Structural features of a low-T-c nearly; stoichiometric Nd1+xBa2-xCu3Oz pha
se (x less than or equal to 0.05, z similar to 6.9, a = 3.897-3.899 Angstro
m, b = 3.902-3.908 Angstrom, c = 11.707-11.719 Angstrom) have been investig
ated for the first time by XRD, EXAFS structure refinement techniques and R
aman spectroscopy. It has been found that the abnormal lattice parameters a
nd the low superconductivity transition temperature (55 K) of such a phase
are related to structural disorder in the Ba and Nd sites resulting in oxyg
en disordering which cannot be avoided by a standard oxidation procedure. I
t is shown that longer annealing at high temperatures is an important facto
r for reducing the oxygen disordering and hence enhancing superconducting p
roperties after oxidation. (C) 2000 Elsevier Science B.V. All rights reserv
ed.