Superconductivity of divalent Chevrel phases at very high pressures

Abstract

The electrical resistivity and the superconducting transition temperatures were examined for three representative divalent Chevrel phase systems, SnMo6S8, EuMo6S8, and BaMo6S8, as a function of hydrostatic pressure to 2 GPa and in quasihydrostatic pressures to 10 GPa. In all systems, Tc is depressed to 0 K for sufficiently large pressures. For the Sn- and Eu-based systems, both highly purified samples and samples with controlled oxygen content were used. In an oxygenated SnMo6S8 sample (less than 3% O2 substituted for the S atoms) the pressure threshold and maximum Tc are 40% lower than in the pure sample, but for P>3.5 GPa the Tc-P phase diagrams nearly coincide, with Tc reaching zero at an extrapolated pressure of about 12 GPa. In pure EuMo6S8, superconductivity appears only above a threshold pressure of about 1 GPa and is depressed to 0 K above 4.5 GPa. In an oxygenated sample the maximum Tc and the threshold pressure are depressed, and above about 3.5 GPa the Tc-P phase diagrams coincide, as in the Sn-based system, although Tc is then rapidly depressed to 0 K at about 4.5 GPa. In a highly purified BaMo6S8 sample superconductivity appears above about 2 GPa and is depressed to 0 K at extrapolated pressures above 12 GPa. A full transition to the zero-resistance superconducting state is observed in BaMo6S8. The data are discussed in terms of a model linking the rhombohedral-to-triclinic structural transition, the superconducting transition temperature, and the role of pressure in suppressing the structural transition.

Source-reported materials — not catalogue approval

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