INVESTIGATION OF A NANOCRYSTALLINE YBA2CU3O7-DELTA POWDER BY NEUTRON AND ELECTRON DIFFRACTIONS

The structural characterization of a submicron-sized YBaCuO powder sam ple, obtained by freeze-drying preparation, was carried out using neut ron diffraction from room temperature down to liquid helium temperatur e. A temperature independent broadening of the diffraction lines indic ates a finite size of about 40 nm for the diffracting domains. No orth orhombic strain anomaly in the vicinity of the critical temperature T- c was detected. The unit cell volume reduction in the whole range 300- 4.2 K, delta V congruent to 2.1 Angstrom(3), is larger than previously published values. High resolution electron diffraction confirms the e xistence of well-ordered crystalline domains with a size reaching ten nanometers. In addition, some electron diffraction patterns exhibit su perlattice reflections, the origin of which will be discussed.