Effect of pressure and oxygen defects in divalent Chevrel-phase superconductors

The pressure dependence of the superconducting transition temperature Tc is measured for several samples each of the divalent Chevrel-phase systems SnMo₆{S}₈$, Pb${Mo}₆S₈, and EuMo₆{S}₈$. The pressure dependence of ${T}c$ scales with ${T}c$ and each system has the same scale factor. The data are discussed in terms of oxygen defects systematically introduced into each system and in terms of the lattice constants. Oxygen defects inadvertently introduced into Chevrel-phase superconducting systems may account for the wide variation of Tc quoted in the literature.