An X-ray Powder Diffraction Study of Sr₂LnTaCu₂O₈, Ln = Nd, Sm, Eu, Gd

A series of oxides of the composition Sr₂LnTaCu₂O₈, Ln = Nd, Sm, Eu, Gd has been prepared and characterized by X-ray powder diffraction. Samples are tetragonal, space group P4/mmm and isostructural with a perovskite-like phase Ba₂LaTaCu₂O₈. The unit-cell parameters have been determined using Mo or Si as internal standard. The structure of Sr₂SmTaCu₂O₈ has been refined by the Rietveld method. X-ray diffraction patterns of the samples and the crystal structure of Sr₂SmTaCu₂O₈ showed ordering of Ta and Cu ions: the octahedrally coordinated Ta ion is on the Cu(1) site, while Cu ions remain on the Cu(2) sites of the Ba₂YCu₃O_7−δ-type structure. (Powder Diffraction File Nos. 46–1490 for Sr/NdTaCu₂O₈, 46-1489 for Sr₂SmTaCu₂O₈, 46-1488 for Sr₂EuTaCu₂O₈ and 46-1487 for Sr₂CdTaCu₂O₈.