Relation between Grain Boundary and Electrical Degradation of ZnO Varistors

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

“…In contrast, it has been reported that the crystal structure of Bi 2 O 3 at grain boundaries changes to the α, γ, or δ-type structure owning to the composition of impurities added or the sintering and annealing conditions. [8][9][10]16,[19][20][21] However, in this study, it was found that the degree of electrical degradation is related to other factors in Fig. 8.…”

“…Furthermore, it has been reported that the electrical degradation characteristics of samples with 0.1 mol% Sb 2 O 3 or less is correlated to the orientation of ZnO grains; this is because the mobility of oxide ions or Zn 2+ ions depends on the orientation of ZnO grains. 9,10 Fig. 4 shows the relative integral intensity of the diffraction peak for the (0 0 4) plane of ZnO grains of Sb 2 O 3 -added samples before and after annealing.…”

“…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. 9,10 In previous studies, the effect of annealing on electrical degradation characteristics of ZnO varistors has been reported.…”

“…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. 9,10 In previous studies, the effect of annealing on electrical degradation characteristics of ZnO varistors has been reported. 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.…”

Effect of SnO₂ Addition on Electrical Degradation Characteristics of ZnO Varistors

“…Relative integral intensity of (004) plane 2.0 The mechanism of the non-ohmic property of ZnO visitors has been explained using energy-band model of double Schottky barriers formed at grain boundaries of ZnO grains. Moreover, it is reported that one of the mechanism of the electrical degradation is due to the diffusion of oxygen ions through the grain boundary caused by application of bias voltage and then double Schottky barriers are distorted by the re-distribution of electrons and holes near the grain boundary (1) (2) . It is known that ZnO varistors with containing of Sb 2 O 3 obtained excellent properties, such as high varistor voltage, improvement of the uniformity of the grain size and improvement of the electrical degradation characteristics (2) .…”