Powder XRD investigation of crystal structure modification effects on superconductivity in the Sn-doped YBa2Cu3-xSnxO7-delta systems

The relationships between the crystal structure modification, due to the do ping element of Sn, and the critical temperature T-c of Sn-doped YBa2Cu3-xS nxO7-delta with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, have been investigat ed by means of the peak shift and the peak broadening of the powder x-ray d iffraction pattern. The profiles of x-ray diffraction peaks, due to crystal planes (006), (020), (021) and (200), were studied using the multi-peak fi tting technique which is based on the Gaussian distribution function. It is interesting to note that the Sn-doped atoms effectively occupy the Cu2 sit es in the CuO2 layer. The critical temperature of the Y-123 phase depends m ore sensitively on the lattice parameters a and b, rather than on the c-axi s parameter c. The samples used for this investigation underwent the same t reatment to ensure the requirement for maintaining the same oxygen content, particle size and residual stress. In this way, we can make sure that the Sn doping basically causes the peak shift and the peak broadening. Based on our results, we conclude that Sn doping in YBCO leads to an increase of th e lattice constants a and b. The greater the expansion in a and b, the lowe r the critical temperature that results.