Investigation of specific heat and thermopower properties of Tl-1223 substituted by sodium

Specific heat and thermopower measurements are carried out for a series of high-temperature superconductor samples of type TlBa2Ca2−xNaxCu3O9−δ with 0≤x≤0.4. The thermopower coefficient is measured as a function of temperature from room temperature down to liquid nitrogen temperature, 77 K, using a standard differential technique. The results are analyzed according to the two-band model (Fermi-liquid model) and the two-band model with an extra linear term. The specific heat is measured from room temperature down to 10 K using a physical property measurement systems (PPMS, Quantum Design). The specific heat data for all prepared samples do not show any discontinuity change at the superconducting transition temperature, indicating the high anisotropy of Tl-1223. The Debye temperature, calculated from the specific heat measurements, is temperature dependent and depends on the Na content. Finally, a relation between the Debye temperature and the superconducting transition temperature is reported to explain the suppression of superconductivity of Tl-1223 due to sodium substitution.