HAL Id: jpa-00220251
https://hal.archives-ouvertes.fr/jpa-00220251
Submitted on 1 Jan 1980
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
DENSITY, COMPRESSIBILITY, SPECIFIC HEAT AND DIFFRACTION DATA OF
LITHIUM-MAGNESIUM ALLOYS
H. Ruppersberg, J. Saar, W. Speicher, P. Heitjans
To cite this version:
H. Ruppersberg, J. Saar, W. Speicher, P. Heitjans. DENSITY, COMPRESSIBILITY, SPECIFIC HEAT AND DIFFRACTION DATA OF LITHIUM-MAGNESIUM ALLOYS. Journal de Physique Colloques, 1980, 41 (C8), pp.C8-595-C8-598. �10.1051/jphyscol:19808151�. �jpa-00220251�
JOURNAL DE PHYSIQUE ColZoque C8, suppl6ment au n08, Tome 41, aoGt 1980, page C8-595
DENSITY, COMPRESSIBILITY, SPECIFIC HEAT AND DIFFRACTION DATA OF LITHIUM-MAGNESIUM ALLOYS
H. Ruppersberg, 3. Saar, W. Speicher and P. Heitjans *
F. B. Angewandte Physik der Universittit des SaarZandes, 0-6600 Saarbriicken, R. F. A.
* Fachbereich Physik der Universittit Marburg and I L L Grenoble, France.
Abstract.- For LiMg liquid alloys the density and the speed of ultrasonic waves were measured for temperatures between the liquidus and 970 +_ 80 K, depending on the sample. The specific heat at constant pressure was determined for liquid and solid alloys at the compositions xM <0.50 and
x < 0.60, respectively. The S (q) partial structure factor was measured by neutrgn diffraction in:
tfig liquid state at 695 and 875% for the zero-alloy composition 7~i0.7~g0.3. A small preference for unlike nearest neighbours is observed which diminishes with rising temperature. The volume per atom varies almost linearly with composition. However, the coefficient of thermal expansion, and the other properties which have been measured, show more or less pronounced deviation from linear behaviour. The excess specific heat is Larger for the liquid than for the solid phase.
Introduction
We study lithium alloys because the isotope 7 ~ i has a negative neutron-scattering amplitude. This al- lows the preparation of "zero-alloys" from which direct information is obtained about the distapce- correlation of concentration fluctuations as ex- plained by Chieux and Ruppersberg in these proceed- ingsl). Lithium is also a good candidate for con- ventional and non-conventignal NMR techniques as is pointed out by Heitjans et a1-2). Until now the
segregating system LiNa and the compound forming systems Li-Ag and Li-Pb have been investigated 2-6).
In the latter systems strong deviations from an ideal behaviour have been observed for the liquid phases and to a similar extent also for the solid alloys. Strong negative rxcess-volumes vXS have been observed for both phases and for LiAg it was observed that the chemical short-range order (csro) persists almost unchanged through the melting point.
The deviations from the ideal behaviour are strong-
est for the stoichiometric compositions and they are probably due to a transfer of charge from the cells containing the Li atoms to the more noble atoms.
However, a theoretical interpretation of these SYS- tems seems to be very difficult. Less problematical are Li-Mg alloys. They are sufficiently close to ideal not to discourage theoreticians, but they are far enough from ideal to be interesting. This will b e demonstrated by the following brief comneddium Of properties which have been observed for solid and liquid Li-Mg alloys. Li and Mg are both simple metals with a valence difference of one and the atoms have almost the same size. As a consequence, in the solid phase extended regions of bcc and hcp solid solutions exist which are separated by a rel- atively narrow miscibility gap ranging from about 70 to 82 at % Mg. Positron annihilation experiments of .Stewart7) and Compton profiles measured by Berndt and ~riimme~) show that LiMg is a nearly free elec- tron alloy. There are indications also from Hall
9 )
measurements of Ide , from the Kinght shift deter-
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19808151
(28-596 JOURNAL DE PHYSIQUE
mined by Lynch e t a l l o ) a n d from o p t i c a l p r o p e r t i e s measured by Mathewson and Myers1 I ) t h a t t h e Fermi s u r f a c e c o n t a c t s t h e 110 B r i l l o u i n zone boundary a t a b o u t 30 t o 40 a t % Mg. From t h e p o s i t r o n a n n i h i l - a t i o n d a t a p u b l i s h e d by Kubica e t a ~ ? ~ ) , it h a s been deduced by Tsuchiya and ~ a m a k i ' ~ ) t h a t charge i s t r a n s f e r r e d from Mg t o L i c e l l s . T h i s h a s a l s o been observed from s o f t X-ray emission s p e c t r a by C a t t e r a l l and ~ r o t t e r ' ~ ) and it h a s t h e o r e t i c a l l y been p o s t u l a t e d by 1 n g l e s f i e l d i 5 ! S i g n i f i c a n t dev- i a t i o n s from i d e a l i t y have been deduced from t h e X-ray d i f f r a c t i o n p a t t e r n s of t h e s o l i d s o l u t i o n s b y H e r b s t e i n and ~ v e r b a c h ' ~ ! For bcc s o l u t i o n s t h e l a t - t i c e parameter is s m a l l e r t h a n t h e mean v a l u e o f p u r e L i and a h y p o t h e t i c a l bcc Mg. The d e v i a t i o n i s due t o a s h o r t e n i n g of t h e LiMg d i s t a n c e s r a t h e r t h a n t o changes i n t h e atomic r a d i i and it i s s t r o n - g e s t a t a b o u t 50 a t % where $'/v amounts t o a b o u t -5%. The chemical bonding which i s r e s p o n s i b l e f o r t h i s e f f e c t r e s u l t s a l s o i n a p r e f e r e n c e f o r u n l i k e n e a r e s t neighbours which, however, is small: a t t h e equiatomic composition an atom h a s 4.3 u n l i k e near- e s t neighbours on average compared t o 4.0 i n a ran- dom and 8.0 i n an o r d e r e d s o l u t i o n . Lynch and Edwards17) observed a d e c r e a s e i n t h e c o m p r e s s i b i l i - t y of b c c a l l o y s w i t h i n c r e a s i n g Mg c o n t e n t , which i s i n accordance w i t h t h e i n c r e a s i n g m e l t i n g p o i n t o f t h e s e a l l o y s . The t h e r m a l expansion c o e f f i c i e n t s h o u l d v a r y i n a s i m i l a r way, b u t it i s l a r g e r t h a n t h e mean v a l u e o f t h e p u r e components.
E e v i a t i o n s from i d e a l i t y were a l s o observed f o r t h e p r o p e r t i e s of t h e l i q u i d phases. The a c t i v i t y co- e f f i c i e n t s (Saboungi and lander")) a r e somewhat s m a l l e r t h a n one. The i n t e g r a l e n t h a l p i e s of mixing a r e symmetrical i n composition b u t i n d i c a t e a s m a l l tendency of A-B a s s o c i a t i o n ( ~ o m m e r ' ~ ) ) . According
t o Feitsma e t al?O1, a p l o t o f t h e e l e c t r i c a l r e s i s - t i v i t y R of t h e l i q u i d a l l o y s vs. composition exhib- i t s t h e u s u a l p a r a b o l a - l i k e behaviour. However, t h e t o p i s s h i f t e d from t h e equiatomic composition toward t h e L i - s i d e . S e v e r a l t h e o r e t i c a l approaches y i e l d e d r e s i s t i v i t i e s which a r e s y s t e m a t i c a l l y high- e r t h a n t h e experimental ones. ( a R/ 3 T) h a s a max-
P
imum a t about xLi = 0.1 and a minimum a t 0.7.
I t i s n e g a t i v e between a b o u t 50 and 80 a t % Mg. An analagous behaviour i s r e p o r t e d by H e i t j a n s e t a l . 2 f o r t h e T dependence of t h e q u a n t i t y ( ~ ~ ~ 1 - l . T1 i s t h e s p i n - l a t t i c e r e l a x a t i o n time. The c o n c e n t r a t i o n
-1/2
dependence of (T T) which shows a s t r o n g anomaly 1
i n L i P b comes o u t t o be l i n e a r w i t h i n experimental e r r o r .
Comprehensive t h e o r e t i c a l work on t h e e l e c t r o n i c s t r u c t u r e and physicochemical p r o p e r t i e s of LiMg a l l o y s h a s b e done by FaberZ1! Beauchamp e t a l . 22) ,
I n g e l s f i e l d l '! LeribauxZ3) and by H a f x ~ e r ~ ~ ! S t a r t i n g from a f r i s t - p r i n c i p l e s o p t i m i z e d p s e u d o - p o t e n t i a l , Hafner could e x p l a i n a number o f p r o p e r t i e s of t h e s o l i d a l l o y s . For t h e l i q u i d , a n a b i n i t i o . c a l c u l a - t i o n u s i n g a system of h a r d s p h e r e s f o r d e s c r i b i n g t h e l i q u i d s t r u c t u r e gave very good v a l u e s f o r t h e e n t h a l p i e s of formation. However, t h e volume con- t r a c t i o n i s s t r o n g e r t h a n i n t h e s o l i d and, a s a consequence, anwrong v a l u e was o b t a i n e d f o r t h e en- t r o p i e o f mixing. The e f f e c t of a n e v e n t u a l chemi- c a l s h o r t - r a n g e o r d e r could n o t b e accounted f o r . W e s e e t h a t t h e r e i s r e a l l y a s t r o n g i n t e r e s t i n s o l i d and l i q u i d LiMg a l l o y s . . B u t s t r a n g e l y en- ough, v e r y fundamental p r o p e r t i e s l i k e d e n s i t y , compressibility and s p e c i f i c h e a t o f t h e l k q u i d a r e s t i l l missing. They a r e p r e s e n t e d i n t h i s p a p e r t o g e t h e r w i t h i n f o r m a t i o n a b o u t t h e c s r o . S u r f a c e t e n s i o n d a t a w i l l b e a v a i l a b l e i n t h e n e a r f u t u r e .
Experimental Procedure
The samples were prepared from 99.9 % Mg and 99.9 8 Li in an atmosphere of dry high purity argon. The volume per atom
V M and the adiabatic compressibility XS were deter- mined as described by Ruppersberg and speicher6! The specific heat C was measured with a Perkin-Elmer
P
DSC-2 apparatus. The neutron diffraction experiments were performed on the D4 instrument at the ILL in Grenoble as described by Ruppersberg and ~ n o l l ~ ! The sample was of the zero-alloy composition7~i
0.7Mgo. 3 and the diffraction pattern yields directly the 'CC (q) partial structure factor. A correction and normalization of the diffraction patterns was only possible assuming a hydrogen content of 1%-
Results and Discussion
The results of the neutron diffraction experiments which are shown in figs. 1 and 2 are discussed fol- lowing the f~rmalism presented by Chieux and
Ruppersberg in these proceedings1) and compared with former results on liquid ~ i ~ g ~ ) and ~ i P b " ~ ) alloys.
The excess stability function, E, calculated from S(o) amounts to 5 and 4 K~al/(~-atom) at 695 and875K
Total neutron structure factors
- 695 K
Fig. 2:
Radial
concentration-
- 6 9 5 K correlation
functions
I . I , . . I
0 2 4 r , (8)
respectively. This is in good agreement with the data deduced from Saboungi and Blander's workla! E is very small compared with the values observed for
LiPb and LiAg at the same composition. The first peak and the subsequent oscillations of SCC(q)/xAxB in fig. 1 are extremely small, but the temperature ef- fect is clearly revealed. The 4 mr 2 pee-curves in-
dicate preferred heterocoordination of nearest neigh- bours. But no well-defined csrois revealed beyond this distance. Assuming a total of ten nearest neigh- bours and a vanishing SNC(q), the csro-parameter 0( 1 becomes -0.04 and -0.035 at 695 and 8 7 5 ~ respective- ly. This is not too different from the value of-0.06 observed at room temperature and at the same compo- sition for the solid phase16! indicating that simi- lar to AgLi the csro persists almost unchanged thro- ugh the melting point. In LiAg and LiPb the csro is much more pronounced ( a l -0.15 for Li Ag at 6ooK)
7 3
and persists, especially for Li8PbZ,overmuchlarger distances. Similar as to the solid phase also in liquid LiMg the distance between unlike nearest neighbourscomesout to be somewhat smaller than the mean value of the pure components, thus indicating non-additive potentials. However, $ (x) , fig. 3, is almost linear. A contraction of 5% as in the solid would have easily been detected. For LiPb and LiAg
v "J'
g-atom . * . 0.
..I
A - 1
l . . . . . . . . a I
Li 50 at% Mg
Fig. 3: Volume per g-atom 0-0 and its relative temperature derivative A-A at 975K
in both phases a strong negative excess volume has been observed. The curves X S ( x ) of the liquid all- oys, fig. 4, deviate strongly from a linear beha- viour. For solid LiMg a much smaller deviation in the same direction has been reported17! Also C (x),
P
c8-598 JOURNAL DE PHYSIQUE
fig. 5, deviates significantly from the mean value of the pure elements. The excess value is larger for the liquid than for the solid alloys. The latter curve might be too low due to slow cinetics. A non- linear behaviour has also been observed for the temperature
10'2cm2 dyn
13 11
9 10'~crn2
dyn.K 5 3 1
Li 50 at% Mg,
Fig. 4: Compressibility: XS A-A , XT a-• (dis- placed by one unit) and (&$/aT) 0-0
liquid
--
CV-2 liquid
.
- - -
31 . . . . . . . . . 4
Li 50 a% Mg
Fig. 5: Specific heat at ROOK: C - e, c v 0-a.
P
(displaced by -2 units) and at 4ooK: C A - A
P
O I . . ' . . . . ' . I
Li 50 at% Mg
Fig, 6: Griineisen parameter for the liquid at 8ooK 0-0 and for the solid phase at 3ooK A - A
derivatives of $ and XS , figs. 3 and 4. v-ldSl/d~
is smaller than the mean value of the pure elements, contrary to what has been observed for the solid phase. As a consequence, the plot of the Griineisen parameter against composition, fig. 6 , looks differ- ent from the solid and the liquid alloys. Finally, we have all the information to calculate for the li-
4 and 5. Tabulated values of the experimental results may be obtained from H. Ruppersberg.
Acknowledgements: The financial support of the ILL, Grenoble,and of the Deutsche Forschungsgemeinschaft are gratefully acknowledged.
References
1. P. Chieux and H. Ruppersberg,these proceedings 2. P. Heitjans, G. Kiese, H. Ackermann, B. Bader,
W. Buttler, K. Dorr, F. Fujara, H. Grupp, A.
Korblein and H.-J. St6ckmann, these proceedings 3. H. Ruppersberg and W. Knoll, Z. Naturforsch.
32a (1977) 1374
-
4. H. Reiter, H. Ruppersbergandw. Speicher, Inst.
Phys. Conf. Sex. 30 (1977) 133
5. H. Ruppersberg and H. Egger, J. Chem. Phys. 63
(1975) 4095
6. H. Ruppersberg and W. Speicher, Z. Naturforsch.
31a (1976) 47
-
7. A.T. Steward, Phys. Rev. 133 (1964) A1651 8. K. Bernd and 0. Briimme, phys. stat. sol. (b)
78 (1976) 47
-
9. M. Ide, J. Phys. Soc. Japan 2 (1971) 1352 lo. G.F. Lynch, M.J. Stott and A.R. Williams,
Solid State Commun. 13 (1973) 1675
11. A.G. Metliewson and H.P. Myers, J. Phys. F 3
(1973) 623
12. P. Kubrca, B.T.A. McKee, A.T. Steward and M.J.
Stott, Phys. Rev. B 11 (1975) 11
13. Y. Tsuchiya and S. Tamaki, J. Phys. F 8(1978)L29 14. J.A. Cattersall and J. Trotter, Phil. Mag. 4
(1959) 1164
15. J.E. Inglesfield, J. Phys. F 9 (1979) 1551 16. F.H. Herbstein and B.L. Averbach, Acta Met. 4
(1956) 407 and 414
17. R.W. Lynch and L.R. Edwards, J. Appl. Phys. 41
(1970) 5135
18. M.L. Saboungi and M. Blander, J. Elektrochem.
5 e i . e (1975) 1631
19. F. Sommer, 2. Metallkde. 2 (1979) 359
20. P.D. Feitsma, T. Lee and W. van der Lugt, Inst.
Phys. Conf. Ser. 30 (1977) 219 -
21. T.E. Faber, Adv. Phys. 16 (1967) 637
22. P. Beauchamp, R. Taylor and V. Vitek, J. Phys.
F 2 (1975) 2017
23. H.R. Leribaux and A.W. Engel, J. Chem. Phys.
68 (1978) 1
-
24. J. Hafner, J. Phys. F 6 (1976) 1243; Inst. Phys.
Conf. Ser. 2 (1977) 102; Phys. Rev. A 2
(19771 352 quid alloys XT and C v , which are shown in figs.
