W Geertsma

ELECTRICAL RESISTIVITIES OF LIQUID ALKALI LEAD AND ALKALI INDIUM ALLOYS

Measurements of the resistivities of liquid K-Pb, K-In, Li-Pb and Na-In alloys are presented. The resistivities of the lead alloys exhibit a sharp peak at cPb=21 at.% for Li-Pb and at cPb=49 at.% for K-Pb. This is in agreement with the transition from simple ionic behaviour in Li-Pb to poly-anion formation in K-Pb. The maximum resistivity of K-Pb distinctly exceeds the range of metallic conduction. In the indium alloys the resistivity maximum is less pronounced and the theoretical description is more complicated.

Structure of liquid Na-Sn alloys

Neutron diffraction measurements of liquid Na-Sn alloys provide evidence for appreciable ordering in the liquid. At small Sn concentrations (about 20 at.%) the liquid is similar to a simple ionic mixture with maximum distance between the negatively charged Sn atoms. At higher Sn concentrations, the Sn atoms tend to form aggregates, perhaps in the form of tetrahedra of covalently bonded Sn atoms. Elements of the solid structure seem to be preserved in the liquid state.

Electronic structure and charge-transfer-induced cluster formation in alkali-group-IV alloys

In this paper the authors apply model tight-binding calculations to the electronic structure of systems in which there are essentially two covalent interactions: the intracluster interaction U and the intercluster interaction V. The atomic structure is simulated by a modified Bethe lattice which incorporates closed loops as a possibility. The ratio alpha =V/U is an important parameter to be varied. At a distinct value, alpha crit, a metal-non-metal transition takes place. The results are applied to the electronic structure and chemical stability of anion cluster in liquid and solid alkali-group-IV alloys. The physical parameters which govern the process of clustering are discussed.

LI-7 KNIGHT-SHIFT OF LIQUID LI-PB AND LI-SN ALLOYS

The 7Li Knight shift has been measured in liquid Li-Pb and Li-Sn alloys through the entire concentration range and at several temperatures. The Knight shifts in liquid Li-Pb are discussed together with the electrical conductivity and the spin-lattice relaxation time T1, which also exhibit anomalous behaviour near the composition Li4Pb. The results support the assumption of a partially salt-like mixture around the composition Li4Pb.

THE LI-7 KNIGHT-SHIFT OF LIQUID LI-GE ALLOYS

The 7Li Knight shift in liquid lithium-germanium alloys has been measured through the main part of the composition range. The results, particularly those obtained close to the liquidus, indicate both charge transfer and the formation of homopolar compounds in the liquid.

The 7Li Knight Shift of Liquid Li-Au Alloys; Properties of the Solid Compound LiAu*

Measurements have been performed of the Li Knight shift of liquid Li-Au alloys, both as a function of composition and of temperature. The Knight shift decreases markedly when Au is added to liquid lithium, and is practically independent of temperature. The results are in agreement with a simple tight-binding model in which Li 2s, Au 6s and Au 6p states are taken into account. Additionally, some attention was paid to the solid equiatomic compound LiAu. The ^Li Knight shift and UPS spectra were measured at room temperature. The results are compared with recent band structure calculations on LiAu. Introduction During the last ten years the liquid alloy system Cs-Au has been subject of much interest HI. In this system a metal-nonmetal transition takes place about the equiatomic composition. Recent tight-binding calculations /2,3/ demonstrated that both electron charge transfer from Cs to the much more electronegative Au and the relatively narrow partial Au s band in the equiatomic alloy are essential for this MNM transition. In liquid LiAu the Au partial bands are expected to be broader because the Li atom is smaller than the Cs atom. Indeed, tight-binding calculations * Presented at the Sixth International Conference on Liquid and Amorphous Metals, Garmisch-Partenkirchen, FRG, August 24 to 29, 1986. 10.1524/zpch.1988.156.Part_2.569 Downloaded from De Gruyter Online at 09/28/2016 11:01:46PM via Université Paris Ouest Nanterre La Défense 570 Van der Marel et al. on liquid Li-Au alloys predicted that this system is metallic for all concentrations /2,3/. This prediction finds some support in the observation that the electrical resistivity of equiatomic liquid LiAu is definitely within the metallic regime /4/. We investigated the validity of the aforementioned tight-binding calculations more extensively by measuring the 7Li Knight shift in liquid Li-Au alloys, as it gives information about the character of the wave functions at the Fermi level. The solid equiatomic alkali-gold compounds exhibit interesting properties as well: LiAu is definitely a metal whereas CsAu is a semiconductor (references in 151). We measured the ^Li Knight shift of LiAu at room temperature. Furthermore we performed UPS (ultra-violet photoemission spectroscopy) measurements on LiAu as it provides a picture of the band structure which can be compared directly with the calculated density of states of /5/. Experimental, results and discussion For a description of the techniques used for the Knight shift measurements above room temperature we refer to /6/; LiF was used as reference material. For the Knight shift measurements at room temperature a dilute LiCl solution was used as reference material; the chemical shift of the Li+ ions in this solution is negligible 111. The apparatus used for the UPS measurements is described in 181. The 7Li Knight shift K of liquid Li-Au alloys is plotted as a function of concentration in Fig. 1. The total experimental error is estimated at ± 3 ppm. Within the investigated temperature range, typically from 600°C to 750°C, no temperature dependence was observed. The total density of states at the Fermi level N(E,,) of liquid Li-Au is F calculated as a function of concentration in 12/ using a tight-binding model in which Li 2s and Au 6s states were taken into account. We repeated these calculations using the same values for the parameters and determined also the partial density of states at E ,N.(E ) (i=Li or Au). Assuming a random distribution of the atoms, i.e. short range order parameter a = 0 (definition of asr in /9/), and assuming 19/ that the 7Li Knight shift is proportional to N . (E„) we obtained, by scaling to the L l r experimental Knight shift of pure liquid Li at 600°C, the dotted curve in Fig. 1. The concentration dependence of the calculated Knight shift is rather different from the experimental data. Using the self-consis10.1524/zpch.1988.156.Part_2.569 Downloaded from De Gruyter Online at 09/28/2016 11:01:46PM via Université Paris Ouest Nanterre La Défense Li Knight Shift of Liquid and Solid Li-Au Alloys 571 tently determined values of agr from 12/ we obtained, within 10%, the same results. In order to investigate the origin of this discrepancy we carried out a similar calculation in which also the Au 6p energy level was included. Energy levels and hopping integrals were adopted from 12,91. The Au s-p splitting was taken from atomic spectroscopy data /10/. N .(E ) was calculated as a function of concentration for a =0 (ran-