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G. Rangarajan

Bio: G. Rangarajan is an academic researcher. The author has contributed to research in topics: Calorimeter & Scattering. The author has an hindex of 1, co-authored 2 publications receiving 11 citations.

Papers
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Journal ArticleDOI
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

11 citations

Book ChapterDOI
01 Jan 1988
TL;DR: In this article, specific heat measurements were made on single phase materials of Y1-x PrxBa2Cu3O7-y (x = 0 to 0.5) from 4.2 to 60 K using a quasi-adiabatic vacum calorimeter by pulse method of heating.
Abstract: Specific heat measurements were made on single phase materials of Y1-x PrxBa2Cu3O7-y (x = 0 to 0.5) from 4.2 to 60 K using a quasi-adiabatic vacum calorimeter by pulse method of heating. The oxygen deficiency, y, was determined by iodimetry to be 0.15 + 0.05 for x = 0.1 and increased to 0.24 ± 0.05 as x reached 0.5. The Tc was measured both resistively and inductively. A plot of C/T against T2 shows a linear behaviour below 20 K. The contribution to the specific heat linear in temperature increases as the concentration x of Pr increases. Subtracting the specific heat of YBa2Cu3O7-y from that of the praseodymium doped compound, the excess specific heat due to one mole of Pr is determined for each value of x. This excess contribution decreases as x increases. The excess contribution is interpreted as due to the Schottky anomaly of Pr3+ and Pr4+ and the concentration of Pr3+ was found to decrease from 30% for x = 0.1 to 5% for x = 0.5.

Cited by
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Journal ArticleDOI
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.

63 citations

Journal ArticleDOI
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

23 citations

Journal ArticleDOI
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 .

18 citations

Journal ArticleDOI
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.

16 citations

Journal ArticleDOI
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.

12 citations