Specific Heat and Superconductivity of Binary Alloys Containing V, Nb, and Ta

Abstract

The electronic specific heat coefficient, y, the Debye temperature, OD, and the superconducting transition temperature, T,, have been measured for binary b.c.c. alloys of V, Nb, and Ta. These results have been used to investigate the effects of compositional changes on parameters used in the theory of superconductivity to describe the transition temperature. It has been shown that changes in transition temperature with changes in composition cannot be explained simply on the basis of an alteration of the density of states except in the case of binary Nb-Ta alloys. It is concluded that, for V-Nb and V-Ta alloys, changes in the interaction responsible for superconductivity also govern changes in the transition temperature.La coefficient du chaleur specifique Blectronique, y, la t e m p h t u r e de Debye, OD, et la temperature de transition supraconductrice, T,, ont BtB dBterminBs pour des alliages binaires dc type cubique centre et qui contiennent V, Nb et Ta. L'on a utilise ces resultats afin d'Btudier l'influence de composition sur des paramhtres ceux qui expliquent la tempbrature de transition dans la t,heorie de supraconductivith. L'on ne peut pas expliquer la variation dans la tempbrature de transition en fonction de la composition par le changement de la densitk; d'htats, sauf pour lea alliages Nb-Ta. L'on concluit que pour des alliages V-Nb et V-Ta, des variations dans l'interaction responsible pour la supraconductivit6 dbterminent des variations dans la t e m p h t u r e de transition.

Spin Fluctuation Depressed Superconductivity in Nb‐V Alloys

“…For the Nb rich region and for concentrations up to about 50 atyo V there is rather good quantitative agreement of about 5% between observed T, and the calculation with y and 8 from Corsan and Cook [28]. The yand &values of Ishikawa and Toth [29] underestimate T, considerably in the dilute region possibly indicating that the minimum in y and 0 observed by them is not a real effect.…”

“…Therefore the calculation has been repeated for both sets of values. The results are illustrated in Table 1 for the specific heat data of [28]. The constant k in (6) has been adjusted for pure Nb to agree with the experimental dp/dT and the value of 1 calculated from (3) using the experimental T, and 8 and the assumption of p* = 0.13 and A,, = 0. p* is not an adjustable parameter but values for Nb and V are chosen that seem reasonable from earlier work.…”

“…I n this section we discuss a few topics that from different points of view support the concept of spin fluctuations in Nb-V. -TaV 0.07 [28]…”

Superconductivity in ZrxNb1−2xMox alloys: Possible dominance of a soft phonon mode

“…Equations (3) and (7) Table I (e)2) = co~2(e))F(e)) de) ot2(e))F(e))e)-1 de) (11) to test the assumed linear interpolation of ~/. [F(e)) is the phonon density of states, e)e is the spectrum cutoff frequency, at2(e)) is an averaged electronphonon interaction parameter.…”

“…In the absence of such information (e)2> is sometimes estimated by setting ot2(e))= const to define (e)2) N from Eq. (11), which can be determined from a knowledge of F(e)) alone. The latter can be obtained from thermal neutron inelastic scattering experiments (or possibly heat capacity experiments*).…”