Thermal conductivity of YBa 2 Cu 3 O 7 from 7 K to 260 K
TL;DR: In this paper, thermal conductivity of YBa2Cu3O7 was measured on samples of a few mm thickness and the experimental set up was described and results discussed, pointing towards a contribution to thermal resistivity from three-phonon Umklapp processes.
Abstract: Thermal conductivity of YBa2Cu3O7 has been measured on samples of a few mm thickness. AboveT
c thermal conductivity is found to decrease with increase in temperature, pointing towards a contribution to thermal resistivity from three-phonon Umklapp processes. BelowT
c thermal conductivity increases rapidly before reaching a maximum at about 50 K and then falls towards zero at lower temperatures. The experimental set up is described and results discussed.
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TL;DR: In this paper, the relative magnitude of the carrier and the phonon contributions to total thermal conductivity was estimated, and the slope of lattice thermal conductivities at TC was further calculated.
Abstract: Thermal conductivities of a number of vanadium and nickel substituted 2223 (BiPb) superconducting cuprates are reported between 10 and 150K. Substitution of both vanadium and nickel in (BiPb) system influence strongly the magnitude of thermal conductivity (K) of the pellets, both above and below Tc. The reduced temperature derivative of the normalised conductivity ( K S K N ) for the reported samples varies between −0.78 and −1.32. Evoking Wiedemann - Franz law the relative magnitude of the carrier and the phonon contributions to total K was estimated. Analysis of KL data using Tewordt-Wolkhausen expression indicates that for all the samples phonon-defect scattering dominates above Tc. We further calculate the slope of lattice thermal conductivity at TC and estimate that the slope of carrier thermal conductivity is very large (>8), which indicates strong coupling for some of the carriers in these systems.
15 citations
TL;DR: In this paper, the superconducting Nd(Ba,Nd)2.1Cu3O7−δ system has been prepared using conventional solid-state reaction technique.
Abstract: In this study, the superconducting Nd(Ba,Nd)2.1Cu3O7−δ system has been prepared using conventional solid-state reaction technique. Transport properties including structural/microstructural evolution, electrical, magnetic and critical current density properties were investigated. After high temperature heat treatments at over 1,000 °C, large and strongly connected grains were obtained but weakly connected and small in size granular formation were obtained for the low temperature heat treated samples at around 900 °C. The best T
c
and T
0
values were obtained as 93 and 89 K respectively for the sample prepared at 1,020 °C for 24 h, which is very close to peritectic temperature of YBCO material. Magnetization of the sample heat treated at 1,020 °C was investigated in detail. The magnetization hysteresis loops are expounded to be the product of Nd-123 grains and unscreened Nd3+ ions within intergranular boundaries and vortex cores. The peak effect on the magnetization curves was described by the extended critical state model. Temperature dependencies of the irreversibility field, the peak field and the full penetration field correlate and there is scaling behavior of the pinning force as well. Thermoelectric power data was analyzed by “Modified two band model with linear T-term for superconductors”. Temperature dependence of thermal conductivity of the samples showed small peak with broad maximum just below the T
c value. Thermal conductivity of samples prepared was calculated by using “The Modified Callaway Model and Wiedermann–Franz law” and results obtained discussed.
14 citations
TL;DR: In this paper, a model of the dependence of the electrical conductivity upon mechanical deformation during field-cooling magnetization is proposed, which is carried out by the critical current density as a function of induced thermal and mechanical strain in the bulk.
Abstract: Most of the latest models of HTS bulk magnetization take into account the thermal and electromagnetic coupling, but, they still lack the implementation of the mechanical deformation under strong magnetic fields. The following work tries to fill up partly the gap by proposing a model of the dependence of the electrical conductivity upon mechanical deformation during field-cooling magnetization. This dependence is carried out by the critical current density as a function of induced thermal and mechanical strain in the bulk. As a first approximation and bearing in mind the obvious discrepancies, a simple model inferred from HTS thin films and generic knowledge on ceramics is proposed. This first approach allows drawing some generalities on the expected thermal, magnetic, and mechanical response of disk-shaped YBCO pellets during magnetization. The utter goal is to assess design parameters to insert those pellets in electrical rotatory machines.
7 citations
Cites result from "Thermal conductivity of YBa 2 Cu 3 ..."
...were fitted from averaged results found in [19]–[22]....
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TL;DR: In this paper, the electrical and thermal transport properties such as thermoelectric power and thermal conductivity of the Se added YBCO system was investigated, and the results indicated that hole type conductivity indicates the hole type this paper.
Abstract: In this study, the electrical and thermal transport properties such as thermoelectric power and thermal conductivity of the Se added YBCO system was investigated. The samples fabricated under different heat treatment conditions exhibited the T c value between 90.1 K and 80.6 K. Positive thermoelectric power for all the samples was obtained over all measurement temperature range which indicates the hole type conductivity. Thermoelectric power data was analyzed by replacing term ( T – T * ) by T in “ Modified two band model with linear T-term ” which is good agreement with experimental TEP data for all the samples. T * obtained by fitting corresponds to a temperature close to T 0 obtained from resistivity measurement. Temperature dependence of thermal conductivity of the samples showed small peak with broad maximum just below T c . Thermal conductivity of the samples prepared was analyzed by the lattice thermal conductivity component by “ The modified Callaway model ” and the electronic component by “ Wiedemann –Franz law ”.
6 citations
TL;DR: In this article, the role of both electrons and phonons in the origin of thermal conductivity of a set of (Bi0.8Pb0.2Sr2Ca2Cu3O10+δ) pellets in the temperature range between 10 and 150 K is reported.
Abstract: Thermal conductivity of a set of (Bi0.8Pb0.2−y
V
y
)2Sr2Ca2Cu3O10+δ (0 =y ≤ 0.05) pellets in the temperature range between 10 and 150 K is reported. Vanadium substitution influences strongly the magnitude of thermal conductivity (λ,) over the entire temperature range. But the nature of λ(T) dependence remains similar to that generally observed for HTSCs. The electronic contribution to the total λ in the normal state is estimated to be ∼ 25%. We have attempted to examine our data, assuming the role of both electrons and phonons in the origin of the λ(T) behaviour belowT
c. Observed temperature variation of λ(T) for the present set of samples could be explained very well assuming this electron + approach. Some of the microscopic quantities estimated from the best-fit parameters give reasonable values.
4 citations
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TL;DR: In this article, a theory of the thermal conductivity of superconductors is presented, based on the theory of super conductivity due to Bardeen, Cooper, and Schrieffer, which is treated as quasi-particles, allowing a Boltzmann equation to be set up.
Abstract: A theory of the thermal conductivity of superconductors is presented, based on the theory of superconductivity due to Bardeen, Cooper, and Schrieffer. The excited states of the system are treated as quasi-particles, allowing a Boltzmann equation to be set up. The electronic contribution to the thermal conductivity when the dominant scatterers are impurities has been calculated exactly. The result is very close to that of the Heisenberg-Koppe theory which is in fair agreement with experiment. The variational principle of Wilson has been used to find the electronic conductivity when the dominant scatterers are lattice waves. It is concluded that the theory fails to predict the sharp drop in the ratio $\frac{{\ensuremath{\kappa}}_{\mathrm{es}}}{{\ensuremath{\kappa}}_{\mathrm{en}}}$ as the temperature is lowered below ${T}_{c}$, a feature which is characteristic of the experimental results. The effect of the electrons on the lattice conductivity has also been calculated. The theoretical values may be too large.
362 citations
TL;DR: In this paper, the contribution of longitudinal acoustic phonons to the electron-phonon coupling constant λ was estimated to lie within the weak coupling range, taking into account scattering of phonons by structural defects like boundaries, point defects, and sheetlike faults.
Abstract: The observed peak below T c in the thermal conductivity К of YBa 2 Cu 3 O 7 can be explained fairly well by applying the BCS theory for lattice thermal conductivity limited by electron scattering. The contribution of longitudinal acoustic phonons to the electron-phonon coupling constant λ is estimated to lie within the weak coupling range. In addition to phonon-electron scattering we have taken into account scattering of phonons by structural defects like boundaries, point defects, and sheetlike faults. More detailed information about the strength of the phonon-electron scattering and the nature of the gap (weak or strong coupling) could be obtained from measurements of the anisotropy of К in single crystals.
155 citations
TL;DR: In this article, the authors measured the thermal conductivity, thermopower, Hall constant, and resistivity of a Y${T}_{c}$ superconductor, and ascribe to an increase in lattice conduction due to a reduction in the scattering of phonons by holes.
Abstract: We have measured the thermal conductivity, thermopower, Hall constant, and resistivity of a Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ high-${T}_{c}$ superconductor. The thermal conductivity shows a striking increase below the transition temperature ${T}_{c}$, which we ascribe to an increase in lattice conduction due to a reduction in the scattering of phonons by holes as superconducting pairs form. This property, and the others we have measured, are consistent with ordinary metallic conduction mechanisms with short phonon and carrier free paths, and a strong interaction of phonons with a small density of hole carriers.
154 citations
TL;DR: In this paper, a review of existing data on the thermal conductivity of high-T====== c¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ c¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ superconductors is presented, including pristine polycrystalline high-t====== c¯¯ ceramics, single crystal specimens, and materials structurally modified by substitution or by radiation damage.
Abstract: This paper reviews existing data on the thermal conductivity of high-T
c
superconductors. Included are discussions of pristine polycrystalline high-T
c ceramics, single crystal specimens, and high-T
c
materials structurally modified by substitution or by radiation damage. The thermal conductivity of high-T
c
superconductors is compared with that of conventional superconductors, and dramatic differences are found between the two families. Mechanisms of thermal conductivity applicable to high-T
c
perovskites are discussed and implications for theories of high-T
c
superconductivity are noted.
123 citations
TL;DR: In this article, the Hall coefficient is shown to vary with T-1.2 K ≤ T ≤ 120 K. The thermopower is very small and sample dependent, and the thermal conductivity indicates dominant phonon heat transport in more than one band.
Abstract: For the high-Tc superconductor YBa2Cu3O7, we present results on the resistivity, Hall effect, and thermopower for temperatures up to 350 K as well as on the thermal conductivity in the range 0.2 K ≤ T ≤ 120 K. The Hall coefficient is positive and varies approximately with T-1. The thermopower is very small and sample dependent. These results suggest transport in more than one band. The thermal conductivity indicates dominant phonon heat transport. For the residual resistivity an upper bound, ρ0 ≤ 250 μΩ cm, is deduced. Combining this with published results for the slope of the upper critical field and the penetration depth, we estimate the specific-heat coefficient, 5 ≤ γ < 9 mJ/K2 mole-Cu, and the effective carrier density, 1.1 1022 cm-3.
73 citations