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States of oxygen ordering in YBa/sub 2/Cu/sub 3/O/sub z/

Conference ·
OSTI ID:5889838
The compound YBa/sub 2/Cu/sub 3/O/sub z/ (1-2-3) was the first one whose superconducting transition temperature exceeded the technologically important temperature of 77K. Actually, the 1-2-3 compound at close to oxygen stoichiometry z = 7 became superconducting at about T/sub c/ = 90K, with T/sub c/ dropping by increments as z decreased from the value 7. In the 90K superconducting phase, occupied sites form O--Cu--O chains, and the resulting three-dimensional structure has orthorhombic symmetry. When available sites in the mirror plane are occupied statistically by O ions, the resulting structure has tetragonal symmetry and the material is nonsuperconducting. It thus appears that the tetragonal to orthorhombic transition in the 1-2-3 compound can be modeled by an order-disorder transition in the mirror plane. It is the object of this paper to review the properties of this transition and to derive appropriate phase diagrams pertaining to oxygen ordering in the plane. Much pertinent information concerning oxygen ordering in 1-2-3 is reviewed in a recent paper by Beyers and Shaw. 37 refs., 8 figs.
Research Organization:
Lawrence Berkeley Lab., CA (USA)
DOE Contract Number:
AC03-76SF00098
OSTI ID:
5889838
Report Number(s):
LBL-27267; CONF-890480-1; ON: DE89014893
Country of Publication:
United States
Language:
English