe the dependence of varistor properties on processing conditions of Pr-doped ZnO varistors, especially in the field of grain boundary formation [2][3][4] 13 . It is very important to understand the structure, composition and properties of the boundaries since they have a strong influence on electrical properties. Our purpose is to investigate the microstructure, the current density-electric field (J vs. E) characteristics, and the capacitance-voltage (C-V) characteristics of ZPC varistor systems. Experimental ProcedureThe varistor systems (95-x) mol% ZnO + x mol% Pr 6 O 11 + 5 mol% CoO (x = 0.1, 0.5 and 1.0) were prepared from the mixture of oxide precursors method, all of them being analytical grade oxides: ZnO (Aldrich-99.99%), Pr 6 O 11 (Aldrich-99.9%) and CoO (Riedel-99.9%). The starting materials were attrition-milled in water for 3 hours. Then the dry slurry was calcined at 750 °C in air for 2 hours. The calcined powders were pulverized using agate mortar and pestle and after 2 wt. (%) polyvinyl alcohol (PVA) binder addition, granulated by sieving 200-mesh screen to produce the starting powder. The powder was uniaxially pressed into discs of 12 mm diameter and 1 mm thickness at a pressure of 80 MPa. The pellets were sintered at 1300 and 1350 °C for 2 hours with a heating rate of 5 °C/min followed by furnace cooling. The samples were characterized by X-ray diffraction (XRD, Rigaku, 20-2000), 40 kV and 150 mA from 2θ (20 to 80°), ∆2θ = 0.02°, with Cukα wavelength monocromatized by a graphite crystal. To obtain the Scanning Electron Microscopy (SEM) micrographies (ZEISS ® DSM 940 A) the sintered samples were polished and thermally etched by heating at 100 °C below the IntroductionZnO varistor ceramics are resistor devices manufactured by sintering ZnO powder containing various minor additives 1 . It has been recognized that at least two different classes of additives must be added to the ceramic varistors in order to obtain good nonohmic characteristics 2 . The first class of such additives are varistor-forming oxides (VFO), such as Bi 2 O 3 , Pr 6 O 11 , La 2 O 3 , BaO, V 2 O 5 and glass frits. The second class of additives are 3d transition-metal oxides, which improve significantly the nonohmic characteristics 3 . Zinc oxide ceramics, containing Pr 6 O 11 and CoO, which exhibit current nonohmic characteristics, were first reported by Mukae et al. 4 . In fact, the history of Pr 6 O 11 -based ZnO varistors is similar to the Bi 2 O 3 -based ZnO varistors 5 , but they have not been adequately studied. However, the Pr 6 O 11 -based ZnO varistors don't have volatilization of components 3 and they own a simpler microstructure when compared with Bi 2 O 3 -based varistors, which is an important fact for the stability and degradation phenomena [6][7][8][9] . Most of commercial ZnO varistors are ZnO-Bi 2 O 3 -based varistor ceramics, possessing as major additive Bi 2 O 3 . Although they exhibit excellent varistor perform...

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“…La formulación de estos cerámicos basados en ZnO comprende un complejo sistema multicomponente en el cual los dopantes juegan un papel muy importante, y debido a que el comportamiento varistor se origina en la estructura electrónica de los bordes de grano, la manipulación y el control de la microestructura en los bordes de grano se ve reflejada directamente en el desempeño eléctrico del varistor (4)(5)(6)(7)(8). Así por ejemplo para aplicaciones de alto voltaje se requiere de una microestructura fina constituida por pequeños granos de ZnO, para lo cual se incorpora Sb 2 O 3 como inhibidor del crecimiento de dichos granos, sistema ZnO-Bi 2 O 3 -Sb 2 O 3 (9)(10)(11)(12). Por el contrario los varistores de bajo voltaje se caracterizan por una microestructura de granos gruesos, y para ello se suele añadir TiO 2 como dopante promotor del crecimiento de grano, sistema ZnO-Bi 2 O 3 -TiO 2 (13)(14)(15)(16)(17).…”

Section: Introductionunclassified

Control microestructural en varistores cerámicos basados en el sistema ZnO-Bi2O3-Sb2O3 dopados con TiO2

Cruz¹,

Gallego²,

Fernández-Hevia³

et al. 2012

Bol. Soc. Esp. Ceram. Vidr.

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Típicamente el Óxido de Titanio se incorpora a la formulación de varistores basados en ZnO dopado con Bi 2 O 3 para favorecer un crecimiento de los granos de ZnO, lo que determina su aplicación en dispositivos de bajo voltaje. Sin embargo su incorporación en formulaciones basadas en el ternario ZnO-Bi 2 O 3 -Sb 2 O 3 (sistema ZBS), características de aplicaciones de alto voltaje, es algo que apenas se ha analizado. En este trabajo se ha comprobado que lejos de favorecer el crecimiento de los granos de ZnO, la incorporación de TiO 2 a sistemas basados en dicho ternario ZBS lleva a un mayor control de la microestructura de estos electrocerámicos, y esto además se traduce en una apreciable mejoría de su respuesta eléctrica. Typically Titanium oxide is added to the formulation of Bi 2 O 3 -doped ZnO based varistors to enhance the growth of ZnO grains, thus allowing their application in low voltage devices. However its incorporation to formulation based on the ZnOBi 2 O 3 -Sb 2 O 3 (ZBS system), characteristic of high voltage applications has not been analyzed jet. In this contribution it has been verified that far from promoting the ZnO grain growth, the incorporation of TiO 2 to varistor formulations based on this ZBS ternary system leads to a better control of the varistor microstructure, which in turns causes an appreciable improvement of its electrical response.Key words: ZnO varistors, microstructure, spinel, grain growth. INTRODUCCIÓNLos varistores, o resistores variables, son dispositivos de estado sólido cuya resistencia es dependiente del voltaje, corriente o polaridad (1-3). El varistor cerámico es de gran importancia tecnológica por sus características eléctricas no lineales, lo que permite que sea utilizado como interruptor reversible en circuitos de estado sólido con la capacidad adicional de almacenar energía. Concretamente los varistores basados en Óxido de Cinc dopado con Bi 2 O 3 son los más comunes por su amplio rango de voltaje y su elevado rendimiento no lineal (1). La formulación de estos cerámicos basados en ZnO comprende un complejo sistema multicomponente en el cual los dopantes juegan un papel muy importante, y debido a que el comportamiento varistor se origina en la estructura electrónica de los bordes de grano, la manipulación y el control de la microestructura en los bordes de grano se ve reflejada directamente en el desempeño eléctrico del varistor (4-8). Así por ejemplo para aplicaciones de alto voltaje se requiere de una microestructura fina constituida por pequeños granos de ZnO, para lo cual se incorpora Sb 2 O 3 como inhibidor del crecimiento de dichos granos, sistema ZnO-Bi 2 O 3 -Sb 2 O 3 (9-12). Por el contrario los varistores de bajo voltaje se caracterizan por una microestructura de granos gruesos, y para ello se suele añadir TiO 2 como dopante promotor del crecimiento de grano, sistema ZnO-Bi 2 O 3 -TiO 2 (13-17). En este último caso se ha Vol 51, 1, 61-66, Enero-Febrero 2012 ISSN 0366-3175. eISSN 2173-0431. doi: 10.3989/cyv.092012 comprobado que los iones de Titanio se distri...

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Characterization of ZnO-degraded varistors used in high-tension devices

Cited by 29 publications

References 24 publications

Effect of Zn doping on stability of ZnO varistors under high pulse-current stress

Effect of Zn doping on stability of ZnO varistors under high pulse-current stress

Microstructural and nonohmic properties of ZnO.Pr6O11 CoO polycrystalline system

Control microestructural en varistores cerámicos basados en el sistema ZnO-Bi<sub>2</sub>O<sub>3</sub>-Sb<sub>2</sub>O<sub>3</sub> dopados con TiO<sub>2</sub>

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