M. Me. Barakat

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.

Superconducting parameter determination for (Co0.5Zn0.5Fe2O4)x/Cu0.5Tl0.5-1223 composite

The addition of magnetic Co0.5Zn0.5Fe2O4 nanoparticles to the superconducting Cu0.5Tl0.5-1223 phase has been used to investigate the electrical resistivity behavior of the composite above the superconducting transition temperature Tc. This was studied according to the opening of spin gap and fluctuation conductivity. The results indicated that the pseudogap temperature (T*) and superconducting fluctuation temperature (Tscf) change by increasing the addition of Co0.5Zn0.5Fe2O4 nanoparticles. It was found that T* is related to hole carrier concentration P and it also depends on the antiferromagnetic fluctuation affected by magnetic nanoparticles. The excess-conductivity analysis showed four different fluctuation regions started from high temperature up to Tc, and they were denoted by short wave (sw), two-dimensional (2D), three-dimensional (3D), and critical (cr) fluctuations. The crossover temperature between 3D and 2D (T3D–2D) in the mean field region was decreased by increasing the addition of Co0.5Zn0.5Fe2O4 nanoparticles, in accordance with the decrease in Tscf with x. The coherence length at 0 K along c-axis ξc(0), effective layer thickness of the 2D system d, and inter-layer coupling strength J were estimated as a function of Co0.5Zn0.5Fe2O4 nanoparticle addition. Moreover, the thermodynamics, lower and upper critical magnetic fields, as well as critical current density have been calculated from the Ginzburg number NG. It was found that the low concentration of Co0.5Zn0.5Fe2O4 nanoparticles up to x = 0.08 wt% improves the superconducting parameters of Cu0.5Tl0.5-1223 phase. On the contrary, these parameters were deteriorated for (Co0.5Zn0.5Fe2O4)x/Cu0.5Tl0.5-1223 composite with x > 0.08 wt%.