Directed Dehydration as Synthetic Tool for Generation of a New Na4SnS4 Polymorph: Crystal Structure, Na+ Conductivity, and Influence of Sb-Substitution

We present the convenient synthesis and characterization of the new ternary thiostannate Na4SnS4 (space group I4(1)/acd) by directed removal of crystal water molecules from Na4SnS4 center dot 14H(2)O. The compound represents a new kinetically stable polymorph of Na4SnS4, which is transformed into the known, thermodynamically stable form (space group P (4) over bar2(1)c) at elevated temperatures. Thermal co-decomposition of mixtures with Na3SbS4 center dot 9H(2)O generates solid solution products Na4-xSn1-xSbxS4 (x=0.01, 0.10) isostructural to the new polymorph (x=0). Incorporation of Sb5+ affects the bonding and local structural situation noticeably evidenced by X-ray diffraction, Sn-119 and Na-23 NMR, and Sn-119 Mossbauer spectroscopy. Electrochemical impedance spectroscopy demonstrates an enormous improvement of the ionic conductivity with increasing Sb content for the solid solution (sigma(25 degrees C)=2x10(-3), 2x10(-2), and 0.1 mS cm(-1) for x=0, 0.01, and 0.10), being several orders of magnitude higher than for the known Na4SnS4 polymorph.

Automated summary

This study presents the synthesis and characterization of a new polymorph of Na4SnS4, Na4SnS4 (space group I4(1)/acd), by removing crystal water molecules. Incorporation of Sb5+ significantly improves the ionic conductivity of the solid solution.