The compound Cu(In 0.6 Ga 0.4 ) 3 Se 5 prepared by fusion in sealed tube is a wide band gap semicon ductor; it crystallizes in the P chalcopyrite structure with a direct transition of 1.42 eV. Its transport properties exhibit a semi conducting behavior, which seem to be not intrinsic but rather attributed to selenium vacan cies, and the conductivity is well described by small polaron hopping: σ = σ 0 exp{-29/kT}(Ohm cm) -1 with an effective mass of ~2m 0 . The thermo power is negative and changes little with temperature, suggesting that the conduction mechanism is mostly due to electron hopping. The analyzed material shows a chemical sta bility over a broad pH range; the semi logarithmic plot in KOH solution displays an exchange current density of 27 μA cm -2 and a corrosion potential of -0.204 V SCE . The capacitance measurement (C -2 -V) exhibits a linear behavior, characteristic of n type conductivity, from which a flat band potential of -0.530 V SCE and an electron density of 3.49 × 10 20 cm -3 are determined. The Nyquist plot shows a semicircle due to the predom inance of the bulk contribution (=127 Ohm cm 2 ) and a low density of surface states. The centre is localized below the real axis with a depression angle of 12° ascribed to a constant phase element (CPE). The straight line in the low frequencies region is due to the Warburg diffusion.
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