Single or multiple electrically active grain boundaries were isolated in polycrystalline pellets by using an in-diffusion method. The breakdown voltage and non-linearity coefficient of Pr-Co, Pr-Mn, Pr-Ni and Pr-Mn-Co doped specimens were examined as a function of the processing conditions. Zero-bias deep-level transient spectroscopic measurements revealed the existence of 2 deep levels, in each type of specimen, having characteristic energy levels of 0.25, 0.37 and 0.60eV; depending upon the dopant type.

Electrically Active ZnO Boundaries. Baek, K.K., Broniatowski, A., Tuller, H.L.: Materials Science Forum, 1993, 126-128, 737-40