Structure and microstructure in nanocrystalline YBa2Cu3O7−δ powder

Freeze drying technique is a new method developed to condense nanocrystalline particles. It has been applied to get submicro-sized YBaCuO powders about 150 nm that is the same order than the London penetration depth λL. Structural analysis by Neutron Diffraction displays a smaller orthorhombic unit cell volume (V ≅ 172.82 A3) associated with a large temperature dependence δV ≅ −2.1 A3 over the whole range 300–4.2 K. The increase of the line profile widths in the neutron diffraction patterns, which is temperature independent, may be interpreted as geometrical coherent domain size of about 400 A. Such a result has been illustrated by the way of the High Resolution Electron Microscopy (HREM). The origin of the presence of the superlattice reflections in some Electron Diffraction patterns and their possibly correlations with electronic and magnetic properties would be discussed.