C. van der Marel

The phase diagram of the system lithium-silicon

Abstract A large number of LiSi alloys with compositions between 5 and 50 at.% Si have been investigated by means of the Differential Scanning Calorimetry (DSC) technique. The results are in good agreement with a number of independently determined liquidus temperatures, and compatible with the compositions of the intermetallic compounds in this system. The phase diagram obtained is slightly at variance with earlier reported ones. It is shown that the latter probably are inaccurate as a consequence of corrosion of the used sample holders.

NEW INSIGHTS INTO THE STRUCTURE OF B2O3 GLASS

Abstract The results of structural investigations of various types of B 2 O 3 glass with different thermal histories are presented. The density and the glass transition temperature T g depend on the cooling rate at which the glass is quenched. For quickly quenched glass (cooling rate 10 3 K/s) the density is 1.79 g/cm 3 and T g is 278°C whereas these values for slowly quenched glass (cooling rate 4 × 10 −3 K/s) are respectively 1.83 g/cm 3 and 298° C. X-ray diffraction and Molecular Dynamics simulations show that the structure of vitreous B 2 O 3 can be explained by a model of randomly connected BO 3 triangles. The slower the glass is quenched, the more the BOB angles of adjacent BO 3 units approach 120°. We have found no tendency of neighbouring BO 3 triangles to form equiplanar complexes if the cooling rate decreases and therefore we have found no evidence for the existence of boroxol rings. The combination of the results of density measurements and X-ray diffraction studies indicates that for the slowly quenched glass the oxygen tend to be out of the plane of adjacent BO 3 triangles. This results in a more densely packed glass structure for slowly quenched B 2 O 3 glass.

STRUCTURAL AND DYNAMICAL PROPERTIES OF SOME LITHIUM BORATE GLASSES

Abstract Structural and dynamical properties of some lithium borate glasses have been investigated by means of X-ray diffraction studies and molecular dynamics (MD) calculations. The structure of lithium borate glasses appears to consist of randomly connected planar BO3 triangles and BO4 units. A comparison of the slowly quenched glasses (studied by X-ray diffraction) and fastly quenched glasses (studied by MD simulations) leads to the conclusion that a small quench rate leads to a preponderance for the B-O-B angles of adjacent BO3 triangles to 120°. The frequency spectra of B-O vibrations in the MD simulations agree qualitatively with infrared transmission spectra.

Experimental results for liquid alkali-group IV alloys

Abstract Neutron diffraction experiments and measurements of the Knight shift and the electrical resistivity are presented for the liquid systems LiSn, NaPb, NaSn, LiGe, KPb and RbPb. They provide strong evidence for compound formation. There are indications for the existence of anion-clusters in all of these systems, except in LiSn.

X-ray diffraction measurements on liquid iodine and some dilute mixtures of KI in I2

Using X-ray diffraction we have determined the structure factor of pure iodine and of a number of dilute mixtures of KI in I2. We show that these liquids exhibit short-range orientational order, adjacent molecules being orient- ed more or less parallel. The intramolecular bond length in pure liquid iodine is 2·70±0·01 A, intermediate between the bond lengths of gaseous and solid iodine. Upon addition of KI the bond length increases, while the distances to atoms in the second and third shell decrease. These effects are related to recent high-pressure diffraction measurements on solid iodine.

Physical properties of liquid Li-Cd alloys and of the solid compound LiCd

The liquid alloys of Li and Cd, the electrical resistivity and the Knight shift have been measured over the entire concentration range. The resistivities can be explained fairly well within the Ziman diffraction model. The Knight shift versus concentration exhibits a sudden change of slope at the composition Li0.5Cd0.5. NMR linewidth measurements on the solid compound LiCd provided evidence for an appreciable mobility of the Li atoms through the lattice; the corresponding activation energy for diffusion is found to be 0.49+or-0.03 eV.

The phase diagram and the electrical resistivity of liquid Na-Ga alloys

Abstract The phase diagram and the electrical resistivity of liquid Na-Ga alloys were studied experimentally. Compound formation in the solid state was observed at 20 at.% and at 37 at.% Na. The latter composition closely corresponds to the stoichiometric compound Na22Ga39, reported recently by Ling and Belin. The present DSC and electrical resistivity measurements do not show the existence of a region of immiscibility around 70 at.% Na. The electrical resistivity ϱ shows a maximum value of 203.9 μΩ cm in the isothermal curve at 560° for an alloy containing 57 at.% Na. In the neighbourhood of this composition, the temperature derivative dϱ dT becomes slightly negative. The values of ϱ and dϱ dT remain within the metallic regime; yet, a description by the diffraction model is complicated by a lack of information on both liquid structure and ion-electron potentials.

8Li spin-lattice relaxation in liquid LiSn and LiSi alloys

Abstract The spin-lattice relaxation time, T1, of 8Li has been measured in a number of liquid LiSn and LiSi alloys, both as a function of temperature and of applied magnetic field. The relaxation rate, 1/T1, in liquid LiSn plotted as a function of concentration exhibits a minimum at about 28 at.% Sn. This is qualitatively explained in terms of electron charge transfer from Li to the less electropositive Sn. Varying the concentration and the temperature, deviations were observed from the relation ση≌ constant (σ denotes the electrical conductivity and η the Korringa enhancement). In liquid LiSi, the spin lattice relaxation rate is a decreasing function of the Si concentration up to approximately 43 at.% Si.

The phase diagram of the system lithium-cadmium

Abstract Liquidus and solidus temperatures of a large number of Li-Cd alloys with compositions between 35 and 100 at % Cd have been determined by means of resistivity measurements and differential scanning calorimetry. The results are partly in disagreement with old literature data. According to our measurements the liquidus, which is bell-shaped, attains a maximum of 544°C for 59 at% Cd.

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-