Real space and Q space analysis of local disorder induced by Al doping in the SmBa2Cu3O6+d superconductor

The cation substitutions for copper in RBa2Cu3O6+d (R = Y, Ln; 0 < d < 1) high Tc superconductors are widely studied in order to understand their physical properties [1]. In particular Al seems to be a suitable dopant because: i) it is a non-magnetic ion; ii) it substitutes for copper only on Cu1 (0,0,0) site, far from the superconducting planes; iii) its valence state is fixed, making simple the calculation of the total hole concentration; iiii) it is possible to vary the medium range structure of the superconductor throughout an aluminium-clustering process [2]. However, Aluminium doping introduces local disorder in the structure because of its different valence (+3 instead of +1/+2) and local environment (tetrahedric instead of square planar) in respect to copper. In order to fully understand the effect of Al doping on the physical properties of RBa2Cu3O6+d superconductors the nature of this disorder has to be defined. To do so we have investigated some SmBa2Cu3-xAlxO6+d samples with different Al concentration (x=0, 0.15, 0.33), annealed either in oxidising or in reducing conditions. The long and short range structure of the samples have been determined through the parallel real pace (PDF) and Q space (Rietveld) analysis of XRPD patterns obtained at the ID31 beamline of ESRF facility. References [1] See, for instance, M.S. Skakle, Mater. Sci. Eng., R23, 1 (1998) and references therein [2] M. Scavini, M. Daldosso, S. Cappelli, C. Oliva, M. Brunelli, C. Ferrero, A. Lascialfari, Europhys. Lett., 76(3), (2006) 443-449