Mechanism of Ga2O3 addition on the enhancement of electrical and mechanical properties of ZnO based varistor

ZnO based varistors added with minor content of Bi 2 O 3 , Sb 2 O 3 , Co 2 O 3 , SiO 2 , MnO 2 et al. with high voltage gradient, excellent mechanical and thermal properties were fabricated by Ga 2 O 3 doping and using raw ZnO nanoparticles . The compositions and microstructure of the varistors, as well as their electrical, mechanical, and thermal properties were investigated via XRD , XPS, SEM, E-J, C–V, mechanical, and thermal expansion measurements. Also, the mechanism of Ga 2 O 3 addition on the electrical and mechanical properties of the varistors was discussed in detail. Results showed that the added Ga 2 O 3 preferentially occupied the lattice position of ZnO crystal through the formation of a substitutional solid solution (Donor doping), it then occupied the void position through the formation of an interstitial solid solution (Acceptor doping), in which the residual Ga 2 O 3 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 Ga 2 O 3 content was 0.40 mol%, values of E 1mA , α, and K were 1235.00 V mm −1 , 46.0, and 1.37, respectively, being due to the small particle size and the related 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 σ f , E f , and K IC could reach 147.43 MPa, 213.61 GPa and 2.05 MPa m 1/2 , showing improvements of 25.29%, 47.67%, and 38.51%, respectively, compared with those of ZnO based varistors without Ga 2 O 3 .