Title :
Oxidation kinetics in oxygen deficient YBa2Cu3O7-x studied by neutron powder diffraction
Author :
Als-Nielsen, J. ; Andersen, N.H. ; Broholm, C. ; Clausen, K.N. ; Lebech, B. ; Nielsen, M. ; Poulsen, H.F.
Author_Institution :
Dept. of Phys., Riso Nat. Lab., Roskilde, Denmark
fDate :
3/1/1989 12:00:00 AM
Abstract :
A high-resolution, multidetector neutron powder diffractometer has been constructed and used for online studies of the oxidation kinetics in ceramic powders of oxygen-deficient YBa2Cu3O 7-x (YBACUO). The structural phase transition between ordered orthorhombic and disordered tetragonal phase has been studied in pure oxygen and under vacuum. A continuous transition at 655°C is observed in a pure oxygen atmosphere under equilibrium conditions, whereas an irreversible transition is observed at 470°C under vacuum. Reduced YBACUO corresponding to x≈1.0 has been obtained by evacuation at 705°C and has been shown to be stable in air. The oxidation processes of reduced YBACUO in a pure oxygen atmosphere have been studied using a semidynamical stepwise increase in temperature and under isothermal conditions. The results show that the in-diffusion under oxidation of reduced YBACUO is more easily accomplished than the corresponding out-diffusion process under reduction. From the structural data it is concluded that oxidation takes place in a mixed-phase medium of coexisting tetragonal and orthorhombic phases
Keywords :
barium compounds; high-temperature superconductors; neutron diffraction examination of materials; oxidation; solid-state phase transformations; yttrium compounds; YBa2Cu3O7-x; ceramic powders; high temperature superconductors; neutron powder diffraction; orthorhombic; oxidation kinetics; structural phase transition; tetragonal; Atmosphere; Ceramics; Diffraction; Isothermal processes; Kinetic theory; Neutrons; Oxidation; Powders; Temperature; Yttrium barium copper oxide;
Journal_Title :
Magnetics, IEEE Transactions on
