176 research outputs found
ab-plane resistivity and possible charge stripe ordering in strongly underdoped LaSrCuO single crystals
We have measured the ab-plane resistivity of LaSrCuO single
crystals with small Sr content (x=0.052 0.075) between 4.2 and 300 K by
using the AC Van der Pauw technique. As recently suggested by Ichikawa et al.,
the deviation from the linearity of the curve starting
at a temperature T can be interpreted as due to a progressive
slowing down of the fluctuations of pre-formed charge stripes. An electronic
transition of the stripes to a more ordered phase could instead be responsible
for some very sharp anomalies present in the of
superconducting samples just above .Comment: M2S-HTSC-VI Conference paper (2 pages, 2 figures), using Elsevier
style espcrc2.st
Strain Effects on Point Defects and Chain-Oxygen Order-Disorder Transition in 123-Structure Cuprate Superconductors
The energetics of Schottky defects in 123 cuprate superconductor series, (where RE = lanthandies) and (AE =
alkali-earths), were found to have unusual relations if one considers only the
volumetric strain. Our calculations reveal the effect of non-uniform changes of
interatomic distances within the RE-123 structures, introduced by doping
homovalent elements, on the Schottky defect formation energy. The energy of
formation of Frenkel Pair defects, which is an elementary disordering event, in
123 compounds can be substantially altered under both stress and chemical
doping. Scaling the oxygen-oxygen short-range repulsive parameter using the
calculated formation energy of Frenkel pair defects, the transition temperature
between orthorhombic and tetragonal phases is computed by quasi-chemical
approximations (QCA). The theoretical results illustrate the same trend as the
experimental measurements in that the larger the ionic radius of RE, the lower
the orthorhombic/tetragonal phase transition temperature. This study provides
strong evidence of the strain effects on order-disorder transition due to
oxygens in the CuO chain sites.Comment: In print Phys Rev B (2004
Cu Nuclear Quadrupole Resonance Study of Site-Disorder and Chemical Pressure Effects on Y(Ba1-xSrx)2Cu4O8
We report a zero-field Cu nuclear quadrupole resonance (NQR) study on the
effects of nonmagnetic Sr substitution for high-Tc superconductors,
Y(Ba1-xSrx)2Cu4O8 (Tc=82-80 K for x=0-0.4), using a spin-echo technique. The
site-disordering and chemical pressure effects associated with doping Sr were
observed in the broadened, shifted Cu NQR spectra. Nevertheless, the site
disorder did not significantly affect the homogeneity of Cu electron spin
dynamics, in contrast to the in-plane impurity. The peak shift of Cu NQR
spectrum due to Sr was different between the chain- and the plane-Cu sites,
more remarkably than those under a hydrostatic physical pressure, suggesting
anisotropic or nonuniform local structural strains. The small decrease of Tc
due to Sr can be traced back to either a cancellation effect on Tc between the
disorder and the pressure, or an anisotropic or nonuniform chemical pressure
effect on Tc.Comment: 4 pages, 5 figure
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Rietveld refinement of YBa{sub 2}Cu{sub 3-x}Ni{sub x}O{sub y} prepared by quenching and oxygen gettering
We have refined the structures for YBa{sub 2}Cu{sub 2.94}Ni{sub 0.06}O{sub y} (2% Ni) and YBa{sub 2}Cu{sub 2.80}Ni{sub 0.20}O{sub y} (6.67% Ni) at y {approximately} 6.95 and y {approximately} 6.5 contents. Oxygen was reduced by two independent methods: quenching from 690{degrees}C and oxygen gettering at 450{degrees}C. Cu-0 bond lengths were calculated based on Rietveld structure refinements for the various samples; they indicate the likely occupancy of Ni in the plane (Cu2) site of the 123 superconductor
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