Positron annihilation spectroscopy was performed in a Doppler mode to characterize the negatively charged grain‐boundary defect, V′Zn, in ZnO varistor. The positron annihilation spectroscopy study was conducted as a function of annealing treatment. As the annealing temperature increases from 400 to 600C the concentration of VZn increased, at intermediate temperatures from 600 to 800C the V′Zn concentration decreases, and finally, beyond 800C it increased again. These results were explained in terms of an earlier grain‐boundary defect model (Gupta & Carlson, 1987). The effect of quenching upon the positron annihilation spectroscopy response was also explained in terms of a defect model.

Grain‐Boundary Characterization of ZnO Varistors by Positron Annihilation Spectroscopy. Gupta, T.K., Straub, W.D., Ramanachalam, M.S., Schaffer, J.P., Rohatgi, A.: Journal of Applied Physics, 1989, 66[12], 6132