X-ray diffraction anomalies and random intercalation in H-loaded Y-Ba-Cu-O films

A model has been developed to account for the structural peculiarities observed by X-ray diffraction of hydrogen-loaded Y123 films deposited in an O₂/Ar+H₂O atmosphere. The model considers the random inter-growth of two very similar structures with slightly different c-axis or, equivalently, the random intercalation of a small spacer in the Y123 matrix causing displacement disorder along the c-axis direction. It quantitatively reproduces both the nonmonotonous deviations of Bragg-peaks and their progressive weakening and broadening for higher diffraction orders. The model offers the possibility to evaluate both the fraction of secondary phase and its c-axis lattice parameter. In the example given, we have been able to identify 28% of intercalated hydrogen bronze H_0.66[Y123] with 4% elongated c-axis. A simplified procedure for the diagnosis and characterization of random intercalates is extracted from the model. Similar structures observed in other perovskite-based layered oxides are discussed within this framework.