Tweaks to intrinsic point defects in ZnO ceramics via MnCO3 and their effect on electrical properties

Abstract

Transition metal elements are necessary dopants in ZnO ceramics to improve electrical properties by defects engineering. In the present study, the tweaking effect of MnCO3 on the intrinsic point defects, i.e., the zinc interstitial and the oxygen vacancy, are investigated to optimize electrical properties of ZnO ceramics. After analyzing microstructure and dielectric response, it was found that Mn2+ was further oxidized to Mn4+ during sintering and Mn4+ solved into ZnO grains and inhibited the formation of the intrinsic point defects. On the other hand, due to the increase of the interface states contributed by Mn separation at grain boundaries, the barrier width broadened to keep charge neutrality. As a result, although the barrier height decreased from 0.68 eV to 0.54 eV as MnCO3 content increased from 0 mol% to 0.63 mol%, the nonlinear electrical properties were enhanced, that is, the breakdown field increased from 188.47 V/mm to 234.82 V/mm, the nonlinear coefficient increased from 12.87 to 74.76, and the leakage current density decreased from 22.08 μA/cm2 to 0.04 μA/cm2. Combined with the stability during DC aging tests, it is suggested that the optimal content of MnCO3 is 0.38 mol%. The study also indicates that the barrier width is a sensitive parameter in optimizing electrical properties of ZnO ceramics, instead of the sole focus on higher barrier height.