Metal molybdenum tellurides: Synthesis, characterisation and superconducting properties of compounds of the type Mo6− xMxTe8 ( M = Ru or Rh)

Abstract

Details of the synthesis of pure compounds of composition Mo 6− x MTe 8, M = Ru, Rh, are reported for the first time. The hexagonal lattice parameters and unit cell volumes are shown by powder X-ray diffraction to vary steadily with increasing valence electron count per formula unit. The results are consistent with the substitution of ruthenium or rhodium in the Mo 6 octahedron within the Mo 6Te 8 unit. Heat capacity measurements show that the incorporation of small amounts of ruthenium into the Mo 6Te 8 unit induces the onset of superconductivity at temperatures exceeding 2K. Estimates of ( dHc 2 dT ) T c for Mo 5Ru 1Te 8 and Mo 5.5Ru 0.5Te 8 are of the same order of magnitude as those observed for sulphur- and selenium- containing Chevrel phase compounds.