Studies on structural and electrical properties of copper-doped zinc oxide powders prepared by a solid state method at high temperatures

The synthesis, crystal structure and electrical conductivity properties of Cu-doped ZnO powders (in the range of 0.25-15 mole %) is reported. I-phase samples, which were indexed as single phase with a hexagonal (wurtzite) structure in the Cu-doped ZnO binary system, were determined by X-ray diffraction. The limit solubility of Cu in the ZnO lattice at this temperature is 5 mole % at 1000 degrees C. The impurity phase was determined as CuO when compared with standard XRD data using the PDF program. We focused on single I-phase ZnO samples which synthesised at 1000 degrees C because the limit solubility range is widest at this temperature. It was observed that the lattice parameters a increased and c decreased with Cu doping concentration. The morphology of the I-phase samples was analysed with a scanning electron microscope. The electrical conductivity of the pure ZnO and single I-phase samples were studied using the four-probe dc method at temperatures between 100 and 950 degrees C in an air atmosphere. The electrical conductivity values of pure ZnO and 5 mole % Cu-doped ZnO samples at 100 degrees C were 2 x 10(-6) and 1.4 x 10(-4) ohm(-1) cm(-1), and at 950 degrees C they were 1.8 and 3.4 ohm(-1) cm, respectively. In other words, the electrical conductivity slightly increased with Cu doping concentration. Also, it was observed that the activation energy of the I-phase samples was decreased with Cu doping concentration.