# Ageing effects on thermal conductivity of YBa2Cu3O7−y

TL;DR: In this article, a modified BRT type analysis points to an increase in point defects and planar defects in YBa 2 Cu 3 O 7−y (YBCO) samples.

Abstract: Significant reduction in the magnitude of thermal conductivity of a sample of YBa 2 Cu 3 O 7−y (YBCO) has been observed when the sample was stored in dry air for a period of one year, though it was reoxygenated to restore superconductivity. A modified BRT type analysis points to an increase in point defects and planar defects.

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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

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TL;DR: A mean-field model is fit to the experimental data, and suggests that the second type of diagram is correct, and the variation of the oxygen partial pressure with delta and t is discussed.

Abstract: The superconducting oxide YBa/sub 2/Cu/sub 3/O/sub 6+//sub delta/ is found in two structures: a tetragonal structure (T) that is stoichiometric when delta = 0, and an orthorhombic (O) structure stoichiometric when delta = 1 Assuming that only these phases appear in the phase diagram of the oxide as temperature (t) and delta are varied, it is shown that the phase diagram must have one of two relatively simple forms The first has a T field at high t and low delta, an O field at lower temperature and high delta, and a T+O two-phase field that separates the two at low t The second has these features, and also includes an O+O' two-phase field that results from a miscibility gap in the O phase A mean-field model is fit to the experimental data, and suggests that the second type of diagram is correct The calculated phase diagram is presented The variation of the oxygen partial pressure with delta and t is also discussed

75 citations

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TL;DR: In this paper, a systematic study of the ab-plane thermal conductivity on single crystal and liquid-phase processed (LPP) specimens of YBa 2 Cu 3 O 7−δ (δ≤0.16) in the temperature range 10 K≤ T ≤300 K was performed.

Abstract: We report a systematic study of the ab -plane thermal conductivity (κ) on single crystal and liquid-phase processed (LPP) specimens of YBa 2 Cu 3 O 7−δ (δ≤0.16) in the temperature range 10 K≤ T ≤300 K. From measurements of electrical conductivity on the same specimens and application of the Wiedemann-Franz law we estimate the relative contributions to the heat conduction from the carriers and the lattice. The normal-state phonon scattering mechanisms are quantified by calculations which employ the conventional theory of lattice heat conduction by longitudinal acoustic phonons. Differences in the magnitude and temperature dependence of κ for the LPP and crystal specimens are accounted for by differences in the relative weight of phonon-defect, phonon-carrier, and phonon-phonon scattering. For all specimens phonon-defect scattering predominates throughout most of the temperature range.

27 citations

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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.

10 citations