Compounds having beta tungsten structure exist as solid solutions over composition range of several percent. However, for most of these compounds, relationship between composition and superconducting transition temperature is not known

Bozowski, S.

Gittleman, J. T.

Hanak, J. J.

Pellicane, J. P.

English

NASA Technical Reports Server

October 1971	 Brief 71-10385 
NASA TECH BRIEF 
Marshall Space Flight Center 
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/ 
Superconductor Transition Temperatures Study 
.
Intermetallic superconducting compounds crystal-
lizing in the beta-tungsten structure have been in-
vestigated in an effort to optimize their super-
conductive properties. Detailed phase-diagram data 
have revealed that compounds having the beta-tung-
sten structure exist as solid solutions over a com a-
position range of several percent. However, for 
most of these compounds, the relationship between 
composition and the superconducting transition 
temperature (T) is not known. 
In this investigation, several binary alloy systems 
(V-Si, Nb-Al, Nb-Au, Nb-Ge, Nb-Sn, Nb-Pt, and 
Ta-Ge) of the beta tungsten structure were syn-
thesized over a range of compositions by an rf-
sputtering technique, and Tc was measured at close 
composition intervals. The rf-sputtering arrangement 
included two half-disks, each composed of the 
desired constituent element and placed side by side 
on a metal electrode connected to an rf power sup-
ply. The substrates, made of dense alumina plates, 
were cooled to 77 K and positioned horizontally 
above the disks at right angles to their interface 
so as to obtain maximum composition range. 
Through a 2 mm wide mask along the entire sub-
strate length, films ranging from 0.3 p m to 1.0 pm 
(3,000 to 10,000 A) were sputtered at a pressure of 
0.66 N/rn 2 (5 x 10 3 torr) in argon. The films were 
then annealed in quartz tubes dynamically evacuated 
to 1.33 pN/m 2 (lx 10 8 torr) by an ion pump. After 
the annealing, 50 regularly spaced gold contacts 
were evaporated across the sample film. DC re-
sistance and TC measurements were then made for the 
entire specimen at compositional intervals of ap-
proximately 1.5%.
The chemical analysis was based on X-ray 
fluorescence measurements. Its absolute accuracy 
was estimated to be approximately 5 atomic percent, 
whereas the accuracy of the compositional variation 
for adjacent samples was estimated to be a few 
tenths of a percent. Structural analysis by X-ray 
diffraction techniques was possible for only the 
thickest films (1.0 pm). 
The compositional ranges of the binary sputtered 
films were as much as 70 atomic percent, and each 
case included the composition range at which the 
beta-tungsten structure would be expected to exist. 
The Tc
 and resistivity data were plotted as a function 
of composition for each system except Nb-Au. The 
smooth variation observed in the resistivity ratio 
(ratio of resistivities at room temperature and at a 
temperature just above T) reflects the uniform 
background conditions in a given run, as well as a 
smooth and continuous compositional variation. 
In several instances, pronounced maxima in the 
resistivity ratio, accompanied by narrow transition 
widths, are indicative of compound formation and 
possibly of an approach to a single phase. Transi-
tion temperatures were the same as, or within about 
I degree Kelvin of, the highest Tc reported for 
bulk materials, even though the sputtered films 
ranged in thickness. 
The sputtering technique proved capable of 
yielding metastable as well as stable compositions. 
Preparing the entire range of compositions in one 
run has the advantage of eliminating specimen 
property changes as a result of random environ-
mental changes.
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19710000383 2020-03-17T02:28:52+00:00Z
Notes: 
1. The results of this investigation establish the 
validity of the rf-sputtering approach and justify 
continuing the Tc optimization efforts; i.e., tem-
perature-time annealing studies, followed by 
detailed structural determinations. 
2. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95)
Reference: 
NASA-CR-110432 (N71-30793), Study of 
Transition Temperatures in Superconductors. 
Patent status: 
No patent action is contemplated by NASA. 
Source: J. J. Hanak, J. I. Gittleman,

S. Bozowski, and J. P. Pellicane of

RCA Corp.
under contract to

Marshall Space Flight Center

(MFS-21247)
C 
C 
Brief 7 1- 10385	 Category 03


Superconductor transition temperatures study

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