High pressure study on quasi-one-dimensional compounds M₂Mo₆X₆

We have investigated resistively the M₂Mo₆X₆ polycrystalline compounds under pressures up to 160 kbar down to 1 K. The broad M-I transition and the activation energy during the transition are suppressed monotonically by pressure. Superconductivity has been induced in K₂Mo₆Se₆, K₂Mo₆Te₆, Na₂Mo₆Te₆, Na₂Mo₆Se₆ and Rb₂Mo₆ Se₆ by pressure with a transition temperature T_c between 1 and 4 K. A large resistance-increase prior to the superconducting transition is always observed. While the critical pressure for the induction of superconductivity depends on M, the T_c-behavior under pressure is affected only by X.