Copper substitutions in synthetic miargyrite α-AgSbS2 mineral: Synthesis, characterization and dielectrical properties

• Ag0.8Cu0.2SbS2 and Ag0.7Cu0.3SbS2 are isostructural with the natural miargyrite α-AgSbS2 mineral.
• The overall resistance correspond to grain boundary and electrode/sample interface responses.
• In these solid solutions no ferroelectric-like transition is noticed.
• The overall frequency dependence follows the Jonscher's universal power law.
• σac vs. frequency can be normalized by Summerfield scaling procedure.

The nominal compositions Ag0.8Cu0.2SbS2 and Ag0.7Cu0.3SbS2 have been synthesized by conventional ceramic solid-state reaction at high temperature. X-ray diffraction (XRD) and scanning electron microscopy chemical analysis (SEM-EDAX) revealed single phases, isostructural to the natural miargyrite α-AgSbS2 mineral. Examination of the lattice parameters shows a decrease in the cell volume with increasing copper substitutions. The Raman analysis displays absorptions which may be assigned to the Sb–S stretching vibrations of the SbS3 pyramids. The impedance-frequency analysis showed grain boundary and electrode interface contributions in non-Debye type relaxation, following Jonscher's universal power law. The giant permittivity response is attributed to extrinsic effects without evidence of a ferroelectric transition. Summerfield scaling, leading to the superposition of impedance analysis, implies that the relaxation is thermally activated, without introducing more than one underlying transport mechanism.