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Study of the superconducting transition of InTl alloys in the martensitic two phase region
Volume 62A, number 2
25 July 1977
PHYSICS LETTERS
STUDY OF THE SUPERCONDUCTING TRANSITION OF l n - T l ALLOYS IN THE MARTENSITIC TWO PHASE REGION R.M. CATCHINGS and David Y. CHUNG Physics Department, Howard University, Washington, D.C. 20059, USA Received 24 May 1977 The a.c. magnetic susceptibility measurements of T c for some I n - T 1 alloys are presented. The samples are of such composition that the f.c.t, and f.c.c, phases of the martensitic transition should co-exist near T c. A double transition, characteristic of a two phase system, is observed and the T c of the individual phases determined.
The purpose of this paper is to report the results of a.c. magnetic susceptibility studies of the superconducting transition temperature of some In-T1 alloys. The samples studied are in the concentration region where the low temperature f.c,t, to f.c.c, martensitic transformation should be occurring. Recently, there has been much interest in the relationship between the superconducting transition and lattice softening. The In-T1 alloy system is of interest in this regard for it has been shown [1] that an acoustic soft mode is closely associated with its martensitic transformation. Much work has been done on In-T1 alloys [2, 3], some of which has suggested the co-existence of the f.c.c, and Lc.t. phases, however there has been no direct observation of the presence of the two phases. The In-T1 samples were prepared by a horizontal zone technique. They have been carefully examined by X-ray diffraction at room temperature and the Laue pattern showed that they were high quality single crystals. Some of the samples have been subjected to spectroscopic analysis to confirm the compositions. An independent study of the same samples have been made with ultrasonics [4], and the results of martensitic transformation temperatures are consistent with the phase diagram of [3]. The a.c. magnetic susceptibility studies were made using a mutual induction technique, that allowed both components of the complex susceptibility to be measured simultaneously. All measurements were preformed at a frequency of 450 Hz. Measurements were performed on In-T1 samples of compositions 30, 30.25, and 31 at. % TI. These samples are within the composition region where the phase diagram of the low temperature martensitic transformation, determined by Pollock and King [3], indicated
. . . . .
'
'.2.- . . . . .
.'_ .'.._L
'
'
/
/
1,0
X
" " **"
x~ 2,0
70
•
•
AT, */. TL •
30,28 AT, % TL 31 AT. 0/* TL
X
I
/ 3,0
,6
%"
,4
_:._....~ ,
,
• ,
j ,~x. .
~5:
....
vwvvw v~tL 3.3
3.4
TEMPERATUflE ( * K )
Fig. 1. Magnetic susceptibility measurements of the superconducting transition for In-T1 alloys of compositions 30, 30.25, and 31 at.%Tl. The upper curves are the change in the real part of the susceptibility X', and the lower curves are the change in the imaginary part of the susceptibility x".
the co-existence of tetragonal and cubic microstructure The results of the susceptibility measurements are given in fig. 1. The measurements show two superconducting transitions occur in some of the samples. The imaginary part of the susceptibility exhibits peaks in115
Volume 62A, number 2
PHYSICS LETTERS
Table 1 List of experimental results of superconducting transition temperatures in two phase region of In-T1 alloys. Sample (In with at. % T1)
Tc f.c.t. (K)
Tc f.c.c. (K)
"~Tc (K)
30 30.25 31
3.175 3.21 3.195
3.34-3.28 3.315
0.11 0.14 0.20
dicating the transitions in great detail. The double transitions observed, we propose are due to the f,c.c, and the f.c.t, phases. Similar results have been observed in other multiphase systems [5]. Thus the results for the 30% TI sample which gives the lowest transition temperature, we assume is due to the f.c.t, phase. This assumption would not imply that the f.c.c, phase is not present in this sample, for the microstructure o f the sample could be such as to shield out the effect of the cubic phase. The results for the samples o f 30.25 and 31 at. % T1 shows two superconducting transitions which we propose are due to the higher T c f.c.c, phase and the lower T c f.c.t, phase. Using this interpretation, we can assign a transition temperature to each phase. These values are given i l table 1, where the peak of the ×" component was used to indicate the T c. The width A T e of the complete transition is also included in table 1. We believe that our results are the first measurements for this system that directly show the presence of both phases. Previous studies on the In-T1 alloy system [2, 6], 1/ave found the general result of the enhancement of the superconducting transition temperature for the whole In-T1 system in the two phase region. Our work indicates that the enhanced T e value reported in these other studies [2, 6] must be that o f the f.c.c, phase. Our results allow the change in the transition temperature with composition o f each individual phase to be determined. The maxima observed in the imaginary component of the susceptibility has been observed in many other superconducting materials and has been related to the formation o f a filamentary, superconducting structure
116
25 July 1977
near the transition temperature [7]. The martensitic transformation in the In-T1 alloy system has been found to occur with the formation of aprallel-sided bands, associated with strains across the interface of the phases [3]. We believe that the peaks observed in our results are directly related to these bands due to the martensitic transition. Further work is in progress to grow more samples that would allow the low temperature martensitic transition to be studied in great detail. A recent paper by McMillian has suggested the non-existence of the tetragonal phase in A15 compounds below T c [8]. It is of interest whether or not McMillian's conclusion for the A15 system hold for the In-T1 system. A very detailed study of the compounds near the two-phase region could possibly determine this. We would like to acknowledge the partial support of this work by the National Science Foundation.
References [1] N.G. Pace and G.A. Saunders, Proc. Roy. Soc. Lond. A326 (1972) 521; D.J. Gunton and G.A. Saunders, Solid State Commun. 12 (1973) 569, 14 (1974) 865; D.Y. Chung, D.J. Gunton and G.A. Saunders, Phys. Rev. B13 (1976) 3239. [2] L. Guttman, J. Metals, 188 (1950) 1472; J.W. Stout and L. Guttman, Phys. Rev. 88 (1952) 703; H.L. Luo, J. Hagan and M.F. Merriam, Acta Met. 13 (1965) 1012. [3] J.T.A. Pollock and H.W. King, J. of Mat. Sci. 3 (1968) 372. [4] D.Y. Chung and G.A. Saunders, to be published. [5] M.F. Merriam, M.A. Jensen and B.R. Coles;Phys. Rev. 130 (1963) 1719. [6] M.F. Merriam, J. Hagen and H.L. Luo, Phys. Rev. 154 (1967); R.C. Dynes, Phys. Rev. B2 (1970) 644. [7] E. Maxwell and M. Strongin, Phys. Rev. Lett. 10 (1963) 212; M. Strongin, E. Maxwelland T.B. Reed, Rev. Mod. Phys. 36 (1964) 164. [8] G. Bflbro and W.L. MeMillian, Phys. Rev. B14 (1976) 1887.
25 July 1977
PHYSICS LETTERS
STUDY OF THE SUPERCONDUCTING TRANSITION OF l n - T l ALLOYS IN THE MARTENSITIC TWO PHASE REGION R.M. CATCHINGS and David Y. CHUNG Physics Department, Howard University, Washington, D.C. 20059, USA Received 24 May 1977 The a.c. magnetic susceptibility measurements of T c for some I n - T 1 alloys are presented. The samples are of such composition that the f.c.t, and f.c.c, phases of the martensitic transition should co-exist near T c. A double transition, characteristic of a two phase system, is observed and the T c of the individual phases determined.
The purpose of this paper is to report the results of a.c. magnetic susceptibility studies of the superconducting transition temperature of some In-T1 alloys. The samples studied are in the concentration region where the low temperature f.c,t, to f.c.c, martensitic transformation should be occurring. Recently, there has been much interest in the relationship between the superconducting transition and lattice softening. The In-T1 alloy system is of interest in this regard for it has been shown [1] that an acoustic soft mode is closely associated with its martensitic transformation. Much work has been done on In-T1 alloys [2, 3], some of which has suggested the co-existence of the f.c.c, and Lc.t. phases, however there has been no direct observation of the presence of the two phases. The In-T1 samples were prepared by a horizontal zone technique. They have been carefully examined by X-ray diffraction at room temperature and the Laue pattern showed that they were high quality single crystals. Some of the samples have been subjected to spectroscopic analysis to confirm the compositions. An independent study of the same samples have been made with ultrasonics [4], and the results of martensitic transformation temperatures are consistent with the phase diagram of [3]. The a.c. magnetic susceptibility studies were made using a mutual induction technique, that allowed both components of the complex susceptibility to be measured simultaneously. All measurements were preformed at a frequency of 450 Hz. Measurements were performed on In-T1 samples of compositions 30, 30.25, and 31 at. % TI. These samples are within the composition region where the phase diagram of the low temperature martensitic transformation, determined by Pollock and King [3], indicated
. . . . .
'
'.2.- . . . . .
.'_ .'.._L
'
'
/
/
1,0
X
" " **"
x~ 2,0
70
•
•
AT, */. TL •
30,28 AT, % TL 31 AT. 0/* TL
X
I
/ 3,0
,6
%"
,4
_:._....~ ,
,
• ,
j ,~x. .
~5:
....
vwvvw v~tL 3.3
3.4
TEMPERATUflE ( * K )
Fig. 1. Magnetic susceptibility measurements of the superconducting transition for In-T1 alloys of compositions 30, 30.25, and 31 at.%Tl. The upper curves are the change in the real part of the susceptibility X', and the lower curves are the change in the imaginary part of the susceptibility x".
the co-existence of tetragonal and cubic microstructure The results of the susceptibility measurements are given in fig. 1. The measurements show two superconducting transitions occur in some of the samples. The imaginary part of the susceptibility exhibits peaks in115
Volume 62A, number 2
PHYSICS LETTERS
Table 1 List of experimental results of superconducting transition temperatures in two phase region of In-T1 alloys. Sample (In with at. % T1)
Tc f.c.t. (K)
Tc f.c.c. (K)
"~Tc (K)
30 30.25 31
3.175 3.21 3.195
3.34-3.28 3.315
0.11 0.14 0.20
dicating the transitions in great detail. The double transitions observed, we propose are due to the f,c.c, and the f.c.t, phases. Similar results have been observed in other multiphase systems [5]. Thus the results for the 30% TI sample which gives the lowest transition temperature, we assume is due to the f.c.t, phase. This assumption would not imply that the f.c.c, phase is not present in this sample, for the microstructure o f the sample could be such as to shield out the effect of the cubic phase. The results for the samples o f 30.25 and 31 at. % T1 shows two superconducting transitions which we propose are due to the higher T c f.c.c, phase and the lower T c f.c.t, phase. Using this interpretation, we can assign a transition temperature to each phase. These values are given i l table 1, where the peak of the ×" component was used to indicate the T c. The width A T e of the complete transition is also included in table 1. We believe that our results are the first measurements for this system that directly show the presence of both phases. Previous studies on the In-T1 alloy system [2, 6], 1/ave found the general result of the enhancement of the superconducting transition temperature for the whole In-T1 system in the two phase region. Our work indicates that the enhanced T e value reported in these other studies [2, 6] must be that o f the f.c.c, phase. Our results allow the change in the transition temperature with composition o f each individual phase to be determined. The maxima observed in the imaginary component of the susceptibility has been observed in many other superconducting materials and has been related to the formation o f a filamentary, superconducting structure
116
25 July 1977
near the transition temperature [7]. The martensitic transformation in the In-T1 alloy system has been found to occur with the formation of aprallel-sided bands, associated with strains across the interface of the phases [3]. We believe that the peaks observed in our results are directly related to these bands due to the martensitic transition. Further work is in progress to grow more samples that would allow the low temperature martensitic transition to be studied in great detail. A recent paper by McMillian has suggested the non-existence of the tetragonal phase in A15 compounds below T c [8]. It is of interest whether or not McMillian's conclusion for the A15 system hold for the In-T1 system. A very detailed study of the compounds near the two-phase region could possibly determine this. We would like to acknowledge the partial support of this work by the National Science Foundation.
References [1] N.G. Pace and G.A. Saunders, Proc. Roy. Soc. Lond. A326 (1972) 521; D.J. Gunton and G.A. Saunders, Solid State Commun. 12 (1973) 569, 14 (1974) 865; D.Y. Chung, D.J. Gunton and G.A. Saunders, Phys. Rev. B13 (1976) 3239. [2] L. Guttman, J. Metals, 188 (1950) 1472; J.W. Stout and L. Guttman, Phys. Rev. 88 (1952) 703; H.L. Luo, J. Hagan and M.F. Merriam, Acta Met. 13 (1965) 1012. [3] J.T.A. Pollock and H.W. King, J. of Mat. Sci. 3 (1968) 372. [4] D.Y. Chung and G.A. Saunders, to be published. [5] M.F. Merriam, M.A. Jensen and B.R. Coles;Phys. Rev. 130 (1963) 1719. [6] M.F. Merriam, J. Hagen and H.L. Luo, Phys. Rev. 154 (1967); R.C. Dynes, Phys. Rev. B2 (1970) 644. [7] E. Maxwell and M. Strongin, Phys. Rev. Lett. 10 (1963) 212; M. Strongin, E. Maxwelland T.B. Reed, Rev. Mod. Phys. 36 (1964) 164. [8] G. Bflbro and W.L. MeMillian, Phys. Rev. B14 (1976) 1887.