Low‐Temperature Sintering and Electrical Properties of ZnO–Bi ₂ O ₃ –TiO ₂ –Co ₂ O ₃ –MnCO ₃ ‐Based Varistor with Bi ₂ O ₃ –B ₂ O ₃ Frit for Multilayer Chip Varistor Applications

Abstract

The effects of a Bi 2 O 3 –B 2 O 3 frit (denoted as BiBF) on the densification, phase transformation, microstructure, and nonlinear electrical properties of ZnO–Bi 2 O 3 –TiO 2 –Co 2 O 3 –MnCO 3 (ZBTCM)‐based varistors have been investigated. The varistor ceramic with the addition of >2 wt% BiBF can be sintered at 900°C and 96.3% of the theoretical density was achieved. SEM revealed that the microstructure of the varistor ceramics with 2 wt% BiBF is uniform, with an average grain size of 13.5 μm. No porosity is observed. The typical ZnO–Bi 2 O 3 –TiO 2 ‐based varistor phase compositions were detected for all varistor ceramics but the formation of a secondary phase, Bi 4 B 2 O 9 , became apparent when 4 wt% BiBF was added. The Bi 4 B 2 O 9 phase crystallized from the Bi 2 O 3 –B 2 O 3 frit, acting as a potential barrier at the grain boundary, increases the density of interface states N s , barrier height Φ b , and plays an important role in improving the electrical properties of the varistor ceramics. However, a large amount will be detrimental. Optimum properties were exhibited for the varistor ceramics with 2 wt% BiBF sintered at 900°C, with E 1 mA =124.9 V/mm, α=46.2, and J L =0.2 μA/cm 2 . The reactivity of the varistor ceramic with Ag was also studied. The excellent electrical properties and low sintering temperature, coupled with chemical compatibility with Ag, suggest that Bi 2 O 3 –B 2 O 3 frit sintering aids for ZnO–Bi 2 O 3 –TiO 2 –Co 2 O 3 –MnCO 3 (ZBTCM)‐based varistors have great potential for using the base metal Ag as inner electrodes for low‐voltage MLV fabrication.