- Email: [email protected]
Low-temperature phase transformation in NbGe Al alloy
Volume 37A~ number 5
PHYSICS LETTERS
LOW-TEMPERATURE
PHASE
TRANSFORMATION
20 December 1971
IN Nb-Ge-A1
ALLOY
B. N. KODESS, Institute f o r Solid State P h y s i c s , Chernogolovka, USSR
V. B. KURITZIN and B. N. TRETJAKOV Central Research Institute f o r Ferrous Metallurgy I. P. Bardin
Received 14 October 1971
A cubic-to-tetragonal transformation is discovered in the Nb3(A1-Ge) alloy as a result of an investigation carried out at low temperatures by means of an X-ray and NMR analysis.
By m e a n s of an X - r a y and e l e c t r o n i c m i c r o p r o b e a n a l y s i s it has been r e c e n t l y shown in a n u m b e r of i n v e s t i g a t i o n s that some of the fl-W type undergo a c u b i c - t o - t e t r a g o n a l t r a n s f o r m a tion at the t e m p e r a t u r e s just above T c [1-3]. It should be noted that some a u t h o r s [4] do not cons i d e r the i m m e d i a t e v i c i n i t y of m a r t e n s i t i c and s u p e r c o n d u c t i n g t r a n s f o r m a t i o n s to be a c c i d e n tal. This vicinity, a p p a r e n t l y , is due to the g r e a t influence of the phonon s p e c t r u m on both types of t r a n s f o r m a t i o n s . Hence, the study of the r e g u l a r i t i e s of a low t e m p e r a t u r e s t r u c t u r a l t r a n s f o r m a t i o n in s u p e r c o n d u c t o r s with different T c is of s u b s t a n t i a l i n t e r e s t . C o n t r a d i c t o r y opinions have been for the c h a r a c t e r of d i s t o r tion of a unit cell. S t r u c t u r a l t r a n s f o r m a t i o n in V3Si shows m a r k e d influence on the NMR s p e c t r u m p a r a m e t e r s . G o s s a r d [5] found that when p a s s i n g into t e t r a g o n a l state the NMR s p e c t r u m of 51V in the i n t e r m e t a l l i c compound V3Si splits into t h r e e c o m p o n e n t s with different Knight shifts and q u a d r u p o l e i n t e r a c t i o n c o n s t a n t s . T h e s e changes a r e a t t r i b u t e d by the conductivity e l e c t r o n s in d - s u b b a n d s located in a n i m m e d i a t e v i c i n i t y to the F e r m i e n e r g y a c c o r d i n g to the Labbe and F r i e d e l model [6]. The p r e s e n c e of d i s t o r t i o n s in the orthogonal a t o m s chains of the t r a n s i t i v e m e t a l f o r m s the b a s i s of this model. However, u s i n g A P W - m e t h o d M a t t h e i s s [7] calculated a power s p e c t r u m for the compounds of the V3X type a s c e r t a i n i n g an i n a d e q u a t e n e s s of such a model. T a n g i b l e difficulties met with when detecting the NMR s i g n a l from the i n t r a n s i t i v e e l e m e n t made it f a r from e s t a b l i s h i n g which of the s u b l a t t i c e s underwent d i s t o r t i o n . The s u b s e q u e n t
thorough X-ray investigations on the monocrystal V3Si allowed the authors [8] to suggest that only the Si sublattice had been distorted during the martensite transition. The work [9] dealt with the Nb3Al sample. The authors believe the probability of the structural transformation in it to be rather small. The present paper is concerned with the investigation of the Nb~(AI-Ge)properties with a ratio of Al:Ge equal to 1:3. A marked increase of Tc [I0] when alloying Ge enabled us to count on the possibility of appearance of this transformation in a triple intermetallie compound. In fact. it had been found that as temperature decreased the diffraction reflex lines and NMR absorption spectrum changed. An X-ray pattern has been obtained on "Hilger" two-channeldiffractometer in a helium cryostat and the method of internal standard was used. Powder of Mo was added to the powder under investigation. The line recordings (520), (432), (521), (440) and the lines (222) of Mo at nitrogen and helium temperatures (20 + 1OK) were carried out. The distance between the line centre maximum (440) was measured on diffractograms. The change in diffraction pattern allowed to evaluate the magnitudeof the tetragonal deformation. The magnitudeof shear neglected because of thermal expansionand considering the transformation to be completely carried out then e = (3.2 + 1.2) x 10 -3. Notice that the value of 2e2 lies between the known values for V3Si and Nb3Sn , and the symbol e coincides with that of Nb3Sn. At t e m p e r a t u r e just above the t e m p e r a t u r e of the s u p e r c o n d u c t i v e t r a n s i t i o n (24 + l°K) t h e r e have been r e c o r d e d the s p e c t r a NMR 27A1 a p a r t 4J5
Volume 37A, number 5
PHYSICS L E T T E R S
20 D e c e m b e r 1971
of N M R on 27A1 n u c l e i in N b 3 ( A 1 - G e ) a r e in good a g r e e m e n t w i t h t h e h y p o t h e s i s [8] on s u b l a t t i c e d i s t o r t i o n of t h e i n t r a n s i t i v e e l e m e n t .
References
Hz 4.400
4.380
4.360
4.340
4.320
4.300
Fig. i. Absorption line NMR spectrum, a) nitrogen temperatures, b) 24°K.
from X-ray investigation. The polarising magn e t i c f i e l d i n t e n s i t y w a s 4 kOe. T h e N M R s p e c t r u m of 27A1 r e p r e s e n t i n g a s i n g l e a b s o r p t i o n line at nitrogen and higher temperatures undergoes substantial splitting at measuring tempera t u r e s (fig. 1). S u p p o s i n g t h a t in N b 3 ( A 1 - G e ) a n d V3Si s y m m e t r y of t h e low t e m p e r a t u r e p h a s e i s a n a l o g o u s t h e n t h e r e s u l t s of o u r i n v e s t i g a t i o n s
4]6
[1] B. W. B a t t e r m a n and C. S. B a r r e t , Phys. Rev. Lett e r s 13 (1964) 390. [2] J . I . K u n z l e r e t a [ . , Phys. Rev. 143 (1966) 390. [3] H.W. K i n g e t at., Phys. L e t t e r s 26A (1967) 77. [4] A. P. Levanjuk and R.A. Suris, Usp. Phys. Nauk USSR 91 (1967) 113. [5] A. C. G o s s a r d , Phys. Rev. A149 (1966) 246. [6] J. Labbe and J . J . F r i e d e l , J. Phys. 27 (1966) 153. 303. [7] L . F . M a t t h e i s s . Phys. Rev. A148 (1965) 112. [8] J. PereI, B.W. B a t t e r m a n n and E. I. Blount, Phys. Rev. 166 (1968) 616. [9] R. H. Willens, T. H. Geballe, A. C. Gossard, J . P . Malta, A. Meth, I.W. Hu[[ and R.H. Soden. Solid State Commun. 7 (1969) 837. [lO] B. N. Kodess and V. Sh. Schektman, Zh. ETF Pis. Red. 14 (1971) 338.
PHYSICS LETTERS
LOW-TEMPERATURE
PHASE
TRANSFORMATION
20 December 1971
IN Nb-Ge-A1
ALLOY
B. N. KODESS, Institute f o r Solid State P h y s i c s , Chernogolovka, USSR
V. B. KURITZIN and B. N. TRETJAKOV Central Research Institute f o r Ferrous Metallurgy I. P. Bardin
Received 14 October 1971
A cubic-to-tetragonal transformation is discovered in the Nb3(A1-Ge) alloy as a result of an investigation carried out at low temperatures by means of an X-ray and NMR analysis.
By m e a n s of an X - r a y and e l e c t r o n i c m i c r o p r o b e a n a l y s i s it has been r e c e n t l y shown in a n u m b e r of i n v e s t i g a t i o n s that some of the fl-W type undergo a c u b i c - t o - t e t r a g o n a l t r a n s f o r m a tion at the t e m p e r a t u r e s just above T c [1-3]. It should be noted that some a u t h o r s [4] do not cons i d e r the i m m e d i a t e v i c i n i t y of m a r t e n s i t i c and s u p e r c o n d u c t i n g t r a n s f o r m a t i o n s to be a c c i d e n tal. This vicinity, a p p a r e n t l y , is due to the g r e a t influence of the phonon s p e c t r u m on both types of t r a n s f o r m a t i o n s . Hence, the study of the r e g u l a r i t i e s of a low t e m p e r a t u r e s t r u c t u r a l t r a n s f o r m a t i o n in s u p e r c o n d u c t o r s with different T c is of s u b s t a n t i a l i n t e r e s t . C o n t r a d i c t o r y opinions have been for the c h a r a c t e r of d i s t o r tion of a unit cell. S t r u c t u r a l t r a n s f o r m a t i o n in V3Si shows m a r k e d influence on the NMR s p e c t r u m p a r a m e t e r s . G o s s a r d [5] found that when p a s s i n g into t e t r a g o n a l state the NMR s p e c t r u m of 51V in the i n t e r m e t a l l i c compound V3Si splits into t h r e e c o m p o n e n t s with different Knight shifts and q u a d r u p o l e i n t e r a c t i o n c o n s t a n t s . T h e s e changes a r e a t t r i b u t e d by the conductivity e l e c t r o n s in d - s u b b a n d s located in a n i m m e d i a t e v i c i n i t y to the F e r m i e n e r g y a c c o r d i n g to the Labbe and F r i e d e l model [6]. The p r e s e n c e of d i s t o r t i o n s in the orthogonal a t o m s chains of the t r a n s i t i v e m e t a l f o r m s the b a s i s of this model. However, u s i n g A P W - m e t h o d M a t t h e i s s [7] calculated a power s p e c t r u m for the compounds of the V3X type a s c e r t a i n i n g an i n a d e q u a t e n e s s of such a model. T a n g i b l e difficulties met with when detecting the NMR s i g n a l from the i n t r a n s i t i v e e l e m e n t made it f a r from e s t a b l i s h i n g which of the s u b l a t t i c e s underwent d i s t o r t i o n . The s u b s e q u e n t
thorough X-ray investigations on the monocrystal V3Si allowed the authors [8] to suggest that only the Si sublattice had been distorted during the martensite transition. The work [9] dealt with the Nb3Al sample. The authors believe the probability of the structural transformation in it to be rather small. The present paper is concerned with the investigation of the Nb~(AI-Ge)properties with a ratio of Al:Ge equal to 1:3. A marked increase of Tc [I0] when alloying Ge enabled us to count on the possibility of appearance of this transformation in a triple intermetallie compound. In fact. it had been found that as temperature decreased the diffraction reflex lines and NMR absorption spectrum changed. An X-ray pattern has been obtained on "Hilger" two-channeldiffractometer in a helium cryostat and the method of internal standard was used. Powder of Mo was added to the powder under investigation. The line recordings (520), (432), (521), (440) and the lines (222) of Mo at nitrogen and helium temperatures (20 + 1OK) were carried out. The distance between the line centre maximum (440) was measured on diffractograms. The change in diffraction pattern allowed to evaluate the magnitudeof the tetragonal deformation. The magnitudeof shear neglected because of thermal expansionand considering the transformation to be completely carried out then e = (3.2 + 1.2) x 10 -3. Notice that the value of 2e2 lies between the known values for V3Si and Nb3Sn , and the symbol e coincides with that of Nb3Sn. At t e m p e r a t u r e just above the t e m p e r a t u r e of the s u p e r c o n d u c t i v e t r a n s i t i o n (24 + l°K) t h e r e have been r e c o r d e d the s p e c t r a NMR 27A1 a p a r t 4J5
Volume 37A, number 5
PHYSICS L E T T E R S
20 D e c e m b e r 1971
of N M R on 27A1 n u c l e i in N b 3 ( A 1 - G e ) a r e in good a g r e e m e n t w i t h t h e h y p o t h e s i s [8] on s u b l a t t i c e d i s t o r t i o n of t h e i n t r a n s i t i v e e l e m e n t .
References
Hz 4.400
4.380
4.360
4.340
4.320
4.300
Fig. i. Absorption line NMR spectrum, a) nitrogen temperatures, b) 24°K.
from X-ray investigation. The polarising magn e t i c f i e l d i n t e n s i t y w a s 4 kOe. T h e N M R s p e c t r u m of 27A1 r e p r e s e n t i n g a s i n g l e a b s o r p t i o n line at nitrogen and higher temperatures undergoes substantial splitting at measuring tempera t u r e s (fig. 1). S u p p o s i n g t h a t in N b 3 ( A 1 - G e ) a n d V3Si s y m m e t r y of t h e low t e m p e r a t u r e p h a s e i s a n a l o g o u s t h e n t h e r e s u l t s of o u r i n v e s t i g a t i o n s
4]6
[1] B. W. B a t t e r m a n and C. S. B a r r e t , Phys. Rev. Lett e r s 13 (1964) 390. [2] J . I . K u n z l e r e t a [ . , Phys. Rev. 143 (1966) 390. [3] H.W. K i n g e t at., Phys. L e t t e r s 26A (1967) 77. [4] A. P. Levanjuk and R.A. Suris, Usp. Phys. Nauk USSR 91 (1967) 113. [5] A. C. G o s s a r d , Phys. Rev. A149 (1966) 246. [6] J. Labbe and J . J . F r i e d e l , J. Phys. 27 (1966) 153. 303. [7] L . F . M a t t h e i s s . Phys. Rev. A148 (1965) 112. [8] J. PereI, B.W. B a t t e r m a n n and E. I. Blount, Phys. Rev. 166 (1968) 616. [9] R. H. Willens, T. H. Geballe, A. C. Gossard, J . P . Malta, A. Meth, I.W. Hu[[ and R.H. Soden. Solid State Commun. 7 (1969) 837. [lO] B. N. Kodess and V. Sh. Schektman, Zh. ETF Pis. Red. 14 (1971) 338.