Synthesis and properties of InxMo6Se8-yIy indium insertion compounds

Abstract

We present a study of the properties of the series InxMo6Se8-yIy (y=0.5, 1.0, 2.0) having the hexagonal-rhombohedral Mo6Se8 structure type. The materials were prepared by a low temperature (525 °C) insertion technique. For y=0.5, only the new superconducting phase In.5Mo6Se7.5I.5 was found. For y=1.0 and y=2.0, the InxMo6Se8-yIy phases represent the first Chevrel phases which are solid solutions with respect to indium insertion. InxMo6Se7I (0 < × < 1) presents a phase diagram which indicates phenomena associated with an In+1-In+3 valence change as x increases. InxMo6Se6I2 (0 < × < 0.66) is a well-behaved solid solution of In3+ in Mo6Se6I2. For both y=1.0 and y=2.0, an increase in In3+ concentration increases the rhombohedral angle into the 94°– 95° range and the hexagonal unit cell volumes into the range of 940 Å 3 at maximum indium concentrations. At higher temperatures, the indium abstracts iodide from the cluster units which then condense to form known phases with larger clusters. Even though Mo6X8 phases are stabilized by partial halogen substitution, attempts to synthesize niobium Chevrel-type phases stabilized by halogen-chalcogen substitution were unsucessful.