Synchronously Improved Voltage Gradient and Mechanical Properties of ZnO Based Varistor by Doping Ga2O3

ZnO based varistors with high voltage gradient and excellent mechanical and thermal properties were fabricated by Ga2O3 doping and using nanoparticles. The compositions and microstructure of the varistors, as well as their electrical, mechanical and thermal properties were investigated by XRD, XPS, SEM, E-J, C-V, mechanical and thermal expansion measurements. Also, the mechanism of Ga2O3 addition on electrical and mechanical properties of the varistors was discussed detailedly. Results showed that the added Ga2O3 preferentially occupied the lattice position of ZnO crystal through the formation of a substitutional solid solution (Donor doping), they then occupied the void position through the formation of an interstitial solid solution (Acceptor doping), in which residual Ga2O3 existed in the grain boundary and served as inversion boundaries. The formation of the substitutional and interstitial solid solutions helped to improve the electrical properties, when the Ga2O3 content was 0.40 mol%, E1mA, α and K were 1235.00 V·mm− 1, 46.0 and 1.37, respectively, being due to the small particle size and the relative content of donor, acceptor and grain boundary in ZnO grain; The increased content of inversion boundaries stimulated the abnormal growth of ZnO grain, and the formed plate-like grain helped to improve the mechanical properties and thermal expansion coefficient of the varistors, values of σf, Ef, and KIC reached 147.43 MPa, 213.61 GPa and 2.05 MPa·m1/2, showing improvements of 25.29%, 47.67%, and 38.51%, respectively, compared with those of ZnO varistors without Ga2O3.