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The reactions of potassium polysulfides with elemental Nb were investigated with different analytical techniques. The amount of the polysulfide applied has no influence onto product formation, i. e. the ratio K 2 S x : Nb is not important. The length of the polsysulfide chain, i. e. the value of x in K 2 S x  determines what product is formed. In sulfur-poor melts, K 3 NbS 4  is observed. Increasing x to 5 - 6, K 4 Nb 2 S 11  is formed with a structure containing S 2  2−  anions. Finally, applying a melt with x &gt; 6, K6Nb4S25 is found as the product with a crystal structure containing the S 5  2−  polysulfide anion. When K 2 S x  (x &lt; 5) is heated with sulfur in the first step the pentasulfide K 2 S 5  is formed. Immediately after melting of K 2 S 5  a reaction with elemental Nb occurs. The results of FT-IR and X-ray investigations have demonstrated that after oxidation the anion [Nb 2 S 11 ] 4−  is formed relatively fast, and after a short time crystalline K 4 Nb 2 S 11  can be detected. After 24 h the reaction is complete.

zeitschrift für naturforschung b

Reactions in Molten Alkalimetal Polychalcogenides: What Happens in the Melt? A Study of the Reactions in the System K-Nb-S Using Differential Scanning Calorimetry, Infrared Spectroscopy, and X-Ray Powder Diffraction