Correlation between the microstructure and electrical properties of Bi–As₂S₃ quasibinar chalcogenides by using AC impedance spectroscopy

The objective of this paper was to study the AC impedance of Bi₅(As₂S₃)₉₅ and Bi₇(As₂S₃)₉₃ chalcogenides in a frequency range of 100 Hz to 1 MHz at different temperatures. A preliminary structural analysis of the compounds by X-ray diffraction technique and scanning electron microscope confirmed the amorphous character for the sample with x = 5 at.% Bi and the existence of two phases (amorphous + crystalline) for the sample with x = 7 at.%. Therefore, the AC impedance analysis by means of an equivalent circuit model was used to establish correlation between the distinct microstructures and electrical properties of these compounds. The presence of the glassy matrix and matrix–crystal interface effects was observed in the sample Bi₇(As₂S₃)₉₃. Moreover, the analysis of impedance data indicated the decrease of resistance with temperature for both samples usually shown by semiconductors i.e. negative temperature coefficient of resistance. The present Bi–As₂S₃ quasibinar chalcogenides also exhibit the temperature dependent relaxation phenomena. According to estimated values of activation energy of relaxation processes, it was concluded that the mechanisms of conductivity and relaxation are the same in both samples.