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

We applied the X-ray standing-wave technique to study the lattice location of rare-earth atoms in thin films of RBa2Cu3O7-delta (R = Gd, Pr). The film s had a thickness of 200 nm and were grown by pulsed laser deposition on Sr TiO3(001) substrates. The standing wave was generated by kinematic Bragg di ffraction. The angular dependence of the R-L and Ba-L fluorescence yield wa s recorded while scanning through the (005) Bragg reflection of the film. A nalysis of the angular dependence leads to information on the degree of sit e interchange of R and Ba. We found a clear indication that Pr substitutes for Ba. (C) 2000 Elsevier Science Ltd. All rights reserved.