No abstract

No abstract

Matthias et al.(1) pointed out that V3Al, if it would crystallize in the p-W structure, would be a superconductor with a very high transition temperature. In this note measurements a r e reported on the superconducting transition temperatures Tc of V3A1, V3Ge and solid solutions prepared by substitution of Ga or A1 for Ge in V3Ge.of V (99.7%) with Ga (99.999%) in an induction furnace using crucibles of A1203.The ingots were annealed in argon in sealed vycor ampoules. The subsequent spectral analysis showed that Si and A1 were present in small amounts ( < 0.1%) and only in surface layers which were mechanically removed from the ingots. The phase composition was determined by the X-ray method and also metallographically. T was measured by the inductive method. The experimental e r r o r of the absolute T values was about + 0.1 deg.V-Al alloys after remelting showed the b.c.c. structure (a = 3.052 1) and were not superconducting above 2.5 OK. After annealing them for 270 h a system of extra lines appeared on the X-ray pattern, which were identified as the 8-W structure, whereas in alloys containing 24.5% A1 the p-W lines were weaker than the lines of the b. c. c. phase and rather indistinct, they were found to be prevailing and more distinct in the alloy with 24% Al. It ie of interest that the highest Tc obtained corresponds to this composition (11.15 OK for 24% Al). The value of the lattice pawmeter is somewhat lower than obtained (Fig. l) by extrapolation from data for ternary composition. Analogous dependences of T and a were observed for the system V-Ge-A1 in the papers (2 to 4). But they could not get V3Al in -W structure. Our value for the lattice conatant (4.798 0.002)% differs considerably from 4.92 $ as reported by (5), but in this reference no data about euperconduction are given. The paper (6) did not confirm its preeence under the same conditions. It ie The samples were produced by fusion of V (99.95%) with Ge. Al (99.99%) and C C C

Transverse and longitudinal magnetostrictions of a disk-shape crystalline conventional V3Si superconductor were studied by the strain gauge technique in an external magnetic field up to 12 T. It has been found that the observed magnetostriction consists of two components. The first component reveals a strong irreversibility correlated with the pinning phenomenon. The second component saturates when the external magnetic field reaches the value of the second critical field Hc2 corresponding to the changes in the free enthalpy of the superconductor in the external magnetic field. One has also observed the phenomena of the thermomagnetic avalanches, which manifest themselves as the jumps of the surface self-field of the investigated sample as well as the jumps of the magnetostriction.