Physical and photoelectrochemical properties of spherical nanoparticles of α-AgBiS 2
Résumé
We have investigated the physical and photo electrochemical properties of α-AgBiS2 (schapbachite), synthesized from Bi2S3 and Ag2S in evacuated Pyrex ampoule at 550 °C. The precursors are prepared by precipitation from nitrates in ethylene glycol using thiourea as complexing agent and sulfide source. AgBiS2 crystallizes in a rock salt structure (Fm-3m). The transmission electron micrograph shows spherical nanoparticles with an average size of ~ 30 nm, a value very close to that obtained from the Williamson-Hall plot of the XRD powder pattern (33.06±1.28 nm). HRTEM gives inter reticular distance of 0.33 nm, a value in excellent agreement with that of the SAED analysis (d111=0.3276 nm). The diffuse reflectance spectrum indicates a direct optical transition of 0.89 eV. The thermal variation of the electrical conductivity is characteristic of semiconducting behavior with activation energy of 0.20 eV, electron mobility (µ300K) of 2.43 × 10−4 cm2 V−1 s−1 and an effective mass of 2.88 mo. The intensity-potential J(V) curve in alkaline medium (pH 10.2) shows a good electrochemical stability. The dark capacitance (C−2-V) exhibits a linear behavior, characteristic of n-type conduction (dC−2/dE>0), from which a flat band potential of 0.33 VSCE and an electrons density of 2.57 × 1021 cm−3 are determined. The valence band derives from S2−: 3p states while the conduction band is made up mainly of Ag+: 5 s orbital. The electrochemical impedance spectroscopy (EIS), measured in the dark and under illumination over the frequency range (10−3−105 Hz), indicates the contribution of both the bulk and grain boundaries.
Graphical abstract