Effect of thermal annealing on electrical degradation characteristics of Sb–Bi–Mn–Co-added ZnO varistors

Relation Between Grain Boundary Structure and Electrical Degradation in Zinc Oxide Varistors

“…Therefore, three different samples with added SiO 2 or Sb 2 O 3 , which are widely used additives for ZnO varistors, as well as both Sb 2 O 3 and SiO 2 added simultaneously to the basic varistor were prepared and the form of the Bi 2 O 3 deposit on the surface of grain boundary fracture of ZnO was investigated. It was confirmed using EDS that all additives added further to the basic varistor coexisted with Bi at grain boundaries or triple points . Moreover, it has been reported that the size of a ZnO grain becomes smaller by the addition of Sb 2 O 3 .…”

“…After sintering, Samples 1–5 were cooled naturally to room temperature in the electric furnace. The electrical degradation was found to recover, or in other words, the resistance to electrical degradation was improved, by the thermal treatment . Furthermore, samples with the same composition as Sample 2 were thermally treated using three different cooling histories after sintering.…”

“…Moreover, the resolution of a BSE detector is higher than that of EDS because the area of fluorescent X‐rays generated by electron irradiation is more widespread than that of BSEs. In a previous study, the microstructure of a polished surface of a ZnO varistor was observed macroscopically using a BSE detector with SEM . However, the distribution of impurities on the surface of ZnO grains has not been observed microscopically.…”

“…The microscopic distribution of impurities can be obtained by observing the grain boundary fracture surface. To observe the fractured surfaces of ZnO grains with uniform size, Sb 2 O 3 was added to the ZnO varistor to prevent grain growth and avoid nonuniform grain size . Since it has been reported that the addition of SiO 2 to a Bi‐added ZnO varistor improved its resistance to electrical degradation, SiO 2 was added to the ZnO varistor .…”

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

“…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)(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).…”