Oxygen-17 and Barium-135,137 NMR Study of Oxide Superconductors

Shore, Jay Sanford

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https://hdl.handle.net/2142/72280 Copy

Description

Title

Oxygen-17 and Barium-135,137 NMR Study of Oxide Superconductors

Author(s)

Shore, Jay Sanford

Issue Date

1993

Doctoral Committee Chair(s)

Oldfield, E.,

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Chemistry, Inorganic
• Chemistry, Physical
• Physics, Condensed Matter

Abstract

• A series of oxide superconductors and related compounds, including: BaPbO$\sb3,$ BaBiO$\sb3,$ BaSb$\sb{0.25}$Pb$\sb{0.75}$O$\sb3,$ BaBi$\sb{0.25}$Pb$\sb{0.75}$O$\sb3,$ Ba$\sb{0.6}$K$\sb{0.4}$BiO$\sb3,$ Bi$\sb2$Sr$\sb2$CuO$\sb{\rm 6 + x},$ La$\sb{1.85}$Ca$\sb{0.15}$CuO$\sb{\rm 4-x},$ La$\sb{1.85}$Sr$\sb{0.15}$CuO$\sb{\rm 4-x},$ Bi$\sb2$Sr$\sb2$CaCu$\sb2$O$\sb{\rm 8 + x},$ YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x},$ and Tl$\sb2$Ba$\sb2$CaCu$\sb2$O$\sb{\rm 8 + x},$ were studied using solid state $\sp $O and $\sp{135,137}$Ba nuclear magnetic resonance (NMR) spectroscopy. The measurements are related to the compounds' atomic, electronic and magnetic structures. The $\sp $O NMR results indicate that most of the oxide superconductors are inhomogeneous, and have longitudinal relaxation mechanisms that are magnetic in origin. Variable temperature measurements of the bismuthate and plumbate materials are consistent with the relaxation being dominated by the oxygen 2p character of the conduction band. While similar measurements of the CuO$\sb2$ 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$\sb{\rm c},$ consistent with a relation derived from the Bardeen-Cooper-Scheifer (BCS) theory of superconductivity. The relaxation rates of the cuprates are fairly constant (T$\sb1$T $\approx$ 3.9 $\pm$ 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, it is determined that the copper spin fluctuations are localized near the reciprocal lattice vector ($\pi$/a,$\pi$/a).
• From $\sp{135,137}$Ba NMR and NQR measurements of YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x},$ 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$\sb2$ planar spin fluctuations.

Graduation Semester

1993

Type of Resource

text

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