Electrical and structural characteristics of non-stoichiometric Cu-based delafossites

Non-stoichiometric CuxGaO2 polycrystalline ceramics were prepared using solid-state synthesis methods and their structural and electrical properties were characterized as a function of x. While single phase delafossite could only be confirmed for the stoichiometric composition, X-ray diffraction results show that the a and c lattice parameters were stable from Cu0.98GaO2 to Cu1.02GaO2. Below x = 0.97, the structure underwent a 0.4% decrease in cell volume. For compositions rich in Cu, the a parameter remained constant while the c parameter shrank at a constant rate. Despite these changes in cell dimensions, the results of current-voltage and impedance spectroscopy measurements indicate that both the conductivity and the activation energy do not vary with x. The absence of a change in electrical properties as well as the formation of secondary phases in non-stoichiometric compositions suggests that CuGaO2 does not allow significant deviations from the ideal CuGaO2 stoichiometry. This implies that the p-type conductivity is fixed by a defect species that does not vary with the Cu stoichiometry.