共查询到20条相似文献,搜索用时 15 毫秒
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P. Boolchand D. McDaniel C. Blue Y. Wu R. Enzweiler K. Elgaid R. Burrows 《Hyperfine Interactions》1992,68(1-4):15-25
A new symmetric Fe3+ site (labelled E) (δ=0.28(2) mm/s and Δ=0.15 mm/s) is observed in the R1Ba2Cu3O7 family of superconductors for R=Y and Eu. The decay and growth of site E are established in two seemingly unrelated experiments,
one as a function of room temperature aging for R=Y, and the other as a function of oxygen loading at elevated temperatures
and pressures for R=Eu. In each experiment, the results show that site E is genetically related to the well documented chainsites
A(Δ=1.9 mm/s), C(Δ=1.1 mm/s) and D(Δ=1.6 mm/s). We propose that site E represents a quasi-octahedral chain-site having pairs
of O(1), O(4) and O(5) nearestneighbor oxygen sites. The two remaining doublets, B(Δ≈0.4 mm/s) and B′(Δ=0.78 mm/s) represent
Fe3+ dopant sites present in the all-important CuO2 planes, possessing coordination numbers of 6 and 5, respectively. 相似文献
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Flux flow was studied over an entire temperature range down to T approximately 2% of T(c) by using intense pulsed current densities to overcome flux-vortex pinning. The resistivity at high vortex velocities is proportional to B and roughly follows rho approximately rho(n)B/H(c2), with a prefactor of order unity. Contrary to some speculation, rho(n) saturates to a finite residual value as T-->0, indicating a metallic (rho-->finite) rather than insulating (rho-->infinity) normal state, and the vortex dissipation continues to be conventional as T-->0. 相似文献
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M. Ausloos F. Gillet Ch. Laurent P. Clippe 《Zeitschrift für Physik B Condensed Matter》1991,84(1):13-16
We have examined the deviation from linearity of the temperature dependence of the electrical resistivity of a YBaCuO ceramics. We have observed at high temprature a crossover behavior toward a logarithmic temperature dependence at lower temperature. It seems relevant to attribute the origin of such a term to a pair breaking mechanism contribution, thus to give a lower bound to the existence of superconductivity fluctuations onset temperature. Our findings also implies that carriers are bosons aboveT
c
. 相似文献
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In this paper the kinetics of oxygen desorption from Y Ba2Cu3O7-δ has been investigated and measurements carried out in the temperature range 350–750 C. It is shown that the oxygen desorption
is diffusion-controlled (and not surface-controlled), and characteristic of diffusion from small grains in a loosely coupled
porous matrix. At every temperature a number of time constants with well-defined ratios appear and have been identified and
measured. These time constants can be related to the average bulk diffusion constant which shows an Arrhenius behaviour with
deviations around 750°C which are ascribed to the well-known orthorhombic to tetragonal transition. In this paper we establish
the basic underlying physical mechanism of oxygen desorption in Y Ba2Cu3O7-δ. 相似文献
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Summary Evidence is given that in Y1−Ba2−Cu3−O7 single crystals a critical state is developed on increasing (or decreasing) the applied fieldH
0, only whenH
0 is parallel to the crystalc-axis. An ?irreversibility? line in the (H, T)-plane can be drawn where the irreversibility of the second-harmonic response sets in.
In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching. 相似文献
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In this paper we report measurements of the thermoelectric power on a series of Y1Ba2Cu3O7-x specimens with varying amounts of oxygen deficiency obtained by changing the cooling rate of the sintered specimens. The
specimens have been characterized by X-ray diffraction measurements, electric resistivity and oxygen contents. The temperature
variation of the thermopower reveals a peak just before the onset of superconducting transition. We examine possible theoretical
explanations of this anomaly. In particular we argue that this anomaly is associated with the pairing fluctuations in the
normal state close toT
c
. We present some theoretical results in support of this conclusion. 相似文献
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Shengyun Zhu Shennan Zheng Anli Li Hangchen Huang Hongshan Du Honglin Din Donghong Li 《Hyperfine Interactions》1990,62(3):213-218
HighT
c superconductivity in the YBaCuO superconductor has been investigated through the quadrupole interaction of the probe nuclei99Tc. The quadrupole interactions were measured by the TDPAC method from 77 to 296 K. The probe nuclei99Tc were introduced into the YBaCuO superconducting specimen by diffusion. The derived electric quadrupole interaction parameters
show that the probe nuclei are subject to a unique EFG interaction and occupy a substitutional lattice site in the YBaCuO
superconductor. A strong EFG of 1019 V/cm2 was observed. The temperature dependence of the EFG exhibits a linear decrease with temperature increase. Anomalies of both
EFG and ν were found in the superconducting transition temperature region. The role of the oxygen vacancies in the Cu−O chains
is discussed. 相似文献
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Positron lifetime and Doppler broadened annihilation radiation lineshape measurements have been carried out in Y1Ba2Cu3O7−x
as a function of temperature in the range of 300 K to 58 K. The positron lifetime and the peak parameter of the annihilation
radiation lineshape are observed to decrease on lowering the temperature without showing any discontinuous change across the
superconducting transition temperature of 90 K as determined by susceptibility measurements. The variation of positron annihilation
parameters with temperature in the superconducting state is significantly larger than that in the normal state. This is qualitatively
explained in terms of the dimerization of oxygen ions in the superconducting state of Y1Ba2Cu3O7−x
. 相似文献