ELECTRONIC AND TRANSPORT PROPERTIES OF LIQUID QUENCHED AMORPHOUS (Mo1-xxRux) 80P20 SUPERCONDUCTORS

Results of superconductive properties and magnetic susceptibilities of amorphous molybdenum based alloys obtained by liquid quenching are presented and discussed. These alloys have superconducting transition temperatures ranging from 3 K to 9 K. Correlation between Tc and magnetic susceptibility is observed. However, the predicted variation of density of states at the Fermi level with electron valence fails to explain the observed variation in the upper critical field within the framework of "dirty alloy" theories. Recently a series of amorphous molybdenum based alloys with superconducting transition temperatures up to 9 K have been obtained by liquid quenching/1/. These alloys are produced in the bulk form and are stable at and well above room temperature (spontaneous crystallization temperature at ^ 1000 K). Electron and X-ray diffraction studies of these alloys exhibit features characteristic of amorphous structure. In figure 1 is shown the Variation of transition temperature (T ) as a function of average group number (AGN) of the transition metal constituent in the alloys. The general trend of T vs AGN resembles that observed by Collver and Hammond on vapor quenched films 111. However the occurrence of the maximum T is shifted to a lower AGN c (probably < 6) as compared to their results of maximum T at AGN "J 6.5. It is conceivable that elecc tron transfer takes place from Mo to P but not from Ru to P based on the Pauling electronegativities of Mo, Ru, and P being 1.8, 2.2 and 2.1, respectively. The depletion of screening charge from Mo to P leads to a relaxation of Mo d-states. A net increase in d-band occupation could result. Such considerations may explain the apparent discrepancy in the T vs AGN curve with respect to that of reference 121. In order to understand the trend of T vs AGN, c ' magnetic susceptibility measurements are made to esResearch supported by Energy Research and Development Agency, Contract No EY-76-C-03-0822 + Present address : W.W. Hansen Laboratories of Physics, Standford University, Standford,California 94305 Hi 1 1 1 1.0 2 T ° I\ < 9 • \-— 0.8 IS A \ I ~ 7 \ \ 0 . 6 1» N u 2 N V § 5 — \ \r — o.4 " — M080 P I0 8 I0 O Q o O ( M o | . x R u x ) 8 0 P 2 0 \ « sl l l Z_J f 5 6 7 8 z (Nb) (Mo) (Tc) (Ru) Fig. 1 : Superconducting transition temperature and electronic density of states derived from magnetic susceptibility measurements vs average group number (AGN) for amorphous molybdenum alloys. timate the variation of the electronic density of states at the Fermi surface N(0) as a function of AGN. Since the experimental susceptibility x is composed of contributions from different types of electrons, certain approximations have to be made to isolate the most important contribution. The Landau term which goes inversely as the effective mass for both s and d electrons, and the core term are usually one or two orders of magnitude less than the obArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19786202 Table I : Some magne.tic a ~ d transport properties of amorphous molybdenum based alloys. 8Ru0. 2)8op20