Microstructure and electrical properties of Sm2O3 doped Bi2O3-based ZnO varistor ceramics

Abstract

Abstract The dependence of the bulk density, microstructure and dc electrical properties of bismuth oxide (Bi 2 O 3 )-based zinc oxide (ZnO) varistor ceramics for various samarium oxide (Sm 2 O 3 ) contents was investigated. The value of bulk density was found to 5.43–5.50 g cm −3 with Sm 2 O 3 (mol%) content. The maximum value of bulk density is observed to be 5.50 for 0.30 mol% Sm 2 O 3 containing varistor ceramics. The grain sizes for all the samples calculated from the scanning electron micrographs were found to decrease as Sm 2 O 3 increases. The presence of ZnO phases, Bi-rich phases, spinel phases and Sm 2 O 3 phases were observed in the samples by the energy dispersive X-ray analysis and X-ray diffraction analysis. As the Sm 2 O 3 amount increased in the Bi 2 O 3 -based ZnO varistor ceramics, the nonlinear coefficient, α increased up to 0.10 mol%, reaching a maximum value of 58 and then decreased. The breakdown electric field, E b , increased with the increase of Sm 2 O 3 content with a maximum value of 3220 V cm −1 for the 0.75 mol% Sm 2 O 3 doped ZnO varistor ceramics. The leakage current, I L , showed a minimum value of 1.10 μA for the composition of 0.30 mol% Sm 2 O 3 doped Bi 2 O 3 -based ZnO varistor ceramics. The 0.30 mol% Sm 2 O 3 -doped Bi 2 O 3 -based ZnO varistor ceramics sintered at 1200 °C exhibited a good stability for dc accelerated aging stress of 0.90 V 1 mA /90 °C/12 h.