Anomalous thermoelectric power of the Mg 1− x Al x B 2 system with x = 0.0–1.0 (original) (raw)
Related papers
Thermal conductivity of single-crystalline MgB_{2}
Physical Review B, 2002
The ab-plane thermal conductivity κ of single-crystalline hexagonal MgB2 has been measured as a function of magnetic field H with orientations both parallel and perpendicular to the c-axis and at temperatures between 0.5 and 300 K. In the mixed state, κ(H) measured at constant temperatures reveals features that are not typical for common type-II superconductors. The observed behavior may be associated with the field-induced reduction of two superconducting energy gaps, significantly different in magnitude. A nonlinear temperature dependence of the electronic thermal conductivity is observed in the field-induced normal state at low temperatures. This behavior is at variance with the law of Wiedemann and Franz, and suggests an unexpected instability of the electronic subsystem in the normal state at T ≈ 1 K. 74.25.Fy,
Physical Review B, 2006
We report data on the thermal conductivity ͑T , H͒ along the basal plane of the hexagonal crystal structure of superconducting Mg 1−y Al y B 2 with y = 0.02 and 0.07 at temperatures between 0.5 and 50 K and in external magnetic fields between 0 and 70 kOe. The substitution of Al for Mg leads to a substantial reduction of the heat transport via electronic quasiparticles. The analysis of the ͑T , H͒ data implies that the Al impurities provoke an enhancement of the intraband scattering rate, almost equal in magnitude for both the and the bands of electronic excitations. This is in contrast with conclusions drawn from analogous data sets for material in which carbon replaces boron and where mainly the intraband scattering rate of the band is enhanced. Our complete data set, including additional results of measurements of the low-temperature thermal conductivity of pure MgB 2 , confirms the validity of the Wiedemann-Franz law for both pure and doped MgB 2 .
Thermal conductivity of MgB2 in the superconducting state
Physical Review B, 2003
We present thermal conductivity measurements on very pure and dense bulk samples, as indicated by residual resistivity values as low as 0.5 mW cm and thermal conductivity values higher than 200 W/mK. In the normal state we found that the Wiedemann Franz law, in its generalized form, works well suggesting that phonons do not contribute to the heat transport. The thermal conductivity in the superconducting state has been analysed by using a two-gap model. Thank to the large gap anisotropy we were able to evaluate quantitatively intraband scattering relaxation times of pi\pi pi and sigma\sigma sigma bands, which depend on the disorder in different way; namely, as the disorder increases, it reduces more effectively the relaxation times of pi\pi pi than of sigma\sigma sigma bands, as suggested by a recent calculation [1].
Thermal conductivity of superconducting MgB2
2001
Thermal conductivity of superconducting MgB2 was studied in both the superconducting and the normal state region. The latter is almost equally determined by the electronic - and the lattice contribution to the total thermal conductivity. In the superconducting state, however, the lattice contribution is larger. The electronic thermal conductivity below Tc was derived from the experimental data considering the Bardeen-Rickayzen-Tewordt theory together with the model of Geilikman. The analysis shows that electron scattering on static imperfections dominates.
Thermoelectric power studies on Nd1.82−xSrxCe0.18CuOy:x≤0.18 superconductors
Journal of Applied Physics, 1996
Chemical pressure and electron doping effects in SrPd2Ge2 single crystals J. Appl. Phys. 111, 07E117 Fluctuation-induced conductivity analyses of Be-doped (Bi0.25Cu0.25Li0.25Tl0.25)Ba2Ca2Cu3O10-δ superconductors in the critical regime and beyond J. Appl. Phys. 111, 033917 (2012) Enhancement of the upper critical field in codoped iron-arsenic high-temperature superconductors Thermoelectric power (S) studies on a Nd 1.82Ϫx Sr x Ce 0.18 CuO y :xр0.18 superconducting system in the temperature range 35-250 K are reported here. In the xϭ0.09 sample, synthesized in the reduced environment, the small magnitude of S is highly metalliclike and its sign is negative, a characteristic of electron conduction. The sign of S for the xϭ0.18 sample shows a crossover below 75 K from negative to positive, in apparent conflict with electronic conduction. Interestingly, after oxygenation this sample exhibits a broadened but positive phonon draglike peak. This oxygenated sample shows overcompensation of the carrier ͑electron͒ concentration. Critical analysis of the data suggests that Sr doping seemingly causes a competition between electron-and holelike conduction. The slope dS/dT is, in general, negative suggesting that the main contribution is coming from the diffusive part. The observed thermopower features seem to fall in line with the theoretical curves of Durczewski and Ausloos ͓Z. Phys. B 85, 59 ͑1991͒; Phys. Rev. B 53, 1762 ͑1996͔͒ based on the inelastic scattering of quasifree electrons by phonons.
Ab initio thermal conductivity of thermoelectric Mg 3 Sb 2 : Evidence for dominant extrinsic effects
The lattice thermal conductivity of the candidate thermoelectric material Mg 3 Sb 2 is studied from first principles, with the inclusion of anharmonic, isotope, and boundary scattering processes, and via an accurate solution of the Boltzmann equation. We find that the anomalously low observed conductivity is due to grainboundary scattering of phonons, whereas the purely anharmonic conductivity is an order of magnitude larger. Mass disorder due to alloying and off-stoichiometry is also found to contribute significantly to its decrease. Combining ab initio values vs sample size with measured grain-size distributions, we obtain an estimate of κ vs T in nanopolycrystalline material in good agreement with typical experiments, and compute the ZT figure of merit in the various cases.
Thermoelectric power of magnetic metals
Journal of Magnetism and Magnetic Materials, 1985
We present a theory of the thermoelectric power tensor of anisotropic ferromagnetic metals with localized magnetic moments starting from the Boltzmann equation and incorporating anisotropy effects due to the lattice structure through a parameter measuring the anisotropy in the sound velocity. Elastic and inelastic phonon and spin scattering contributions are taken into account through a linear superposition of scattering cross sections. A mean field approximation is used to describe the ordered magnetic phase. Spin wave and impurity scattering, phonon and magnon drag are not included. In a range encompassing the Curie temperature, i.e. at "moderate temperatures", the theory quantitatively reproduces observed features except for specific details (e.g. rounding near T,) needing other physical input. We compare our theory to data on single crystals of Gd and Tb,,Gd,,.
Strong electron-phonon coupling in superconducting MgB 2 : A specific heat study
Physical Review B, 2001
We report on measurements of the specific heat of the recently discovered superconductor MgB2 in the temperature range between 3 and 220 K. Based on a modified Debye-Einstein model, we have achieved a rather accurate account of the lattice contribution to the specific heat, which allows us to separate the electronic contribution from the total measured specific heat. From our result for the electronic specific heat, we estimate the electron-phonon coupling constant λ to be of the order of 2, significantly enhanced compared to common weak-coupling values ≤ 0.4. Our data also indicate that the electronic specific heat in the superconducting state of MgB2 can be accounted for by a conventional, s-wave type 74.25.Kc The recent discovery of superconductivity in MgB 2 below T c ≈ 39 K [1] has caused a remarkable excitement in the solid-state physics community. Critical temperatures of this magnitude inevitably raise the question whether mechanisms other than the common electron-phonon interaction are responsible for the transition. In their very recent work, Bud'ko et al.
Ultra-low lattice thermal conductivity of MgPb$_2$Te -- A first principles study
2021
Thermoelectric technology is an alternate way to efficiently utilize the energy by converting waste heat into electricity. Thermoelectric requires material with low thermal conductivity to improves its thermoelectric performance. In this work, by solving Boltzmann transport equation based on first principles calculations, we report an ultra-low room temperature thermal conductivity of 2.08 Wm-1K-1 and 2.9 Wm-1K-1 along c-axis and a-axis respectively for pure MgPb2Te. To explain this ultra-low thermal conductivity, we analyzed the elastic constants, phonon group velocity, phonon-phonon scattering and contribution from transverse acoustic, longitudinal acoustic and optical phonon branches. We also report the thermal conductivity of MgPb2Te nanostructures. At 50 nm, the room temperature thermal conductivity of MgPb2Te is 0.957 Wm-1K-1 and 1.459 Wm-1K-1 along c-axis and a-axis respectively. Ultra-low thermal conductivity unraveled in this work shows MgPb2Te would a promising material fo...