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Single crystals of ternary argyrodites Ag 7 PS 6 and Ag 8 GeS 6 were grown by the method of directional crystallization from the melt. Large samples with size l = 30 - 40 mm and d = 12 mm were obtained. Grown crystals were investigated by powder XRD, DTA, SEM and EIS methods. The crystal structure of the electron-ionic conductor Ag 7 PS 6 was studied by the Rietveld method. The low-temperature modification of Ag 7 PS 6 crystallizes in a primitive cubic cell SG P2 1 3 (No 198) with lattice parameters a = 10.3917 Å and Z = 4. It was established by the SEM method that the studied ternary sulfides Ag 7 PS 6 and Ag 8 GeS 6 are characterized by a defect microstructure. The frequency (1 × 101 – 3 × 105 Hz) and temperature (293–383 K) behavior of electrical conductivity of single crystalline samples were studied. Using the EEC, the contributions of ionic and electronic conductivity were determined and the corresponding activation energies for Ag 7 PS 6 and Ag 8 GeS 6 single crystals were calculated. The influence of structural parameters of Ag 7 PS 6 and Ag 8 GeS 6 on electrical parameters of single crystals is established. [Display omitted] • Single crystal growth of halogen-free argyrodites Ag 7 PS 6 and Ag 8 GeS 6 was performed. • Crystal structure of LT-Ag 8 GeS 6 was refined and for LT-Ag 7 PS 6 – established. • Ag 7 PS 6 and Ag 8 GeS 6 are mixed conductors with low values of ionic conductivity. • Activation energy for ionic and electronic conductivity was established. • Parameters of ionic conductivity is discussed considering structural descriptors. [ABSTRACT FROM AUTHOR]

This paper presents the preparation and study of new ceramics of Ag+-conductive solid electrolytes. Ceramic disks of Ag 6+x (P 1-x Ge x)S 5 I (х = 0; 0.25; 0.5; 0.75) solid solutions were obtained in two stages: cold pressing to a relative density of 91 ± 1% and annealing at 923 K. The prepared Ag 6+x (P 1-x Ge x)S 5 I ceramics were investigated by SEM, EDS, impedance spectroscopy and microhardness measurement. Ceramic materials are phase homogeneous, and the average size of crystallites in annealed ceramic materials stays in the range of ∼3.1–4.7 μm, and the porosity is 6–8%. Ag 6+x (P 1-x Ge x)S 5 I ceramics belong to ion-electron conductors with a significant predominance of ionic conductivity. The compositional dependence of ionic conductivity and its activation energy isn't monotonous. The highest values of ionic conductivity 4.8 × 10−2 S/cm (298 K) are obtained for the Ag 6.75 (P 0.25 Ge 0.75)S 5 I, and the minimum activation energy 0.093 eV for Ag 6.5 P 0.5 Ge 0.5 S 5 I composition. The influence of microstructure and recrystallization process on electrical parameters of Ag 6+x (P 1-x Ge x)S 5 I ceramics is discussed. [Display omitted] • Ceramic material of Ag 6+x (P 1-x Ge x)S 5 I solid solutions were prepared by cold pressing from the microcrystalline powders. • Prepared Ag 6+x (P 1-x Ge x)S 5 I ceramics were investigated by SEM, EDS, EIS and microhardness measurements. • Ceramics demonstrate high ionic conductivity with a maximum for Ag 6.75 (P 0.25 Ge 0.75)S 5 I (4.8 × 10−2 S/cm) composition. • Activation energy values for all Ag 6+x (P 1-x Ge x)S 5 I ceramics are lower than for the initial compounds. [ABSTRACT FROM AUTHOR]