Evidence of Gd substitution for Y in YBCO films with Gd excess

Gd-YBa${}_2$Cu${}_3$O${}_{7-\delta }$ (Gd-YBCO) thin films with 10 mol% and 20 mol% excess-Gd concentration with respect to Y were investigated at the Gd L${}_3$ and Y K core absorption edges by EXAFS spectroscopy with the aim of determining
the local structure of the Gd dopant. To this purpose, EXAFS data were collected also on Gd-Ba${}_2$Cu${}_3$O${}_{7-\delta }$ (GdBCO) and pristine YBCO films and on Gd${}_2$O${}_3$ and Y${}_2$O${}_3$ model compounds for comparison with the YBCO films with Gd excess. The EXAFS analysis was based on Y and Gd oxides as well as on a cluster obtained by Density Functional Theory (DFT) where Gd atoms were inserted substitutional to Y atoms. The EXAFS data clearly reveal the incorporation of Gd in the lattice as substitute of Y and no evidence of segregated Gd oxide was found within the film matrix.