X-ray standing-wave analysis of the rare-earth atomic positions in RBa2Cu3O7−δ thin films

We applied the X-ray standing-wave technique to study the lattice location of rare-earth atoms in thin films of RBa2Cu3O7−δ (R=Gd, Pr). The films had a thickness of 200 nm and were grown by pulsed laser deposition on SrTiO3(001) substrates. The standing wave was generated by kinematic Bragg diffraction. The angular dependence of the R–L and Ba–L fluorescence yield was recorded while scanning through the (005) Bragg reflection of the film. Analysis of the angular dependence leads to information on the degree of site interchange of R and Ba. We found a clear indication that Pr substitutes for Ba.