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KNIGHT SHIFT AND ELECTRICAL RESISTIVITY OF SOME LIQUID LITHIUM ALLOYS
C. van der Marel, W. van der Lugt
To cite this version:
C. van der Marel, W. van der Lugt. KNIGHT SHIFT AND ELECTRICAL RESISTIVITY OF SOME LIQUID LITHIUM ALLOYS. Journal de Physique Colloques, 1980, 41 (C8), pp.C8-516-C8- 518. �10.1051/jphyscol:19808130�. �jpa-00220228�
JOURNAL DE PHYSIQUE Colloque C8, suppZdment au n08, Tome 41, aoiit 2980, page C8-516
KNIGHT SHIFT AND ELECTRICAL RESISTIVITY OF SOME LIQUID LITHIUE? ALLOYS
C. Van der Mare1 and W. Van der Lugt
S o l i d S t a t e Physics Laboratory, Materials Science Center, University o f Groningen, MeZkweg 2 , 971 8 EP Groningen, Netherlands.
Abstract.- In liquid binary alloys of Li with Cd, In, Sn and Pb both the Li Knight shift and the 7 electrical resistivity have been measured as a function of concentration and temperature. Combining the results with existing data on the thermodynamical properties of these alloys it is concluded, that a strong charge transfer occurs from Li to the less electropositive Cd, In, Sn or Pb.
INTRODUCTION. - During the last ten years several liquid alloys of simple metals have been found which exhibit large deviations from metallic beha- viour around some specific composition. Examples are tile systems Ig-Bi, CS-Au, Li-Bi and Li-Pb. In liquid Li-Bi alloys a transition occurs to non-me- tallic behaviour near the composition Li Bi; al- 3 though less pronounced, the same kind of behaviour is observed in liquid Li-Pb alloys: in this system the electrical resistivity peaks up to about 500 yS2 cm at the composition Li4Pb 111. Also the densi- ty, enthalpy of mixing and activity exhibit large deviations from ideal behaviour in these systems
[2]. These effects are ascribed to charge transfer from Li to the less electropositive Bi or Pb, re- sulting in a saltlike mixture near the composition Li3Bi or Li4Pb. If Strong charge transfer occurs, one may expect that this will be reflected in the Knight shift. Therefore we have measured the '~i Knight shift in liquid Li-Pb alloys. Assuming that the difference in workfunction, A$*, of the pure components is a measure for the charge transfer, in the systems Li-Cd, Li-In and Li-Sn the same amount of charge transfer is expected as in Li-Pb
(A$" = 1.20, 1.05, 1.30, 1.20 and 1.30 in Li-Cd,
-In, -Sn, -Pb and -Bi respectively [3] ) . The re- sults of our measurements of the Knight shift in these systems are presented in this paper. Further- more we present resistivity measurements on liquid Li-Cd and Li-In alloys.
RESULTS. - Li-Cd. In figure la both the experimen- tal and the calculated electrical resistivities, p ,
at 550°c, are plotted as a function of concent-ra- tion. The theoretical curves are calculated by
means of the well known Faber-Ziman formula, using Percus-Yevick hard sphere structurefactors, Shaw modelpotentials and different types of screening;
for details we refer to [ 4 ] . (dp/dT) was found to P
be slightly negative for Cd concentrations between 45 and 90 at%; this is in agreement with the dif- fraction model. In figure lb the 7 ~ i Knight shift vs. concentration is plotted. The Knight shift de- creases linearly when Cd is added to Li, whereas
O L ~ 20 u LO 60 80 Cd
cCd (at %I -
FIG. 1. Liquid Li-Cd at 5 5 0 ~ ~ . (a) electrical re- sistivities; -. . experiment; --- . calculated, using different sets of hard sphere structure factors (ref. [ 4 ] ) . ( b ) : '~i Knight shift;
def
AK/K
-
(%i (c) - ICLi (0)) /KLi (01, where %i(0) denotes the Knight shift of pure Li.Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19808130
a change of slope occurs at the 50% Cd composition.
From this behaviour it seems that the 50% composi- tion is of special importance in this system. Un- fortunately the only measured physical quantity of liquid Li-Cd alloys which could be found in the li- terature is the density of the 50% alloy; just above the melting point a volume contraction of 13%
is reported, which increases with increasing tem- perature. For a discussion we refer to [4].
Li-In. In figure 2a the electrical resistivity, p, at 6 5 0 ~ ~ is plotted as a function of composition.
The resistivity exhibits a distinct peak at c = Li 75 at%, whereas the ( d ~ / d T ) ~ is strongly negative at this composition (fig. 2b). In this respect the
FIG. 2. Liquid ~ i - 1 n at 650'~. (a): electrical re-
. experiment; -'---
sistivities; ---' : theory. (b):
temperature derivative of p .
Li-In system resembles the Li-Pb system [I], al- though the effects are much stronger in the latter one. In the Li-Pb system a large volume contraction is observed, with a maximum of 18% at the composi- tion Li4Pb 151. It was therefore interesting to measure also the density Of liquid Li-In alloys.
The measurements were performed using a stainless
steel pycnometer. The highest attainable tempera- ture was 6 0 0 ~ ~ ; therefore no measurements could be done between 40 and 65% In. The measured mean ato- mic volume, a, at 600'~ is plotted in figure 3a.
FIG. 3. (a) mean atomic volume Q in liquid Li-In at 6 0 0 ~ ~ . (b): 7 ~ i and l151n Knight shift vs. con- centration in liquid Li-In.
The volume contraction has a pronounced maximum of 15% at the 25% In composition. Both the strodg volume contraction and the observation that (dn/
dt)alloy < (dR/dt)ideal for all compositions! sup- port the assumption of an ionic mixture. From a li- near extrapolation we obtain an estimate for the size of a Li+ ion in In-rich alloys. A value of about 18 2 3 is found. This is the same value as is found in liquid Li-Pb for c > 20 at% [ 5 ] , and in
Pb
liquid Li-Cd alloys for c > 50 at% (assuming a Cd
linear dependence of on concentration for c >
Cd 50%). The results of our Knight shift measurements on both the 7 ~ i and the l151n nuclei are plotted in figure 3b and discussed in [6].
Li-Pb. The results of our Knight shift measurements are plotted in fig. 4a. The 7 ~ i Knight shift decrea- ses rapidly when lead, upto 20 at% Pb, is added to pure lithium; when more Pb is added K increases somewhat. The behaviour of the Knight shift fits qualitatively well in the model generally accepted:
JOURNAL DE PHYSIQUE
FIG. 4. (a): 7 ~ i Knight shift in Li-Pb alloys at liquidus temperature. (b): temperature derivative of the 7 ~ i Knight shift in liquid Li-Pb.
charge transfer occurs from Li to Pb, resulting in a partially saltlike mixture near the composition Li Pb, whereas the electrical transport properties
4
are determined by a strongly scattered electron gas.
As shown in figure 4b, the temperature derivative of the Knight shift, dK/dt, exhibits a maximum as a function of concentration at the composition Li4Pb.
At the same composition the temperature derivative of the electricalconductivity, d~/dt, has a maximum
[I]. Qualitatively this is in agreement with the prediction K = "'a in the diffusive scattering re- gime. For a more comprehensive discussion of the results we refer to [7].
Li-Sn. The results of our Knight shift measurements in liquid Li-Sn alloys are shown in figure 5 . The same kind of behaviour is found as in the system Li- Pb, although the Knight shift has a deeper minimum and the dK/dt a higher maximum in Li-Sn. From our observation that the rf skin depth in liquid Li-Sn near the 80 at% Li composition is larger than the skin depth in liquid Li4Pb, it may be expected that the electrical resistivity in liquid Li-Sn is high- er near this composition. For a discussion of the results we refer to [TI.
FIG. 5. (a): 7 ~ i Knight shift in Li-Sn alloys at liquidus temperature. (b): temperature derivative of the Li Knight shift in liquid Li-Sn. 7
ACKNOWLEDGEMENTS. - This work is part of the re- search program of the "Stichting voor Fundamenteel Onderzoek der Materie" (Foundation for Fundamental Research on latter - FOM) and was made possible by financial support from the "Nederlandse Organisatie voor Zuiver Wetenschappelijk Onderzoek" (Nether- lands Organisation for the Advancement of Pure Re- search - ZWO).
REFERENCES
[I] J.E. Enderby, J. Physique C 4 , (19741, 309 [2] M.L. Saboungi, J. Marr and M. Blander, J. Chem.
Phys. 68 (1978), 1375.
[3] R. Boom, F.R. de Boer and A.R. Miedema, J.
Less-Common I.Ietals, 46 (1976), 271.
[4] C. van der Mare1 and W. van der Lugt , J. Phys.
F: Metal Physics, 10 (1980) 1177.
[ 5 ] H. Ruppersberg and W. Speicher, Z. Naturforsch.
31a, (1976), 47.
-
[6] C. van der Marel, E.P. Brandenburg and W. van der Lugt, J. Phys. F : Metal Physics, 8 (19781,
T O W *
171 C - van der Marel, W. Geertsma and W. van der Lugt, to J. Phys. F : Metal Physics, 10 (1980)
