Study on Recovery of Electrical Degradation of ZnO Varistors

Abstract:

The relationship between the crystal structure of Bi2O3 and the recovery of the electrical degradation of ZnO varistors was investigated. The evaluation methods used were analysis of the voltage-current (V-I) characteristics, scanning electron microscopy (SEM), energy-dispersion X-ray spectroscopy (EDX), and X-ray diffraction (XRD) measurements. The electrical degradation was estimated by the nonlinearity of the V-I characteristics. A marked recovery of the nonlinearity of the V-I characteristics was observed for a sample having the crystal structure of δ-type Bi2O3. It is speculated that the electrical degradation is markedly recovered for optimum conditions of both the amount and the crystal structure of the added Bi2O3, because, for samples sintered for a long time, the recovery speed is shorter than that for samples sintered for a shorter time. During long-time sintering, the amount of Bi2O3 decreased because of evaporation. No change of the crystal structure of Bi2O3 was observed upon repeated the electrical degradation and the recovery. It is suggested that another mechanism apart from the diffusion of oxygen ions through the grain boundaries of ZnO particles contributes to the electrical degradation and recovery of the nonlinearity of V-I characteristics.

• Periodical: Key Engineering Materials (Volume 350)
• Pages: 209-212
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.350.209
• Online since: October 2007
• Authors: Hiroshi Yoshida, Masayuki Takada, Shinzo Yoshikado
• Keywords: Crystal Structure of Bi₂O₃, Recovery of Electrical Degradation, Thermal Annealing, ZnO Varistor

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[35] [30] [25] [20] [15] [10] [5] α 987654321 Degradation cycle before degradation after degradation after recovery Fig. 6 Values of α for the repetition of the electrical degradation and the recovery for Bi-Mn-Co(1. 8mol%)-added sample sintered for 4. 5h.

[3] [4] [5] [6] 102.

[3] [4] Voltage [V] 10-6 10-5 10-4 10-3 10-2 Current density [A/cm.

[2] ] Co: 1. 8mol% sintered for 3 h before anealing after anealing (a) Sintered for 3h.

[4] [6] [12] [4] [6] 102.

[4] Voltage [V].

[10] -6.

[10] -5.

[10] -4 10-3.

[10] -2 Current density [A/cm.

[2] ] Co: 1. 8mol% sintered for 4. 5 h before anealing after anealing (b) Sintered for 4. 5h Fig. 7 V-I characteristics for Bi-Mn-Co(1. 8mol%)-added sample. (a) sintered for 3h，(b) sintered for 4. 5h.