SnO₂添加のZnOバリスタの課電劣化への影響

抄録

The effects of SnO₂ additon on the electrical degradation characteristics of Bi₂O₃-MnO₂-Co₃O₄-added ZnO varistors were investigated by field-emission scanning electron microscopy (FE-SEM), energy dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD), voltage-current (V-I) characteristics, and capacitance-voltage (C-V) characteristics. The microstructure containing both twins of ZnO and Zn₂SnO₄-type spinel particles was observed at the grain boundary similar to Bi-Mn-Co-Sb₂O₃-added ZnO varistors. Spinel particles began to appear by the addition of SnO₂ over approximately 0.5mol%. Before electrical degradation, value of nonlinearity index α of V-I characteristic for Bi-Mn-Co-SnO₂-added samples was approximately 50 and varistor voltage was 120∼140V/mm. Varistor voltage increased with increasing the amount of SnO₂. Value of α after the electrical degradation showed local maximum at approximately 0.1mol% with the increase of the amount of SnO₂ and then showed local minimum at approximately 0.5mol% similar to the relative integral intensity of XRD diffraction peak for (004) plane at small amount of SnO₂. It is suggested that the diffusion of oxygen ions through the grain boundary is affected by the change of crystal orientation of ZnO grains at the grain boundary by addition of small amount of SnO₂. It is found that the increase of the varistor voltage by addition of SnO₂ is due to the increase of the barrier height of Schottky barriers.