Synthesis and properties of In(x)Mo(6)Se(8-y)I(y) indium insertion compounds.

We present a study of the properties of the series In(x)Mo (6) Se(8-y)I(y)(y=0.5, 1.0, 2.0) having the hexagonal-rhombohedral Mo(6)Se(8) structure type. The materials were prepared by a low temperature (525C) insertion technique. For y=0.5, only the new superconducting phase In(.5)Mo(6)Se(7.5)I(.5) was found. For y=1.0 and y=2.0, the In(x)Mo(6)Se(8-y)I(y) phases represent the first Chevrel phases which are solid solutions with respect to indium insertion. In(x)Mo(6)Se(7)I(01) presents a phase diagram which indicates phenomena associated with an In(+1)- In(+3) valence change as x increases. In(x)Mo (6)Se(6)I(2) (00.66) is a well-behaved solid solution of In(3+) in Mo (6)Se(6)I(2). For both y=1.0 and y=2.0 an increase in In(3+) concentration increases the rhombohedral angle into the 94D -95D range and the hexagonal unit cell volumes into the range of 940 Angstroms (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 Mo(6)X(8) phases are stabilized by partial halogen substitution, attempts to synthesize niobium Chevrel- type phases stabilized by halogenchalcogen substitution were unsuccessful.