Investigation of the Effects of CaO Doping on the Microstructure and Electrical Properties of ZnO-Based Linear Resistance Ceramics

ZnO-Al2O3-MgO-SiO2-TiO2-CaO (ZnO-based) linear resistance ceramics were prepared by the conventional ceramics method with different amounts of CaO. The impact of CaO doping on the phase composition, microstructures and electrical properties of ZnO-based linear resistance ceramics was investigated in detail. The research showed that CaO doping not only limits the growth of ZnAl2O4 and ZnO grains—in particular, the grain size of ZnAl2O4 decreased from 4.40 μm to 1.38 μm—but also improves the electrical properties. The grain boundary barrier height and nonlinear coefficient decreased with the increase in CaO content, and the resistance temperature coefficient increased from −5.65 × 10−3/°C to 1.04 × 10−3/°C. The 4.00 mol.% CaO-doped ZnO-based linear resistance ceramics were found to possess excellent electrical properties: the resistivity is 44.87 Ω cm, the grain boundary barrier height is 0.011 eV, the nonlinear coefficient is 1.05 and the resistance temperature coefficient is −0.822 × 10−3/°C, a stable resistivity against frequency.