STRUCTURE AND MICROSTRUCTURE IN NANOCRYSTALLINE YBA2CU3O7-DELTA POWDER

Freeze drying technique is a new method developed to condense nanocrys talline particles. It has been applied to get submicro-sized YBaCuO po wders about 150 nm that is the same order than the London penetration depth lambda(L). Structural analysis by Neutron Diffraction displays a smaller orthorhombic unit cell volume (V congruent to 172.82 Angstrom (3)) associated with a large temperature dependence delta V congruent to-2.1 Angstrom(3) over the whole range 300-4.2 K. The increase of the line profile widths in the neutron diffraction patterns, which is tem perature independent, may be interpreted as geometrical coherent domai n size of about 400 Angstrom. Such a result has been illustrated by th e way of the High Resolution Electron Microscopy (HREM). The origin of the presence of the superlattice reflections in some Electron Diffrac tion patterns and their possibly correlations with electronic and magn etic properties would be discussed.