Conductivity in (Ag,Mg)-doped delafossite oxide CuCrO2

Abstract

Undoped and (Ag,Mg)-doped CuCrO2 semiconductor polycrystalline ceramics were produced using the self-combustion urea nitrate process. The effects of the two dopants on the microstructure, optical properties and electrical properties were investigated. X-ray diffraction results showed that all the samples presented a delafossite phase with space group R-3m. Small amounts of CuO and MgCr2O4 secondary phases were found in the doped samples. Scanning electron microscopy images showed the morphology of the crystals, presenting grains with hexagonal platelet like structure. EDS analyses were performed to verify the chemical concentration of elements. The results revealed that for the Mg-doped, the Mg value was close to that expected, while for the (Ag,Mg)-doped samples, Mg and Ag concentrations were much lower than expected. Raman spectroscopy measurements confirmed the presence of Ag and Mg in the structure, but not between the grains. The optical properties of these materials were also investigated using ultraviolet-visible diffuse reflectance, with optical band gaps around 3.3–3.4 eV for pure and (Ag,Mg)-doped ceramics. From XPS experiments, we also observed the formation of the CuCrO2 delafossite phase as well as the substitution of Cr3+ for Mg2+ and Cu+ for Ag+. When compared to undoped samples, those containing (Ag,Mg) exhibited improvements in the electrical properties by a factor of 560.