Impedance response and I–V characteristics of Bi6(As2S3)94 and Bi7(As2S3)93 at elevated temperature

We report on the dynamics of the softening process of Bi₆(As₂S₃)₉₄ through studying the AC impedance response in the frequency interval of 1 Hz to 10 MHz at operating temperatures of 323–373 K. The increase of glass fictive temperature with heating rate, observed in DSC curves, is explained using the Lasocka equation. The analysis of impedance spectra indicated single-phase glass behavior for Bi₆(As₂S₃)₉₄, whereas the appearance of internal interfaces was confirmed for Bi₇(As₂S₃)₉₃ at all temperatures. While this was previously assigned to the boundary surface of the matrix–interface region and the crystalline centers themselves, the extension of the observed range now revealed that at low temperatures, amorphous phase separation without crystal precipitation comes into play. By analyzing the impedance data, we determined refined DC resistance and relaxation time values, and also confirmed the decrease of resistance with temperature for both compositions. Similar activation barriers for α relaxation and charge carrier mobility indicate that both processes are strongly coupled. The I–V characteristics of the Bi₇(As₂S₃)₉₃ sample recorded up to T = 373 K show bipolar resistive switching behavior controlled by voltage. At higher temperatures, there is switching with conducting filament due to the contribution of crystalline centers.