Superconductivity in Y(Ba sub 1 minus y La sub y ) sub 2 Cu sub 3 O sub 9 minus. delta

Journal Article · Wed Apr 01 04:00:00 EST 1992 · Journal of Solid State Chemistry; (United States)

DOI:https://doi.org/10.1016/0022-4596(92)90033-R· OSTI ID:6959085

Karen, P; Fjellvag, H; Kjekshus, A ^[1]

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1. Univ. of Oslo, Blindern (Norway)

The superconducting properties of the Y(Ba{sub 1{minus}y}La{sub y}){sub 2}Cu{sub 3}O{sub 9{minus}{delta}} phase (note La solely substituting Ba) are studied over the entire homogeneity range, viz., 0.00 {lt} y {lt} 0.36(2) and 1.69(2) {lt} {delta} {lt} 3.00(2) for well-defined samples prepared by the citrate gel method and annealed at controlled partial pressures of O{sub 2}. Superconductivity (for T{sub c} {gt} 5 K, by ac susceptibility) is observed over a large range of compositions. In terms of oxygen content, the lower limit for superconductivity varies from 9{minus}{delta} {approx} 6.3 for y = 0.00 to 9{minus}{delta} {approx} 7.05 for y = 0.20. T{sub c} increases with increasing oxygen content (referring to the oxygen saturation limit 9{minus}{delta} = 6.95(1) + y for 320C at P{sub O{sub 2}} = 100 kPa), irrespective of the linkage of the copper-oxygen square chains when 9{minus}{delta} exceeds 7. For y = const., T{sub c} is hence correlated with the overall hole concentration p = (5 {minus} 2{delta} {minus} 2y)/3 per (Cu-O){sup p+}, and these correlations are in turn related to deformation of the structure. For p = const., T{sub c} decreases with increasing y, and a hole transfer from the Cu(2) to Cu(1) coordination sphere appears to be composed of: (1) a large contribution due to an increased number of oxygens bonded to Cu(1), (2) a smaller contribution associated with a decrease in orthorhombic deformation, and (3) an even smaller contribution (about half and of opposite sign to (2)) attached to decreased tetragonal deformation. The effects of La substitution are compared with those of Sr substitution, application of external pressure, and change in oxygen content. The occurrence of superconductivity is correlated with fractional occupancy of a single, non-bonding orbital leading to a metallic state, and this picture is discussed for various oxide systems.

• OSTI ID: 6959085
• Journal Information: Journal of Solid State Chemistry; (United States), Journal Name: Journal of Solid State Chemistry; (United States) Vol. 97:2; ISSN 0022-4596; ISSN JSSCB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360207* -- Ceramics
Cermets
& Refractories-- Superconducting Properties-- (1992-)
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
DATA
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
EXPERIMENTAL DATA
INFORMATION
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
STOICHIOMETRY
SUPERCONDUCTIVITY
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES