Non-uniform ageing behavior of individual grain boundaries in ZnO varistor ceramics

Electrical degradation of double-Schottky barrier in ZnO varistors

“…Summarized Degradation Mechanism Eda et al [16][17][18] ion migration process Takahashi et al 19 chemical desorption of oxygen ions at the grain boundaries Chiang et al 20 asymmetrical distribution of impurity ions in grain boundary region Sato et al 21,22 electrons captured by traps inside depletion layer and thus accumulated near grain boundary Gupta et al 15 migration process of zinc interstitial (the seminal grain-boundary defect model) Sonder et al 23 high mobility of oxygen ion at high temperature, and flaws like micro-cracks in varistor act as conduits for oxygen Bui et al 24 partial discharges causing the formation of HNO 3 that degrades the Schottky barrier Ramírez et al 25 the lost of oxygen species and β-Bi 2 O 3 phase during degradation process leading to abnormal degradation phenomena and determining its degradation rate, 26 whereas knowledge from atomic scale is quite limited on the role of element that is individually doped and, worse, on the co-doping effect.…”

“…On the contrary, non-monotonic ageing process means that the leakage currents of some grain boundaries could be recovered during the ageing process. 26 A typical monotonic ageing process in I-V characteristic of single grain boundary, measured by micro-contact technique, 26 is shown in FIG. 3(a).…”

“…Such ageing phenomenon of grain boundary is common and expected. Moreover, a typical non-monotonic ageing process in I-V characteristic of individual grain boundary 26 is shown in FIG. 3(b), with its breakdown voltage also around 3 V. Since there is a recovery phenomenon in the pre-breakdown region of I-V curves at early stage of degradation, this ageing process differs obviously from that shown in FIG.…”

“…non-monotonic ageing behavior of DSB 26,28 barrier at early stage of degradation, 28 extended Gupta and Carlson's model 13,48,49 should be inevitably mentioned here, where the role of intergranular phases are taken into consideration additionally. Such extended model centers on the charged particles (FIG.…”

Percolation effects in dc degradation ofZnOvaristors

“…[1][2][3][4][5][6][7] As a mechanism and search of ways to improve the stability of ZnO varistors against degradation are practically important problems. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] The general concepts of a deformation of the grainboundary potential barriers (a decrease in their height and width due to a movement result of dc degradation, the asymmetry of current-voltage characteristics appears. [1][2][3][4][5] The understanding of degradation of some ions in electric field) are the physical basis for the interpretation of this effect.…”