Calorimetric investigation of Tl5Te3 superconductivity

The specific heat of several samples in the γ phase of the Tl–Te system were measured between 1.8 and 4.2 °K to determine if the previously reported superconductivity in this phase was a true bulk effect or due to filaments of a second phase. These measurements show a change in the specific heat at Tc of the stoichiometric composition, Tl5Te3, which is 60% of the value predicted from the BCS theory. The only second phase present in some samples, as determined by x-ray diffraction, was TlTe; but even as large an amount present as 10% was found to make a very small contribution to the specific heat. Thus we conclude that Tl5Te3 is a bulk superconductor, characterized by an electronic specific heat of 5.7×10−3 cal/mole deg2 and a Debye ΘD of 96 °K. Some possible explanations are proposed to account for the low value of the measured specific heat.