Grain boundary structures in zinc oxide varistors

Lattice misorientations across electrically active interfaces in antimony and bismuth doped zinc oxide varistors have been determined by electron backscattered pattern analysis and coupled with the orientations of the associated grain boundary planes established by depth resolved electron beam induced current (EBIC) in order to index the crystal faces forming either side of the grain boundary plane. When correlated with the EBIC contrast observed at the grain boundary, it was found that a symmetrical EBIC profile was only found at interfaces where both crystal faces forming the grain boundary were oriented at a similar angle from the polar basal plane orientation. At the majority of grain boundaries the structure was such that one face lay close to the basal plane orientation with the other face much further away. In these cases the EBIC was suppressed on the side of the grain boundary whose face lay close to the basal orientation. The implications of these observations on the electrical structure of the interface and microstructural development are discussed.