- Email: [email protected]
Comments on superconducting phases in the Mo-Tc system
LETTERS
TO THE
We plan to extend these studies to other elements, including nickel and silver.
E. L. LEE
Lawrence Radiation Laboratory, University of California, Livermore, Cahyornia
R. G. GUTMACHER
References 1. SCHNEPPO., J. Phys. Chem. Solids 17, 188 (1961). 2. MOORE C. E., -4 Multiplet Table of Astrophysical Interest, Revised Ed. Princeton University Observatory, Princeton, New Jersey (1945).
Comments
on superconducting MO-Tc system*
phases in the
(Recemed 11 July 1962; revised 14 September IN
RECENT papers
COMPTON
1962)
and * Except as noted in the acknowledgement, this work was performed at the Argonne National Laboratory under the auspices of the U.S. Atomic Energy Commission.
et
al.,(l)
1825
EDITOR
MATTHIAS@ have discussed the superconducting transition temperatures of alloys in the MO-Tc system. Alloys of 60 and 75 at. per cent Tc, which showed transitions at 15°K and 16°K respectively, were assumed to be terminal solid solution alloys.(s) A survey(s) of the intermediate phases formed when Tc is alloyed with transition elements has included a crystallographic study of the phases in MO-Tc alloys. Results of this study indicate the occurrence of intermediate phases at 60 and 75 at. per cent Tc rather than the terminal solid solutions assumed in the previous paper.(s) Pertinent information obtained in the present investigation regarding phase relations in the MO-Tc system is presented in Table 1. The alloys were prepared by arc melting on a water-cooled copper hearth in an inert gas atmosphere. They were annealed in evacuated quartz capsules and water. quenched. The phases present in the alloys were identified by X-ray diffraction of powders prepared from bulk specimens.
Table 1. Alloys prepared and crystal structures identi$ed in the MO-Tc Intended composition (at. per cent)
system
as-cast
Phases observed? annealed
25 Tc
~-MO U-MO
cr-MO LX-MO
2 days at 7OO”C$ 1 week at 1050°C
33.3 Tc
U-MO U-MO
U-MO ~-MO
2 days at 7OO”C$ 3 weeks at 1050°C
50 Tc
U-MO U-MO -
Thermal
history
CraO-type+ ~-MO CrsO-type + cr-MO
3 weeks at 1050°C 3 weeks at 600°C
CraO-type + ~-MO
3 weeks at 1050°C
56 Tc
U-MO ~-MO
CrsO-type + sigma CrsO-type + sigma
3 weeks at 1050°C 3 weeks at 600°C
60 Tc
CrsO-type
CraO-type + sigma
2 days at 7OO”C$
70 Tc
sigma
75 Tc 77 Tc
53 Tc
85.7 Tc
sigma
2 weeks at 1050°C
sigma + fl-Tc
sigma
2 days at 7OO”C$
sigma + /3-Tc
sigma + fi-Tc
5 weeks at 500°C
fl-Tc + sigma
2 days at 7OO’C
b-Tc
t The major phase is given first in the case of two-phase alloys. $ Previously homogenized for two days at 1050°C.
LETTERS
1826
TO
The crystallographic data obtained for alloys in the as-cast condition indicate the occurrence of a sigma phase in the vicinity of 75 at. per cent Tc and a CraO-type phase at 60 at. per cent Tc. The diffraction results on annealed alloys confirm the occurrence of a sigma phase in the range of 70-75 at. per cent Tc but indicate that the Tc concentration in the Cr&-type phase is in fact 54 + 2 at. per cent. This composition for a CrsO-type phase is unique in that it represents a large deviation from the usual AaB stoichiometry. It may be that Tc is occupying some of the sites in the structure that would normally be taken up by MO atoms. Unfortunately, the atomic scattering factors of MO and Tc are too close to discern, with the usual X-ray radiation available, whether there is a preference for the available lattice sites. Table 2 gives the lattice d-spacings and intensities obtained for the C&type phase in a 56 at. per cent Tc alloy which had been annealed 3 weeks at 1050°C and water quenched. The X-ray pattern was obtained using filtered Cu radiation with a Straumanis-type Debye-Scherrer camera, An a0 = 4.9408 of:0~0002 A was determined from high angle lines by Cohen’s least-squares method. In computing intensities the phase was assumed to have the composition (Riloo.ssTco.~&sTc. The structure belongs to the space group Oi-Pm3n. The calculated intensities are the product of the Lorentz-polarization factor, the multiplicity factor and F2, the structure factor. There is good agreement between the calculated and observed dspacings and intensities. An X-ray diffraction pattern of the sigma phase in an alloy containing 70 at. per cent Tc, which had been annealed 2 weeks at 1050°C and water quenched, gave the following lattice constants : co = 4.9448i_:O*OO13 A, a0 = 9*5091+0~0004 A, and c/a = 0.520. A measurement of the superconducting transition temperature, T,, was made on an as-cast alloy containing 60 at. per cent Tc and possessing a single phase CrsO-type structure. The transition from the superconducting to the normal state was found to occur within a temperature interval of 0*3”K and was complete at 13+4”K. This differs slightly with the T, = 15°K reported by COMPTON et aA
for an as-cast
Despite
the
alloy of similar
occurrence
of
the
compo$tion. brittle
phases,
THE
EDITOR
Table 2. X-day diffraction intensities and.d-spacings for the CraO-type corn~~d ha&g the corn~o~tio~ ‘G54~~04t3 _.._
Indices
d-spacings (A)
0 23 65 100 0 0 5 13 23 30
-
-
0
-
I.105 1.078 1,053 1.009
1.104 1.075 1 *OS2 -
10 25 9 0.5
0.9690
-
0.5
3,494 2.470 2.210 2.017 I.747 1562 1.426 I.370 1.320 1.235
110 200 210 211 220 310 222 320 321 400 411 330 1 420 421(a1) 332(al) 422 510 431 1
Intensity
1.165
2.466 2 *207 2.016 1.425 1.369 l-319 1.234
MS S 8 W M MS M
MW MS MW -
~~!$l)
0.91748
0.91738
27
MS
521(orl) 440(x1) 44O(@z) 530 433 I
0.90206 0‘87342
0.90217 O-87328 O-87332
15 36
M M
0
-
;$.I)
0.82347
0.84734
0.82347
11
M
M
0.82351
3@2,
610(%) 610(~)
0.81226
0.81222 0.81220
9
$)(=1)
0~80150
0.80149
43
S
0.80151
* Letter
designations
S = Strong MW
have the following
meanings:
MS = Medium Strong M = Medium = Medium Weak W = Weak
MO-Tc alloys remain interesting as possible material for superconducting magnets.(l) As is indicated in Table 1, alloys in the composition range where the C&O-type phase appears in annealed alloys will contain the relatively ductile rx-MO solid solution in the as-cast condition, permitting the use of conventional fabrication techniques.
LETTERS
TO
Acknowledgement-The authors are indebted to Dr. A. L. GIORGI of the Los Alamos Scientific Laboratory for the use of equipment and assistance with the transition temperature measurement and to Mr L. J. NORTON and Mr. J. W. DOWNEY for assistance in the experimental work.
Argonne National Laboratory, Argonne, Illinois
J. B. DARBY,Jr. S. T. ZEGLER
THE
1827
EDITOR References
1. COMPTON V. B., CORENZWIT E., MAITA J. P.. MATTHIAS B. T. and MORIN F. J., Phys. Rev. 123, 1567 (1961). 2. MATTHIAS B. T., Rev. Mod. Phys. 33,499 (1961). 3. DARBY J. B,, Jr., LAM D. J., NORTON L. J. and DO~NEY J. W., J. of Less-Common Metals, in Press.
TO THE
We plan to extend these studies to other elements, including nickel and silver.
E. L. LEE
Lawrence Radiation Laboratory, University of California, Livermore, Cahyornia
R. G. GUTMACHER
References 1. SCHNEPPO., J. Phys. Chem. Solids 17, 188 (1961). 2. MOORE C. E., -4 Multiplet Table of Astrophysical Interest, Revised Ed. Princeton University Observatory, Princeton, New Jersey (1945).
Comments
on superconducting MO-Tc system*
phases in the
(Recemed 11 July 1962; revised 14 September IN
RECENT papers
COMPTON
1962)
and * Except as noted in the acknowledgement, this work was performed at the Argonne National Laboratory under the auspices of the U.S. Atomic Energy Commission.
et
al.,(l)
1825
EDITOR
MATTHIAS@ have discussed the superconducting transition temperatures of alloys in the MO-Tc system. Alloys of 60 and 75 at. per cent Tc, which showed transitions at 15°K and 16°K respectively, were assumed to be terminal solid solution alloys.(s) A survey(s) of the intermediate phases formed when Tc is alloyed with transition elements has included a crystallographic study of the phases in MO-Tc alloys. Results of this study indicate the occurrence of intermediate phases at 60 and 75 at. per cent Tc rather than the terminal solid solutions assumed in the previous paper.(s) Pertinent information obtained in the present investigation regarding phase relations in the MO-Tc system is presented in Table 1. The alloys were prepared by arc melting on a water-cooled copper hearth in an inert gas atmosphere. They were annealed in evacuated quartz capsules and water. quenched. The phases present in the alloys were identified by X-ray diffraction of powders prepared from bulk specimens.
Table 1. Alloys prepared and crystal structures identi$ed in the MO-Tc Intended composition (at. per cent)
system
as-cast
Phases observed? annealed
25 Tc
~-MO U-MO
cr-MO LX-MO
2 days at 7OO”C$ 1 week at 1050°C
33.3 Tc
U-MO U-MO
U-MO ~-MO
2 days at 7OO”C$ 3 weeks at 1050°C
50 Tc
U-MO U-MO -
Thermal
history
CraO-type+ ~-MO CrsO-type + cr-MO
3 weeks at 1050°C 3 weeks at 600°C
CraO-type + ~-MO
3 weeks at 1050°C
56 Tc
U-MO ~-MO
CrsO-type + sigma CrsO-type + sigma
3 weeks at 1050°C 3 weeks at 600°C
60 Tc
CrsO-type
CraO-type + sigma
2 days at 7OO”C$
70 Tc
sigma
75 Tc 77 Tc
53 Tc
85.7 Tc
sigma
2 weeks at 1050°C
sigma + fl-Tc
sigma
2 days at 7OO”C$
sigma + /3-Tc
sigma + fi-Tc
5 weeks at 500°C
fl-Tc + sigma
2 days at 7OO’C
b-Tc
t The major phase is given first in the case of two-phase alloys. $ Previously homogenized for two days at 1050°C.
LETTERS
1826
TO
The crystallographic data obtained for alloys in the as-cast condition indicate the occurrence of a sigma phase in the vicinity of 75 at. per cent Tc and a CraO-type phase at 60 at. per cent Tc. The diffraction results on annealed alloys confirm the occurrence of a sigma phase in the range of 70-75 at. per cent Tc but indicate that the Tc concentration in the Cr&-type phase is in fact 54 + 2 at. per cent. This composition for a CrsO-type phase is unique in that it represents a large deviation from the usual AaB stoichiometry. It may be that Tc is occupying some of the sites in the structure that would normally be taken up by MO atoms. Unfortunately, the atomic scattering factors of MO and Tc are too close to discern, with the usual X-ray radiation available, whether there is a preference for the available lattice sites. Table 2 gives the lattice d-spacings and intensities obtained for the C&type phase in a 56 at. per cent Tc alloy which had been annealed 3 weeks at 1050°C and water quenched. The X-ray pattern was obtained using filtered Cu radiation with a Straumanis-type Debye-Scherrer camera, An a0 = 4.9408 of:0~0002 A was determined from high angle lines by Cohen’s least-squares method. In computing intensities the phase was assumed to have the composition (Riloo.ssTco.~&sTc. The structure belongs to the space group Oi-Pm3n. The calculated intensities are the product of the Lorentz-polarization factor, the multiplicity factor and F2, the structure factor. There is good agreement between the calculated and observed dspacings and intensities. An X-ray diffraction pattern of the sigma phase in an alloy containing 70 at. per cent Tc, which had been annealed 2 weeks at 1050°C and water quenched, gave the following lattice constants : co = 4.9448i_:O*OO13 A, a0 = 9*5091+0~0004 A, and c/a = 0.520. A measurement of the superconducting transition temperature, T,, was made on an as-cast alloy containing 60 at. per cent Tc and possessing a single phase CrsO-type structure. The transition from the superconducting to the normal state was found to occur within a temperature interval of 0*3”K and was complete at 13+4”K. This differs slightly with the T, = 15°K reported by COMPTON et aA
for an as-cast
Despite
the
alloy of similar
occurrence
of
the
compo$tion. brittle
phases,
THE
EDITOR
Table 2. X-day diffraction intensities and.d-spacings for the CraO-type corn~~d ha&g the corn~o~tio~ ‘G54~~04t3 _.._
Indices
d-spacings (A)
0 23 65 100 0 0 5 13 23 30
-
-
0
-
I.105 1.078 1,053 1.009
1.104 1.075 1 *OS2 -
10 25 9 0.5
0.9690
-
0.5
3,494 2.470 2.210 2.017 I.747 1562 1.426 I.370 1.320 1.235
110 200 210 211 220 310 222 320 321 400 411 330 1 420 421(a1) 332(al) 422 510 431 1
Intensity
1.165
2.466 2 *207 2.016 1.425 1.369 l-319 1.234
MS S 8 W M MS M
MW MS MW -
~~!$l)
0.91748
0.91738
27
MS
521(orl) 440(x1) 44O(@z) 530 433 I
0.90206 0‘87342
0.90217 O-87328 O-87332
15 36
M M
0
-
;$.I)
0.82347
0.84734
0.82347
11
M
M
0.82351
3@2,
610(%) 610(~)
0.81226
0.81222 0.81220
9
$)(=1)
0~80150
0.80149
43
S
0.80151
* Letter
designations
S = Strong MW
have the following
meanings:
MS = Medium Strong M = Medium = Medium Weak W = Weak
MO-Tc alloys remain interesting as possible material for superconducting magnets.(l) As is indicated in Table 1, alloys in the composition range where the C&O-type phase appears in annealed alloys will contain the relatively ductile rx-MO solid solution in the as-cast condition, permitting the use of conventional fabrication techniques.
LETTERS
TO
Acknowledgement-The authors are indebted to Dr. A. L. GIORGI of the Los Alamos Scientific Laboratory for the use of equipment and assistance with the transition temperature measurement and to Mr L. J. NORTON and Mr. J. W. DOWNEY for assistance in the experimental work.
Argonne National Laboratory, Argonne, Illinois
J. B. DARBY,Jr. S. T. ZEGLER
THE
1827
EDITOR References
1. COMPTON V. B., CORENZWIT E., MAITA J. P.. MATTHIAS B. T. and MORIN F. J., Phys. Rev. 123, 1567 (1961). 2. MATTHIAS B. T., Rev. Mod. Phys. 33,499 (1961). 3. DARBY J. B,, Jr., LAM D. J., NORTON L. J. and DO~NEY J. W., J. of Less-Common Metals, in Press.