The effect of SiO₂on electrical properties of low‐temperature‐sintered ZnO–Bi₂O₃–TiO₂–Co₂O₃–MnO₂‐based ceramics

Abstract

ZnO–Bi2O3–TiO2–Co2O3–MnO2‐based (ZBTCM) varistors were fabricated via the conventional solid‐state method, and the effect of SiO2 content on the phase transformation, microstructure, and electrical properties of the ZBTCM had been investigated. Results showed that this varistor can be sintered at a low temperature of 880°C with a high sintering density above 0.95 of the ZnO theoretical density. In these components, SiO2 acts as a controller in ZnO grain growth, decreasing the grain size of ZnO from 3.67 to 1.92 μm, which in turn results in an increase in breakdown voltage E1mA from 358.11 to 1080 V/mm. On the other hand, SiO2 has a significant influence on the defect structure and component distribution at grain‐boundary regions. When SiO2 content increases from 0 to 4 wt%, the value of the interface state density (Ns) increases sharply. At the same time, the electrical properties are improved gradually, and reach an optimized value with the nonlinear coefficient (α) up to 54.18, the barrier height (ϕb) up to 2.90 eV, and the leakage current (IL) down to 0.193 μA/cm2.

Research method and mechanism analysis of a novel high-performance quaternary Zn–Sr–Co–Sb varistor ceramic

“…However, Co 3+ with a smaller ion radius (0.55 Å) than Zn 2+ (0.74 Å) may easily enter deep into the core of the ZnO grain, 24,26 which is in accordance with EDS. This does not provide the above reactions to improve φ B at the grain boundary layer.…”

“…The N s and N d of the ternary system increase to 0.64 Â 10 17 m À2 and 2.13 Â 10 24 m À3 , resulting in an increase in j B up to 2.04. However, Co 3+ with a smaller ion radius (0.55 Å) than Zn 2+ (0.74 Å) may easily enter deep into the core of the ZnO grain, 24,26 which is in accordance with EDS. This does not provide the above reactions to improve j B at the grain boundary layer.…”

“…The barrier height φ B is enhanced from 0.88 to 2.04 by Co doping. Co improves φ B by the following solid-solution reaction at the grain boundary as follows: 24,26,46 The N s and N d of the ternary system increase to 0.64 × 10 17 m −2 and 2.13 × 10 24 m −3 , resulting in an increase in φ B up to 2.04.…”

“…Besides, the above points suggest that the grain boundary acts as a ''carrier'' of adsorbed oxygen and negatively charged defects. 24,26,28 It is deduced that the electron at the surface of the ZnO grain is prone to be captured by the positive charge inside the ZnO grain when no grain boundary is built between the ZnO grains. In a word, SrZnO 2 acts as a grain boundary ''skeleton'' to induce j B , which is similar to Bi 2 O 3 .…”

“…The barrier height j B is enhanced from 0.88 to 2.04 by Co doping. Co improves j B by the following solid-solution reaction at the grain boundary as follows: 24,26,46…”