Superconductivity and stability of near equiatomic V-Ru compounds at high pressure

The variation of T c for the V-Ru compounds over the composition range 42 to 47.5 at % Ru has been investigated for hydrostatic pressures up to 25kbar. At zero pressure T c peaks sharply between 45.5 and 46 at % Ru, with a subsidiary peak occurring about 44 at %. Heat treatment significantly influences the value of T c For the cubic, B2 structure compounds with less than 45 at % RuT c follows a slight linear decrease under pressure. At Ru concentrations greater than 45.5 at %, for which the crystal structure undergoes a tetragonal distortion at zero pressure, there is a dramatic change in the pressure dependence of T c which becomes strongly positive. This behaviour is discussed in relation to the pressure induced stability of the cubic structure.