Impurity stabilized A15 Nb/sub 3/Nb: a new superconductor
We have succeeded in preparing by chemical vapor deposition essentially single-phase, A15 Nb/sub 3/Nb with the addition of small amounts of Ge or Si. The compositions and lattice parameters of the five samples reported on here are as follows: Nb/sub 3/(Nb/sub 0.92/Ge/sub 0.08/), 5.239 A; Nb/sub 3/(Nb/sub 0.82/Ge/sub 0.18/), 5.230 A; Nb/sub 3/(Nb/sub 0.71/Ge/sub 0.29/), 5.219 A; Nb/sub 3/(Nb/sub 0.61/Si/sub 0.39/), 5.213 A; Nb/sub 3/(Nb/sub 0.46/Si/sub 0.54/), 5.192 A. Using these compositions and lattice parameters, the lattice parameter for pure A15 Nb/sub 3/Nb is found to be 5.250 +- 0.005 A. The low-temperature specific heat of all five samples was measured from 1.4 to 11 K, showing bulk superconducting transitions in all cases, with T/sub c/ midpoint and ..delta..C/..gamma..T/sub c/ values as follows: Nb/sub 3/(Nb/sub 0.92/Ge/sub 0.08/), 5.2 K and 1.24; Nb/sub 3/(Nb/sub 0.82/Ge/sub 0.18/), 4.15 K and 1.16; Nb/sub 3/(Nb/sub 0.71/Ge/sub 0.29/), 3.6 K and 1.27; Nb/sub 3/(Nb/sub 0.61/Si/sub 0.39/), 5.4 K and 0.78; Nb/sub 3/(Nb/sub 0.46/Si/sub 0.54/), 3.4 K and 1.16. Transition widths were in general quite narrow, less than 0.5 K, and for Nb/sub 3/(Nb/sub 0.71/Ge/sub 0.29/), the transition width was 0.15 K. From the specific-heat measurements A15 Nb/sub 3/Nb has a T/sub c/ of approx. 6 K, a THETA/sub D/ of 270 +- 10 K, equivalent to that of bcc elemental Nb, and a density of states of 1.22 +- 0.1 states/eV atom. Microprobe analysis of the A15 Nb/sub 3/Nb samples shows no detectable oxygen, i.e., <0.2 at. %. In addition to the essentially single-phase samples, a predominantly A15 sample with a/sub 0/=5.246 A and 50% bcc Nb second phase has been prepared, with less than 3% of the B-site atoms occupied by Ge, showing that A15 Nb may be stabilized by less than 1% second-atom additions.
- Research Organization:
- University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico 87545
- OSTI ID:
- 5381116
- Journal Information:
- Phys. Rev., B: Condens. Matter; (United States), Journal Name: Phys. Rev., B: Condens. Matter; (United States) Vol. 21:11; ISSN PRBMD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360101 -- Metals & Alloys-- Preparation & Fabrication
360102 -- Metals & Alloys-- Structure & Phase Studies
360104* -- Metals & Alloys-- Physical Properties
ALLOY SYSTEMS
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DEBYE TEMPERATURE
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ENERGY-LEVEL DENSITY
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NIOBIUM SILICIDES
PHYSICAL PROPERTIES
SILICIDES
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SPECIFIC HEAT
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