Surface analysis and electrical property of oxygen- and Ga-doped CuAlO2

We have investigated the physicochemical properties of the p-type delafossite conductors, CuAlO2, and the possibility of charge carrier enriching to the delafossite. The oxygen partial pressure was a critical condition to get the stoichiometric CuAlO2 during the synthesis process, Po2 = 0.175 atm at 1313 K. A series of CuAl1−xGaxO2 (0 ≤ x ≤ 0.05) were prepared to study the impurity effect of Ga3+ in the delafossite. The Cu2+ ion created in the delafossite by the homovalent substitution—Al3+ (67.5 pm in diameter) could be replaced by Ga3+ (76.0 pm in diameter) up to x = 0.03 in CuAl1−xGaxO2. The different charge densities (+ ion charge/radius of ion) between the 3 + ions might be the reason for the formation of Cu2+in the Ga-doped CuAlO2. But the distinctive conductivity enhancement by the Ga doping was not observed. The other type of p-doping, inserting excess oxygen into the lattice (CuAlO2+x), was observed near the sample's surface due to the low diffusion rate of the oxygen in the delafossite lattice.