Microscopic study of local structure and charge distribution in metallic La{sub 2}CuO{sub 4+{delta}}

Conference · Fri Oct 29 04:00:00 EDT 1993

OSTI ID:10107491

Hammel, P C; Reyes, A P; Ahrens, E T; Fisk, Z; Canfield, P C; Thompson, J D ^[1]; Schirber, J E ^[2]

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1. Los Alamos National Lab., NM (United States)
2. Sandia National Labs., Albuquerque, NM (United States)

The authors employ NMR and NQR spectroscopy as probes of local structure and charge environments in metallic La{sub 2}CuO{sub 4+{delta}} ({Tc} = 38 K). They discuss the effect of annealing the sample at various temperatures T{sub a} ({Tc} < T{sub a} < 300K) on the superconducting {Tc}. The dependence of {Tc} on annealing indicates that annealing allows the development of structural order which is important for {Tc}. The {sup 139}La quadrupole frequency, {nu}{sub Q} is smaller than in undoped materials. This is unexpected and may indicate a smaller charge on the apex oxygen in the doped material and thus a different distribution of charge between the La-O layer to the planes. The further, rapid decrease in {nu}{sub Q} just above {Tc} indicates that temperature dependent charge redistribution is occurring. The presence of doped holes induces a distribution of displacements of the apex oxygen off of the vertical La-Cu bond axis. These vary from zero to the value observed in lightly doped (antiferromagnetic) La{sub 2}CuO{sub 4+{delta}}. These measurements demonstrate a striking degree of inhomogeneity in the crystal structure of the La-O layer. Copper NQR spectroscopy shows that there are two distinct copper sites in the CuO{sub 2} planes and thus that either the structure or the charge distribution in the planes is inhomogeneous as well. These inhomogeneities are the intrinsic response of the crystal to doped holes; they are not the result of distortions of the lattice due to the presence of interstitial oxygen atoms.

• Research Organization: Sandia National Labs., Albuquerque, NM (United States); Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 10107491
• Report Number(s): SAND--93-2709C; LA-UR--93-3836; CONF-9309283--2; ON: DE94003801
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202
360204
ANNEALING
CHARGE DISTRIBUTION
COPPER OXIDES
CRYSTAL STRUCTURE
HOLES
LANTHANUM OXIDES
NUCLEAR MAGNETIC RESONANCE
NUCLEAR QUADRUPOLE RESONANCE
PHYSICAL PROPERTIES
STRUCTURE AND PHASE STUDIES
TRANSITION TEMPERATURE