Nonstoichiometric Zinc Oxide and Indium-Doped Zinc Oxide: Electrical Conductivity and111In-TDPAC Studies

Indium-doped zinc oxide powders have been prepared which show room-temperature electrical conductivities as high as 30 Ω−1cm−1. The indium doping apparently occurs as Zn1−xInxO, Zn1−yInyO1+y/2, or a combination of these. Optimum conductivity occurs for Zn1−xInxO where the maximum value ofxobtained was about 0.5 at%. This substitution results in a lattice volume expansion of 0.4%. The degrees of sample reduction were determined by iodimetric titration. Time differential perturbed angular correlation (TDPAC) spectroscopy on indium doped zinc oxide is consistent with indium substituting at normal zinc sites in the ZnO lattice. TDPAC studies on zinc oxide annealed under zinc vapors show a second environment for the111In probe. In this case, there is an unusually high temperature dependence of the electric field gradient which may be caused by a nearby zinc interstitial. An important conclusion of this work is that zinc interstitials are not ionized and do not therefore contribute significantly to the increased conductivity of reduced zinc oxide.