Continuous Existence of Bismuth at Grain Boundaries of Zinc Oxide Varistor without Intergranular Phase

The state of Bi at the grain boundaries of ZnO varistors was analyzed using FE‐TEM with EDS point and mapping analysis with a spatial resolution of less than 1 nm. The continuous existence of Bi of less than 1/2 atomic layer has been confirmed at ZnO‐ZnO junctions without any secondary phase. The coexistence of a crystalline Bi 2 O 3 and an amorphous phase has been found, and a new model has been proposed for the transition of the Bi‐O phase from crystalline Bi 2 O 3 to atomic Bi via an amorphous phase with decreasing thickness of grain boundary phases.