Abstract :
The Nd(Ba1−xNdx)2Cu3O7+δ solid solution, Nd123ss, has been investigated by neutron powder diffraction and Rietveld analysis. It is confirmed that the crystal structure of its Nd-rich limit, Nd(Ba0.55Nd0.45)2Cu3O7.33, is satisfactorily described in the space group Bmmm (a=7.7679(3), b=3.8542(1), and c=22.9590(9) Å). The fourfold superstructure with respect to the orthorhombic cell of YBCO is due to ordering between Ba and Nd atoms in the bridging layer. Differences with previous works concern exclusively the distribution of O atoms in the ‘chain’ layer. Our results give strong indications that ordering also occurs for lower Nd contents.
