Db. Currie et Mt. Weller, THE CRYSTAL-STRUCTURES OF DY2BA4CU7O14- A HIGH-RESOLUTION POWDER NEUTRON-DIFFRACTION STUDY(DELTA AND ND2BA4CU7O14+DELTA ), Physica. C, Superconductivity, 216(1-2), 1993, pp. 140-146
The structures of Dy2Ba4Cu7O14+delta and Nd2Ba4Cu7O14+delta (247), whi
ch can be considered to be derived from alternate blocks of the LnBa2C
u3O7 (123) and LnBa2Cu4O8 (124) structures, have been refined using hi
gh resolution powder neutron diffraction data. Accurate structural par
ameters, determined by this oxygen-sensitive technique, are presented
for these superconducting oxides. In both materials oxygen was found t
o be randomly distributed over the formally single chain and inter-cha
in sites of the type seen in 123 compounds; no crosslinking of the 124
double chains was observed. Notable differences in oxygen contents we
re found between the two samples; the neodymium sample exhibited a hig
h average copper oxidation state as a result of considerable occupancy
of both of the chain and inter-chain sites. The orthorhombic distorti
ons of these materials are markedly reduced compared to those recorded
for the corresponding 123 and 124 materials. A flattening of the copp
er-oxygen planes sandwiching the lanthanide site with increasing lanth
anide size, as previously found in Ln123 and Ln124 compounds, is obser
ved.