Effects of AgNO₃ doping on the microstructure and the electrical properties of ZnO-based linear resistors

ZnO–Al₂O₃–MgO–La₂O₃–SiO₂ system linear resistors were doped with various doping content of AgNO₃ (0, 0.1, 0.2, 0.3, 0.4, and 0.5 mol%) for improving the electrical properties. All samples were synthesized at 1340 °C for 3 h using a solid-state sintering in the air ambient. The microstructure and crystal characterizations of the samples were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The results of XRD indicate that the main phase of all samples was hexagonal wurtzite structure of ZnO. Also, LaAlO₃ and ZnAl₂O₄ compounds are found formed in all experimental samples. From the SEM images, it can be seen that the average grain size of all doped samples increased compared to the undoped sample. This illustrated that doping of AgNO₃ could promote the growth of ZnO grains. The dielectric and electrical properties of all samples were tested and analyzed. The results show that the resistivity of all doped samples increase with the increase of AgNO₃ doping content, and the grain boundary barrier height decreased for all doped samples. When the doping content is 0.1 mol%, the ZnO linear resistor exhibits excellent performance with grain boundary barrier height (φ₀) of 0.0345 eV, nonlinear coefficient (α) of 1.01, and resistance temperature coefficient (α_T) of − 2.07 × 10^–3/°C.