Abstract
The structures of Dy 2Ba 4Cu 7O 14+δ and Nd 2Ba 4Cu 7O 14+δ (247), which can be considered to be derived from alternate blocks of the LnBa 2Cu 3O 7 (123) and LnBa 2Cu 4O 8 (124) structures, have been refined using high resolution powder neutron diffraction data. Accurate structural parameters, determined by this oxygen-sensitive technique, are presented for these superconducting oxides. In both materials oxygen was found to be randomly distributed over the formally single chain and inter-chain sites of the type seen in 123 compounds; no crosslinking of the 124 double chains was observed. Notable differences in oxygen contents were found between the two samples; the neodymium sample exhibited a high average copper oxidation state as a result of considerable occupancy of both of the chain and inter-chain sites. The orthorhombic distortions of these materials are markedly reduced compared to those recorded for the corresponding 123 and 124 materials. A flattening of the copper-oxygen planes sandwiching the lanthanide site with increasing lanthanide size, as previously found in Ln123 and Ln124 compounds, is observed.
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