Influence of crystal structure disordering on ionic conductivity of Ag7+x(P1−xGex)S6 single crystals

• Published in: Journal of alloys and compounds 2022-12, Vol.926, p.166873, Article 166873
• Main Authors: Pogodin, A.I., Filep, M.J., Studenyak, V.I., Symkanych, O.I., Stercho, I.P., Izai, V.Yu, Kokhan, O.P., Kúš, P.
• Format: Article
• Language: English
• Subjects: Conductors; Crystal growth; Crystal structure; Crystallization; Disordered systems; Electrical resistivity; Electrochemical impedance spectroscopy; Ion currents; Ion transport; Ionic conduction; Phase diagrams; Rietveld method; Single crystals; Solid solutions
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.166873

We present a detailed study of Ag7+x(P1−xGex)S6 (x = 0.1; 0.25; 0.33; 0.5; 0.75) single crystals of novel superionic conductors with argyrodite structure. The single crystals on superionic conductors Ag7+x(P1−xGex)S6 were grown by directional crystallization technique. The crystal structure of Ag7+x(P1−xGex)S6 solid solutions was studied by the Rietveld refinement method. It was found that solid solutions crystallize in three SGs: P213 (x = 0.1), F-43m (x = 0.25; 0.33) and Pna21 (x = 0.5; 0.75). Ag7+x(P1−xGex)S6 solid solutions are characterized by the presence of Ag positions with partial occupancy, which is different from the initial ternary compounds. The frequency and temperature dependences of electrical conductivity were studied by electrochemical impedance spectroscopy method. The structural disordering caused by P+5↔Ge+4 heterovalent cationic substitution induces increasing ionic conductivity of the solid solutions by 5 orders of magnitude. The occurrence of favorable conditions for ion transport is explained using simple structural descriptors. [Display omitted] •A new system of solid electrolytes based on argyrodites Ag7+x(P1−xGex)S6 was studied.•The homogeneity ranges and structure of three types solid solutions were determined.•Applying the P5+↔Ge4+ substitution the ionic conductivity is increased by 104-105 times.•Impact of P5+↔Ge4+ substitution on crystal structure and conductivity is discussed.