Effects of Pressure on the Superconducting Transition Temperatures of Sn, In, Ta, Tl, and Hg

Solid parahydrogen has been used as a transmitter of approximately hydrostatic pressure to study the effects of pressures up to 10 000 atmos on the superconducting transition temperatures of polycrystalline tin, indium, tantalum, thallium, and mercury. The technique which was used allowed an approximate evaluation of the effects of sample deformation and pressure gradients, and the results are considerably more accurate than the high-pressure data previously available. The transition temperature data for tin and indium showed considerable curvature when plotted vs pressure, but gave a roughly linear relationship when plotted against volume. No curvature was found for tantalum. The thallium data agree qualitatively with previous work, and show a maximum in the transition temperature vs pressure curve at about 2000 atmos. The mercury results were anomalous in that two distinct transition temperature vs pressure curves (with different zero-pressure transition temperatures) were found; one when the pressure was kept below 4000 atmos, and the other when the sample was cycled from zero to 10 000 atmos. Other experiments have shown that these results are due to two different modifications of solid mercury, each of which can exist at liquid helium temperatures.