Solid-state chemistry of high-temperature oxide superconductors: the experimental situation

Journal Article · Sun May 01 04:00:00 EDT 1988 · J. Solid State Chem.; (United States)

DOI:https://doi.org/10.1016/0022-4596(88)90341-6· OSTI ID:6910939

Rao, C N.R.

High-temperature superconductivity in oxides of the type (La,Ln)/sub 2-x/Ba/sub x/(Sr)/sub x/CuO/sub 4/, Y(Ln)Ba/sub 2/Cu/sub 3/O/sub 7-delta/, La/sub 3-x/Ba/sub 3+x/Cu/sub 6/O/sub 14/, and related systems is discussed with emphasis on aspects related to experimental solid-state chemistry. All of these oxides possess perovskite-related structures. Oxygen-excess and La-deficient La/sub 2/CuO/sub 4/ also exhibit superconductivity in the 20-40 K just as La/sub 2-x/Ba/sub x/(Sr/sub x/)CuO/sub 4/; these oxides are orthorhombic in the superconductivity phase. The crucial role of oxygen stoichiometry in the superconductivity of YBa/sub 2/Cu/sub 3/O/sub 7-delta/ (T/sub c/ = 95 +/- 5 K) is examined; this oxide remains orthorhombic up to delta approx. = 0.6 and becomes tetragonal and nonsuperconducting beyond this value of delta. Oxygen stoichiometry in this and related oxides has to be understood in terms of structure and disorder. The structure of La/sub 3-x/Ba/sub 3+x/Cu/sub 6/O/sub 14/ is related to that of YBa/sub 2/Cu/sub 3/O/sub 7/, the orthorhombic structure manifesting itself when the population of O1 oxygens (along the Cu-O-Cu chains) is preponderant compared to that of O5 oxygens (along the a-axis); nearly equal populations of O1 and O5 sites give rise to the tetragonal structure. A transition from a high-T/sub c/ (95 K) superconductivity regime to a low-T/sub c/ (approx. 60 K) regime occurs in YBa/sub 2/Cu/sub 3/O/sub 7-delta/ accompanying a change in delta. There is no evidence for Cu/sup 3 +/ in these nominally mixed valent copper oxides. Instead, holes are present on oxygens giving rise to O/sup -/ or O/sub 2//sup 2 -/ species, the concentration of these species increasing with the lowering of temperature. Certain interesting aspects of the superconducting oxides such as domain or twin boundaries. Raman spectra, microwave absorption, and anomalous high-temperature resistivity drops are presented along with the important material parameters.

• Research Organization: Indian Institute of Science, Bangalore
• OSTI ID: 6910939
• Journal Information: J. Solid State Chem.; (United States), Journal Name: J. Solid State Chem.; (United States) Vol. 74:1; ISSN JSSCB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202 -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ABSORPTION SPECTROSCOPY
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTROMAGNETIC RADIATION
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
LASER SPECTROSCOPY
LOW TEMPERATURE
MICROWAVE RADIATION
ORTHORHOMBIC LATTICES
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
PHYSICAL PROPERTIES
RADIATIONS
RAMAN SPECTROSCOPY
RARE EARTH COMPOUNDS
SPECTROSCOPY
STRONTIUM COMPOUNDS
STRONTIUM OXIDES
STRUCTURAL CHEMICAL ANALYSIS
SUPERCONDUCTIVITY
TRANSITION ELEMENT COMPOUNDS
VERY LOW TEMPERATURE