Normal-state electrical resistivity of Chevrel-phase superconductors of the type Cu1.8Mo6S8-ySey, 0⩽y⩽8

TL;DR: In this paper, normal state electrical resistivity data from 12-300k on Chevrel phase superconductors of the type Cu1.8Mo6S8-ySey, 0

Abstract: Normal-state electrical resistivity data from 12-300K on Chevrel-phase superconductors of the type Cu1.8Mo6S8-ySey, 0

TL;DR: Chevrel phases have a long and incredible past as outstanding materials for basic and applied research but, in addn. to that, they have a bright future ahead because of a large range of potentialities.

Abstract: The ternary molybdenum chalcogenides MxMo6X8 (X = chalcogen), known as Chevrel phases, constitute an outstanding family of materials presenting numerous and spectacular properties. More than 100 examples of these compds. have been synthesized thanks to their versatile crystal structure. Numerous variants are found, from the binary material formed just by the molybdenum clusters Mo6X8 leaving a three-dimensional lattice where the third element M can be inserted, up to a condensation of clusters giving rise to a monodimensional material. The great interest in these compds., discovered more than 40 years ago, came from their superconducting crit. temp. and upper crit. fields (15 K for the former, 50 T at 4.2 K for the latter), both being reasonably high values at the time of their discovery thus opening enormous hopes for their use in the fabrication of magnets. Other fundamental features are found, such as the coexistence of magnetic order with the superconducting state. These features are still of interest for the scientific community, but other potential applications are now foreseen, such as their use in batteries, catalysis and thermopower technol.We recall herein some basic characteristic of Chevrel-phases, mentioning several important families, their crystal structure and mode of elaboration. This contribution being focused on the superconducting properties, we put an accent on some fundamental aspects, such as the structural and electronic transitions, the vortex lattice, their granular behavior, crit. current densities, upper field and anisotropy, to finally discuss the so-called unconventional supercond., classifying these materials among the "exotic superconductors" and making a parallel with other superconductors which, in spite of their quite different electronic and crystal structures, present similar features.Chevrel phases have a long and incredible past as outstanding materials for basic and applied research but, in addn. to that, they have a bright future ahead because of a large range of potentialities.

TL;DR: The thermoelectric power of Chevrel-phase superconductors of the type Cu18Mo6S8-ySey, 0

Abstract: The thermoelectric power, S, of Chevrel-phase superconductors of the type Cu18Mo6S8-ySey, 0

TL;DR: In this paper, the authors investigated the enhanced superconductivity with the help of experimental studies of the temperature dependent electrical resistivity (ρ(T)) and heat capacity (CP(T)), as well as the theoretical estimation of electronic density of states (DOS) using band structure calculations.

Abstract: Superconducting transition temperature TC of some of the cubic β phase Rex alloys with is an order of magnitude higher than that in the elements Mo and Re. We investigate this rather enigmatic issue of the enhanced superconductivity with the help of experimental studies of the temperature dependent electrical resistivity (ρ(T)) and heat capacity (CP(T)), as well as the theoretical estimation of electronic density of states (DOS) using band structure calculations. The ρ(T) in the normal state of the Rex alloys with is distinctly different from that of Mo and the alloys with We have also observed that the Sommerfeld coefficient of electronic heat capacity γ, superconducting transition temperature TC and the DOS at the Fermi level show an abrupt change above . The analysis of these results indicates that the value of electron–phonon coupling constant λep required to explain the TC of the alloys with is much higher than that estimated from γ. On the other hand the analysis of the results of the ρ(T) reveals the presence of phonon assisted inter-band s–d scattering in this composition range. We argue that a strong electron–phonon coupling arising due to the multiband effects is responsible for the enhanced TC in the β phase Rex alloys with .

TL;DR: In this article, the authors investigated the effect of electron-phonon coupling on the superconducting transition temperature of some of the cubic Mo$1-x}$Re$_x$ alloys with x > 0.10.

Abstract: Superconducting transition temperature $T_C$ of some of the cubic $\beta$-phase Mo$_{1-x}$Re$_x$ alloys with x > 0.10 is an order of magnitude higher than that in the elements Mo and Re. We investigate this rather enigmatic issue of the enhanced superconductivity with the help of experimental studies of the temperature dependent electrical resistivity ($\rho$(T)) and heat capacity (C$_P$(T)), as well as the theoretical estimation of electronic density of states (DOS) using band structure calculations. The $\rho$(T) in the normal state of the Mo$_{1-x}$Re$_x$ alloys with x > 0.15 is distinctly different from that of Mo and the alloys with x 0.10. The analysis of these results indicates that the value of electron-phonon coupling constant {\lambda}ep required to explain the $T_C$ of the alloys with x > 0.10 is much higher than that estimated from $\gamma$. On the other hand the analysis of the results of the $\rho$(T) reveals the presence of phonon assisted inter-band s-d scattering in this composition range. We argue that a strong electron-phonon coupling arising due to the multiband effects is responsible for the enhanced $T_C$ in the $\beta$-phase Mo$_{1-x}$Re$_x$ alloys with x > 0.10.

TL;DR: In this paper, a simple model for the 3D strain dependence of the critical current density in ITER Nb3Sn strands is proposed based on the strain-induced variation in the electronic density of states at the Fermi surface.

Abstract: The critical current density parameterization for the International Thermonuclear Experimental Reactor (ITER) Nb3Sn production accounting for the three-dimensional (3D) nature of strain is significant for the analysis of the performance of magnet systems. A simple model for the 3D strain dependence of the critical current density in ITER Nb3Sn strands is proposed in this paper. It is on the basis of the strain-induced variation in the electronic density of states at the Fermi surface. The validity of the proposed scaling law is verified by making comparisons with experimental data acquired on the bare/jacketed Nb3Sn wire. The derived 3D model in axial form is capable of adequately describing the anomalies in the strain function of the Nb3Sn wires jacketed with AISI 316 L stainless steel, which arise from a multi-dimensional strain effect, while none of the existing research models can describe such trend. The model provides a new way of identifying the scaling relation for the critical current density in Nb3Sn strands.

TL;DR: In this article, a phenomenological model based on the idea that the ideal resistivity must approach some limiting value in the regime where the mean free path becomes comparable to the interatomic spacing is presented.

Abstract: A discussion of some of the difficulties with previous analyses of the resistivity of $A\ensuremath{-}15$ compounds is given. Precise high-temperature data on $\ensuremath{\alpha}$-particle- and electron-damaged ${\mathrm{Nb}}_{3}$Ge and ${\mathrm{Nb}}_{3}$Sn samples with different defect concentrations are presented here and analyzed in a simple way with use of a phenomenological model based on the idea that the ideal resistivity must approach some limiting value in the regime where the mean free path becomes comparable to the interatomic spacing.

TL;DR: The high temperature, normal state resistivity of strong coupled superconducting transition metal compounds and other materials with high resistivities saturates at a value corresponding to an electron mean free path of order the interatomic spacing as mentioned in this paper.

Abstract: The high temperature, normal state resistivity of strong coupled superconducting transition metal compounds and other materials with high resistivities saturates at a value corresponding to an electron mean free path of order the interatomic spacing. This accounts for the nonlinear temperature dependence of the resistivity observed in these compounds at high temperature.

TL;DR: The theory of electrical resistance developed by Bloch and others reats the conduction electrons as moving independently of one another but interacting with the lattice vibrations as discussed by the authors, and gives for the resistance of a metal, subject to certain simplifying assumptions, the formula R = const.

Abstract: The theory of electrical resistance developed by Bloch and others reats the conduction electrons as moving independently of one another but interacting with the lattice vibrations. The theory gives for the resistance of a metal, subject to certain simplifying assumptions, the formula R = const. G (ʘ/T) G ( x ) = 5/x5 ∫x o ξ4dξ/eξ-1 - 1/ex-1, (1) where ʘ is the Debye characteristic temperature. At low temperatures formula (1) leads to the conclusion that R varies as T5. The function G ( x ) was first proposed by Gruneisen.

Abstract: 1·1. The conductivity of a pure metal depends upon a large number of quantities, and it is difficult to decide the relative importance of the various constants since they often produce compensating effects. It is, however, generally agreed that the low conductivity of the divalent metals, and especially of bismuth, is due to the small effective number of conduction electrons. It has further been suggested by Mott (1935, 1936a, 1936b) that the low conductivity of the transition elements, which are even worse conductors than the divalent elements, is due to another cause, namely, to the abnormal smallness of the free path. The transition metals possess conduction electrons in an s-band and they also have unfilled d-bands. Hence, in addition to the normal s-s transitions the electrons can also undergo s-d transitions, and this results in a shortening of the free path. One of the difficulties in the way of a complete theory is the necessity of separating the normal s-s transitions from the s-d transitions, and so far it has not proved possible to do this. In the present paper it is shown that the resistances produced by the two different types of transition have different temperature variations, and therefore that it should be possible to estimate their relative importance by measurements over a sufficiently large range of temperature.

TL;DR: In this article, defects or phonons are included in Boltzmann transport theory and an interband conduction channel opens up which might account for the parallel-resistor effect seen in "saturation" of dc resistance of metals.

Abstract: Disorder such as defects or phonons causes interband scattering and renormalization effects. When these are included in a generalization of Boltzmann transport theory, an interband conduction channel opens up which might account for the "parallel-resistor" effect seen in "saturation" of dc resistance of metals.