Sol–gel synthesis and characterization of the delafossite CuAlO2

Abstract : Nanocrystalline CuAlO2 is synthesized by sol–gel method using ethylene glycol as solvent. The stages of formation are followed by thermal analysis. The X-ray diffraction pattern of the powder heat-treated at 1100 °C shows a single phase, indexed in a rhombohedral symmetry (R 3¯¯¯ m). The apparent crystallite size (57 ± 8 nm) is determined from the Williamson–Hall plot. The direct optical transition (=3.69 eV), evaluated from the diffuse reflectance spectrum, is attributed to the charge transfer (O2−: 2p → Cu+: 4s). The oxide is p-type semiconductor, and the conduction occurs predominantly by small polaron hopping between mixed valences Cu2+/+, due to oxygen insertion in the layered crystal. The photoelectrochemical characterization gives a flat band of 0.20 VSCE and a hole density of 1.13 × 1018 cm−3. The semicircle centered on the real axis, in the electrochemical impedance spectroscopy (EIS), is due to the absence of constant phase element with a pure capacitive behavior. The straight line at 35° at low frequencies is attributed to the diffusion in the layered structure.
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Nadia Benreguia, Antoine Barnabé, Mohamed Trari. Sol–gel synthesis and characterization of the delafossite CuAlO2. Journal of Sol-Gel Science and Technology, Springer Verlag, 2015, 75 (3), pp.670-679. ⟨10.1007/s10971-015-3737-x⟩. ⟨hal-02094885⟩

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