Ag₃Ge₂S₅Br: Synthesis, structure and ionic conductivity

Chem. Met. Alloys 7 (2014) 139-148

https://doi.org/10.30970/cma7.0305

Mykola Moroz, Pavlo Demchenko, Vitaliy Romaka, Roman Serkiz, Lev Akselrud, Roman Gladyshevskii, Oleksiy Mykolaychuk

A new compound, Ag₃Ge₂S₅Br, was found on the intersection of the Ag₃SBr–GeS₂ and Ag₂Ge₂S₅–AgBr polythermal cross-sections of the Ag₂S–GeS₂–AgBr system. The peritectic process L + GeS₂ « Ag₃Ge₂S₅Br takes place at T = 727 K. The crystal structure of Ag₃Ge₂S₅Br was solved and refined using X-ray powder diffraction data: own structure type, space group P2₁3 – b²a⁵, Pearson symbol cP44, Z = 4, a = 10.16702(7) Å, R_I = 0.0395, c² = 3.19. Ag₃Ge₂S₅Br was also obtained in the glassy state. The charge and mass transfer of the crystalline and glassy phases was investigated by the dc probe method between 250 and 495 K. The samples are purely ionic (Ag⁺, Br^–) conductors. The influence of lining of the transport channels by the halogens (Br^–, I^–) on the conductivity of crystalline (Ag₃Ge₂S₅Br + 10 wt.% GeS₂) and glassy (Ag₃Ge₂S₅Br) samples was studied. Electronic structure calculations (FP-LAPW method) support the experimental results.

Isosurface (ρ = 0.4 e/ų) of the electron density in one unit cell of Ag₃Ge₂S₅Br

Keywords

Ag–Ge–S–Br / Phase formation / Crystal structure / Electrical conductivity / Superionics / DFT calculations