Physical properties of several M 2Mo 6X 6 compounds (M = GROUP IA METAL; X = Se, Te)

Abstract

We report the physical properties of the pseudo one dimensional ternary molybdenum chalcogenides M 2Mo 6X 6 (M = K, Rb,Cs,Tl;X = Se, Te) measured on single crystals grown at high temperature. For Group IA metals (Rb,..,Cs) the transport properties evolve from a metallic to a semiconducting-like behavior on decreasing the temperature. Over the same temperature range the Group IIIA compound (Tl 2Mo 6Se 6) remains metallic and even superconducts at 5.1K. The susceptibility of these materials is weakly diamagnetic and does not reveal anomalied correlated to the onset of the broad metal-nonmetal transition, except perhaps for Cs 2Mo 6Te 6. A variation of the electronic interchain coupling is proposed to explain the difference between the Group IA and IIIA metal compounds. In the absence of evidence of three dimensional ordering at low temperature, we suggest that the broad metal-nonmetal transition is due to a fluctuating Pierls gap that is uncorrelated from one Mo chain to the next.