Physical properties of CuAlO2 single crystal

CuAlO2 single crystal elaborated by the flux method is a narrow band gap semiconductor crystallizing in the delafossite structure (SG R3¯m). Oxygen insertion in the layered lattice generates p-type conductivity where most holes are trapped in surface-polaron states. The detailed photoelectrochemical characterization and electrochemical impedance spectroscopy (EIS) have been reported for the first time on the single crystal. The study is confined in the basal plan and reversible oxygen insertion is evidenced from the intensity potential characteristics. The oxide is characterized by an excellent chemical stability; the semi-logarithmic plot gave a corrosion potential of−0.82 VSCE and an exchange current density of 0.022 μA cm−2 in KCl (0.5 M) electrolyte. The capacitance measurement (C−2–V) shows a linear behavior from which a flat band potential of +0.42 VSCE and a doping density NA of 1016 cm−3 have been determined. The valence band, located at 5.24 eV (0.51 VSCE) below vacuum, is made up of Cu-3d orbital. The Nyquist plot exhibits a pseudo-semicircle whose center is localized below the real axis with an angle of 20°. This can be attributed to a single relaxation time of the electrical equivalent circuit and a constant phase element (CPE). The absence of straight line indicates that the process is under kinetic control.