Title :
Superconductivity and crystal structure peculiarities of the oxygen deficient YBa2Cu3O7-δ compounds
Author :
Yakhtar, V. G Bar ; Mikhailov, I.G. ; Morozovsky, A.E. ; Nemoshkalenko, V.V. ; Pan, V.M. ; Tolpygo, S.K. ; Vasilenko-Sheremetiev, M. ; Melnikov, V.S. ; Pshentsova, N.P.
Author_Institution :
Inst. of Metal Phys., Kiev, USSR
fDate :
3/1/1989 12:00:00 AM
Abstract :
Crystal structure peculiarities, oxygen atom and vacancy ordering, and superconducting properties of YBa2Cu3O7-δ compounds were investigated for the oxygen deficiency range O<δ<0.8. It was shown that the orthorhombic-to-tetragonal phase transition and oxygen-atom-ordering process are quite different phenomena and are observed at different temperature ranges. Oxygen disordering in the z=o plane is thermally activated and occurs mainly at low temperatures, when oxygen depletion by heating above 400°C leads to the significant local reduction of the negative charge at the z=o plane. To restore a charge balance, lattice negative and positive ions have to be driven to shift along the z-axis in opposite directions. These structure changes cause an increase in the distances between layers. The superconducting transition temperature Tc appears to decrease along with δ. Tc versus δ dependence has a two-step-like shape, for which an explanation is offered
Keywords :
barium compounds; crystal atomic structure of inorganic compounds; high-temperature superconductors; solid-state phase transformations; superconducting transition temperature; vacancies (crystal); yttrium compounds; YBa2Cu3O7-δ; crystal structure; high temperature superconductors; orthorhombic-to-tetragonal phase transition; transition temperature; vacancy ordering; Heating; Lattices; Minerals; Oxygen; Physics; Shape; Superconducting epitaxial layers; Superconducting transition temperature; Superconductivity; Temperature distribution;
Journal_Title :
Magnetics, IEEE Transactions on
