Phase relations along the Ag8GeS6–[(AgBr)4·GeS2] cross-section. Crystal structure and electric conductivity of Ag6GeS4Br2 in bulk

In the search for fast lithium-ion conducting solids for the development of safe rechargeable all-solid-state batteries with high energy density, thiophosphates and related compounds have been demonstrated to be particularly promising both because of their record ionic conductivities and their typically low charge transfer resistances. In this work we explore a wide range of known and predicted thiophosphates with a particular focus on the cubic argyrodite phase with a robust three-dimensional network of ion migration pathways. Structural and hydrolysis stability are calculated employing density functional method in combination with a generally applicable method of predicting the relevant critical reaction. The activation energy for ion migration in these argyrodites is then calculated using the empirical bond valence pathway method developed in our group, while bandgaps of selected argyrodites are calculated as a basis for assessing the electrochemical window. Findings for the lithium compounds are also compared to those of previously known copper argyrodites and hypothetical sodium argyrodites. Therefrom, guidelines for experimental work are derived to yield phases with the optimum balance between chemical stability and ionic conductivity in the search for practical lithium and sodium solid electrolyte materials.

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Photoluminescence and electronic structure of α'-Ag8GeS6 crystals

Semkiv,

Kashuba,

Ilchuk

et al. 2023

Low Temperature Physics

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The Ag8GeS6 crystal was synthesized by the direct melting of the elementary Ag, Ge, and S high-purity grade stoichiometric mixture in a sealed quartz ampoule. This argyrodite crystallizes in orthorhombic structure [Pna21 space group (No. 33)] below ≈483 K. The theoretical first-principle calculations of the electronic band structure and density of states of an α'-Ag8GeS6 crystal are estimated by the generalized gradient approximation. The Perdew–Burke–Ernzerhof functional was utilized. All of the calculated parameters correlate well with the known experimental data. Based on the electronic band structure, the effective mass of the electrons and holes was calculated. The anisotropic behavior of electronic band structure is discussed. Temperature and carrier concentration dependence of the Seebeck coefficient is calculated. The temperature behavior of α'-Ag8GeS6 photoluminescence spectra is presented. The emission spectra are studied in the temperature range between 17 and 130 K and laser power excitation between 4 and 512 mW and in the spectral range of 750–1650 nm. Two main emission bands at ≈1.35 and ≈1.57 eV are observed and discussed.

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Phase relations along the Ag8GeS6–[(AgBr)4·GeS2] cross-section. Crystal structure and electric conductivity of Ag6GeS4Br2 in bulk

Cited by 4 publications

References 10 publications

Thermodynamic properties of saturated solid solutions of Ag7SnSe5Br and Ag8SnSe6 compounds in the Ag–Sn–Se–Br system measured by the EMF method

Thermodynamic properties of saturated solid solutions of Ag7SnSe5Br and Ag8SnSe6 compounds in the Ag–Sn–Se–Br system measured by the EMF method

Stability and ionic mobility in argyrodite-related lithium-ion solid electrolytes

Photoluminescence and electronic structure of α'-Ag8GeS6 crystals

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