Metal atom incorporation studies on A<inf>x</inf>Mo<inf>6</inf>S<inf>8</inf> Chevrel phases

Group IIIa metals and Nb, Hg and Pb containing AxMo6S8 Chevrel phases have been synthesized by low temperature reaction (420-430°C) frorn A metal and Mo6S8. Some of these phases are hitherto unknown. Electrolysis method of preparation of AxMo6S8 reported by Schöllhorn does not yield the desired phases when A = Pb or Ag. Stoichiometry, thermal stability, electrical and superconducting properties of the compounds have been examined. In the PbxMo6S8 system, a series of phases with varying x have been prepared and studied. Group IIIa metal and Nb-compounds are found to be semiconductors with low energies of activation exhibiting p-type behavior in the range 77-300 K. Hg-phase behaves as a metal or a degenerate semiconductor and does not become superconducting above 4.2 K. X-Ray, resistivity and Tc studies show that for x ≤ 0.8 in PbxMo6S8, the compounds behave more like Mo6S8 and only for x ≅ 1.0 or (PbBi)1.0, the inherent behavior of the ternary Chevrel phase is exhibited. Seebeck coefficients are small and positive for Mo6S8, Cu and Pb-containing phases in the range 77-300 K. The results are discussed in the light of available band structure of these materials. © 1980.