S. A. Mahmoud

Thermal expansion measurements using x-ray powder diffraction of Tl-1223 substituted by molybdenum

Lattice parameters and the volume thermal expansion coefficient, from room temperature down to 80 K, have been calculated for TlBa2Ca2Cu3−xMoxO9−δ with x = 0.0, 0.05, 0.1 and 0.2 using x-ray powder diffraction. The superconducting transition temperature for the prepared samples, determined from electrical resistivity measurements, is suppressed from 122 to 98 K as the Mo content increases from 0.0 to 0.2. This suppression is discussed in terms of the uniaxial pressure induced by the changing of the Jahn–Teller effect and the hole-filling mechanism. The lattice parameters a and c contract with decreasing temperature and the rate of contraction of the lattice parameter a (a80/a300 = 0.9997) is lower than that of c (c80/c300 = 0.9967). The volume thermal expansion coefficient increases from 4.6 × 10−5 to 6.04 × 10−5 K−1 as x increases from 0.0 to 0.2. The Debye temperature, calculated from volume thermal expansion coefficient measurements, is reported as a function of Mo content and superconducting transition temperature and it agrees with that determined from specific heat measurements.