Effect of annealing on phase structure and degradation of a zinc oxide varistor with Si-additive

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

“…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.…”

“…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 . The correlation between resistance to electrical degradation and the distribution of impurities on the surface of ZnO grains was thus investigated.…”

Improvement in Nonlinear Properties and Electrical Stability of ZnO Varistors with B2O3 Additives by Nano‐Coating Method

“…As some literatures have reported, introducing monovalent ions, such as Na + , K + , and Ag + , and annealing processes have been proved to improve the electrical stability of ZnO ceramic varistors. However, these methods also cause the decrease in the nonlinear properties and an increase in the leakage current.…”

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

“…At present, the improvement of the electrical degradation of ZnO varistors can be achieved by adding several impurities, such as Si, Sb or by thermal annealing or humidity. 4,[8][9][10][11][12][13][14][15] Upon the addition of Sb 2 O 3 to a Bi-Mn-Coadded ZnO varistor, changes in the grain boundary structure such as the formation of a twin crystal of ZnO, the formation of Zn 2.33 Sb 0.67 O 4 -type spinel structures (hereafter, spinel particles), and changes in the orientation of ZnO grains and the crystal structure of Bi 2 O 3 occur. 9,10,[16][17][18] It has been reported that the changes in the grain boundary structure affect the electrical degradation characteristics of varistors as a result of the change in the mobility of oxide ions or Zn 2+ ions at grain boundaries and in ZnO grains near the grain boundary.…”

“…The decrease in the number of interstitial Zn 2+ ions or the phase transition of Bi 2 O 3 upon annealing causes the improvement of the electrical degradation. 4,13 However, the effect of Sb addition on the improvement of the electrical degradation of ZnO varistors upon annealing is not clarified. In this study, samples of thermally annealed Sb 2 O 3 -added ZnO varistors were prepared to investigate the effect of annealing on the tolerance characteristics of electrical degradation, and the relationship between the change in the grain boundary structure, such as the formation of spinel particles or the phase transition of the Bi 2 O 3 phase, and the electrical degradation characteristics were investigated.…”