Microstructure and nonohmic properties of SnO₂–Ta₂O₅–TiO₂ varistor system doped with CuO

Abstract

The microstructure and nonohmic properties of SnO 2 – Ta 2 O 5 – TiO 2 - CuO varistor system were investigated. The proposed samples were doped with different contents of CuO (0–6 mol%) and sintered at 1400°C for 2 h with conventional ceramic processing method. In all the samples, the commonly identified phase was SnO 2 (rutile); however, with increasing doping amount of CuO , the peaks of CuO phase emerged in the X-ray diffraction (XRD) patterns. Scanning electron microscopy (SEM) examination on the fractured surfaces of the samples revealed that a minor amount of CuO dopant can facilitate the sintering of the varistor ceramics, but excessive CuO would mainly segregate at grain-boundaries. The doped CuO may also act as a modifier in the SnO 2 based varistors. The measured electric-field versus current-density characteristics of the samples indicated that both nonlinear exponent and varistor voltage increased with increasing doping amount of CuO up to 3 mol% and then decreased with excessive CuO .