{sup 17}O and {sup 135,137}Ba NMR study of oxide superconductors

Thesis/Dissertation · Fri Dec 31 04:00:00 EST 1993

OSTI ID:111305

Shore, J S

A series of oxide superconductors and related compounds, including: BaPbO{sub 3}, BaBiO{sub 3}, BaSb{sub 0.25}Pb{sub 0.75}O{sub 3}, BaBi{sub 0.25}Pb{sub 0.75}O{sub 3}, Ba{sub 0.6}K{sub 0.4}BiO{sub 3}, Bi{sub 2}Sr{sub 2}CuO{sub 6+x}, La{sub 1.85} Ca{sub 0.15} CuO{sub 4-x}, La{sub 1.85}Sr{sub 0.15} CuO{sub 4-x}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}, YBa{sub 2}Cu{sub 3}O{sub 7-x}, and Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8+x}, were studied using solid state {sup 17}O and {sup 135,137}Ba nuclear magnetic resonance (NMR) spectroscopy. the measurements are related to the compounds` atomic, electronic and magnetic structures. The {sup 17}O NMR results indicate that most of the oxide superconductors are inhomogeneous, and have longitudinal relaxation mechanisms that are magnetic in origin. Variable temperature measurements of the bismuthate and plumbate materials are consistent with the relaxation being dominated by the oxygen 2p character of the conduction band. While similar measurements of the CuO{sub 2} planar oxygen, of the cuprates, indicate that their relaxation is dominated by a contact interaction. The relaxation rates of the bismuthate and plumbates vary with T{sub c}, consistent with a relation derived from the Bardeen-Cooper-Scheifer (BCS) theory of superconductivity. The relaxation rates of the cuprates are fairly constant (T{sub 1}T {approx} 3.9 {+-} 1.5 sK), even though the transition temperatures range from 5.6 to 95 K. Finally, from a comparison with the copper relaxation measurements of other groups, its is determined that the copper spin fluctuations are localized near the reciprocal lattice vector ({pi}/a,{pi}/a). From {sup 135,137}Ba NMR and NQR measurements of YBa{sub 2}Cu{sub 3}O{sub 7-x}, the electric field gradient is determined and found to be consistent with ab initio calculations. Also it is determined from variable temperature relaxation measurements, that the barium site is effected by the CuO{sub 2} planar spin fluctuations.

• Research Organization: Illinois Univ., Urbana, IL (United States)
• OSTI ID: 111305
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
40 CHEMISTRY
66 PHYSICS
BARIUM 135
BARIUM 137
COPPER OXIDES
HIGH-TC SUPERCONDUCTORS
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
OXYGEN 17
YTTRIUM COMPOUNDS