Abstract:Los varistores basados en ZnO son dispositivos electrocerámicos caracterizados por una elevada respuesta eléctrica no lineal, que se origina en una microestructura funcional con unas características bien definidas. En el presente artículo de revisión se examina como ha tenido lugar el desarrollo de estos materiales desde su descubrimiento a principios de los años 70. No obstante, a pesar del importante avance tecnológico registrado desde entonces, numerosos aspectos básicos relacionados con su microestructura … Show more
“…According to the mapping of elements, it is observed that both the spinel phase (Zn 7 Sb 2 O 12 ) and the Bi-rich phase are segregated in the grain boundaries, and that Cr, Mn and Ni are mainly associated with the spinel phase, while Co is observed associated with both grains and grain boundaries. It has been indicated that the determining oxides in the high temperature reactions are ZnO, Bi 2 O 3 and Sb 2 O 3 , and that the rest of the dopants only act as secondary elements that dissolve and are incorporated into different phases formed [32]. Figure 6 shows the cross-sectional appearance and element mapping of the base ceramic varistor.…”
ZnO-based ceramic varistors have shown excellent electrical and dielectric properties due to their characteristics microstructures represented by the arrangement of their grains and grain boundaries that allow the absorption and flow of energy when subjected to an electrical surge. Their properties and characteristics depend on their chemical compositions and processing routes. Typical processing routes involve several stages of grinding and precalcination—which are time consuming processes. Because of this, this study proposes a simpler and cheaper alternative route for processing ceramic varistors. The alternative process proposed is the mixing of the precursor oxides by means of a hydrothermal treatment. The characteristics and properties of the synthesized ceramic varistors were evaluated by means of scanning electron microscopy, X-ray diffraction and impedance spectroscopy, considering the effect of the addition of rare earth oxides (La2O3, CeO2 and Nd2O3). The results showed that the mixing of the oxides through hydrothermal treatment produces ceramic varistors with characteristics and properties similar to those obtained by other processing routes. Furthermore, it was observed that the addition of rare earth oxides affects the characteristics and properties of the ceramic varistor depending on the type of rare earth oxide added, its concentration and ionic radius.
“…According to the mapping of elements, it is observed that both the spinel phase (Zn 7 Sb 2 O 12 ) and the Bi-rich phase are segregated in the grain boundaries, and that Cr, Mn and Ni are mainly associated with the spinel phase, while Co is observed associated with both grains and grain boundaries. It has been indicated that the determining oxides in the high temperature reactions are ZnO, Bi 2 O 3 and Sb 2 O 3 , and that the rest of the dopants only act as secondary elements that dissolve and are incorporated into different phases formed [32]. Figure 6 shows the cross-sectional appearance and element mapping of the base ceramic varistor.…”
ZnO-based ceramic varistors have shown excellent electrical and dielectric properties due to their characteristics microstructures represented by the arrangement of their grains and grain boundaries that allow the absorption and flow of energy when subjected to an electrical surge. Their properties and characteristics depend on their chemical compositions and processing routes. Typical processing routes involve several stages of grinding and precalcination—which are time consuming processes. Because of this, this study proposes a simpler and cheaper alternative route for processing ceramic varistors. The alternative process proposed is the mixing of the precursor oxides by means of a hydrothermal treatment. The characteristics and properties of the synthesized ceramic varistors were evaluated by means of scanning electron microscopy, X-ray diffraction and impedance spectroscopy, considering the effect of the addition of rare earth oxides (La2O3, CeO2 and Nd2O3). The results showed that the mixing of the oxides through hydrothermal treatment produces ceramic varistors with characteristics and properties similar to those obtained by other processing routes. Furthermore, it was observed that the addition of rare earth oxides affects the characteristics and properties of the ceramic varistor depending on the type of rare earth oxide added, its concentration and ionic radius.
“…Finally, in the last region (the high-current region) characterized by grain control, the current-voltage characteristics are linear again as occurs in the first region. Since zinc oxide [ZnO] material was introduced by Matsuoka (1971), it has been the most extensively studied material and used as the base for ceramic systems, consequently it became the most important ceramic for commercial production of varistors (Clarke, 1999;Peiteado, 2005;Wang et al, 2003;Kale et al, 1999;Matsuoka, 1971). Due to the need of attaining varistors with better properties, there has recently been a great interest in other ceramic materials, e.g.…”
“…Estos materiales actúan como dispositivo para la protección de equipos electrónicos y su función es desviar los sobrevoltajes; la principal función de estos dispositivos es mantener el valor de potencial eléctrico cuando ocurre un gran aumento en la intensidad del campo eléctrico aplicado (1). Esto se puede expresar a través de la ecuación I=KV α , donde α es el coeficiente de no-linealidad, parámetro muy importante para la caracterización de los varistores (2).…”
El óxido de estaño ha despertado gran interés científico y tecnológico por su potencial uso en la obtención varistores. Con el fin de mejorar las propiedades microestructurales y eléctricas que estos dispositivos presentan se viene estudiando el efecto de incorporar diferentes dopantes, entre ellos el TiO 2 y la Al 2 O 3 . El efecto que estos óxidos tienen sobre el comportamiento de los varistores del sistema Sn-Co-Nb-Ti-Al, obtenidos a través del método de precursor polimérico (Pechini), fue investigado en este trabajo. La materia prima sintetizada se caracterizó utilizando Difracción de Rayos X (DRX) y Microscopía Electrónica de Barrido (MEB). Muestras sinterizadas se caracterizaron microestructural y eléctricamente encontrándose que el TiO 2 , aparentemente, favorece el crecimiento de grano y la Al 2 O 3 contribuye a la disminución del mismo, efecto que se manifiesta en los varistores con base en Sn-Co-Nb. El campo de ruptura se incrementó hasta los 6300V/cm al aumentar el contenido de Al 2 O 3 y se obtuvieron coeficientes de no-linealidad de 22.
Influence of TiO 2 and Al 2 O 3 on the electrical and microstructural properties of SnO 2 ceramics obtained by the Pechini methodTin oxide has wakened up great scientific and technological interest for its potential use in varistors production and as gas sensor. In order to improve the microstructural and electrical properties in SnO 2 varistor ceramics, the influence of differents dopants used, like TiO 2 and Al 2 O 3 , is under research. The effect of TiO 2 and Al 2 O 3 on the properties of Sn-Co-Nb varistor systems obtained by the Pechini method has been investigated in this work. Characterization of synthesized raw material was performed by X-Ray Diffraction (XRD) and Scanning Electronic Microscopy (SEM). The microstructural and electrical characterization of sintered samples show that the TiO 2 favors the grain growth and the Al 2 O 3 contributes to the decrease it, effect that is manifested in the Sn-Co-Nb varistor systems. Breakdown field increase up to 6300V/cm with increasing Al 2 O 3 content and non-linear coefficients with α=22 were obtained.
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