M.A. Haghani

On the minimum size of metallic clusters in a liquid semiconductor system

Use is made of the fact that the NMR Knight shift K can be used as a local, i.e. atomic scale, indicator of whether the electronic state of the atom is metallic or non-metallic. The authors have measured K for the probe atom Bi in the liquid semiconductor system Tl-Te, and find that KBi drops in a narrower range around Tl2Te than either KTe or the susceptibility. Adopting the quasichemical model for the analysis, it is concluded for this system that a Bi atom needs only a very small number of metallic neighbours (either Tl or Te) in order to show the metallic value of K.

Bonding and dynamics in liquid metallic alloys

Abstract The Knight shift K on the constituent atoms in liquid semiconductors, and the quadrupolar nuclear spin relaxation Rq, are discussed as local effects in liquid semiconductor alloys. We start from a quasichemical model for the thermodynamics, and phenomenological assumptions about the hyperfine interactions. The cases of K in AuCs and CsSb, and of Rq in HgK are successfully treated.

Knight shifts in liquid semiconductors

In liquid alloys A-B on the verge of semiconducting state, the Knight shift K(x) on one or the other component deviates strongly from the trend shown by the magnetic susceptibility χ(x), over wide ranges of x. We use Sn-Te (and Cu-Te from the literature) as examples, presenting for the first time data for K of Te on the metal-rich side (Sn1-xTex, x = 10-8...0.5). As an explanation a quantitative connection is proposed between thermodynamic properties ΔH(x), ΔS(x) on the one hand and χ, K on the other, by using the quasichemical model, and by observing the local character of the Knight shift. Good agreement is achieved.

ANOMALOUS BEHAVIOUR OF THE KNIGHTSHIFT ON IMPURITY ATOMS IN GLASS-FORMING ALLOYS

TDPAD (time dependent Perturbation of Angular distribution) technique has been used to measure the Knightshift of69mGe in liquid Ge and the solute Knightshift for73mAs in solid and liquid Germanium and the Ge alloys Ge−As, Ge−Se and Ge−Te. In the Ge−Te alloy the As Knightshift could hardly be explained by the magnetic properties of the alloy. The anomaly is discussed taking the glass forming properties of the Ge−As−Te system into account.

Bond character in liquid alloys from magnetic susceptibility

A model of assumed reactions μ A + ν B η A μ B ν has proven very useful in liquid alloys with strong A–B bonding, where it describes thermodynamics (Δ H , etc.), Knight shifts and quadrupolar relaxation. It is here applied to discuss the contributions to the magnetic susceptibility, made by the right-hand side state of the reaction (A μ B ν ). By combining with a description of the susceptibility as a function of the degree of covalency in crystalline compounds, an estimate of that degree for the A–B bonds in several liquid-metal-Te alloys is derived. Thus it becomes possible to place them on a bond character chart.

Knight shifts and bonding in liquid semiconductors

Abstract The Knight shifts K of both atoms in liquid binary semiconducting alloys are derived, using the quasi-chemical model which had been developed for the thermodynamic properties, and plausible assumptions about the hyperfine interactions. An asymmetric shape for K versus concentration is obtained. Comparison is made with data for K (Te) in liquid SnTe. A strong reduction of K on the minority side appears to be a general consequence, and a sign of local interaction, in strongly bound liquid alloys.

Electron Localization in the Liquid T1-Te-System as Seen by Bi-Impurity

Electron localization is observed in numerous liquid alloys of s-p-metals, e.g. in alloys of Tellurium, at stoichiometric compositions. There they show the property of strong decrease of the magnetic susceptibility X, electric conductivity σ, and Knight shift K as well as strong increase of the viscosity, Hall effect and of the magnetic nuclear spin relaxation rate RM /1, 2, 3, 5/.

The Knight shift of Ge and As in liquid Ge, and in liquid Ge and Ga alloys

The Knight shifts of As and Ge in liquid Ge have been determined by TDPAD (time-differential perturbed angular distribution) measurements over a temperature range of 1210-1370 K, using the isomeric nuclei 73mAs and 69mGe as probe atoms. The Knight shifts have also been measured in liquid Ga (295-1175 K), Ga0.33Ge0.66 (1010-1210 K), Ge0.66Pb0.33 (1170-1215 K) and GaSb (975-1135 K). For both As and Ge the shifts are essentially metallic in these matrices. However, even in definitely metallic conditions for As, the shift is only about 2/3 of that of Ge. Non-metallic references for the Knight shift of 73mAs have been established in liquid GaI3 (515 K) and solid GaAs (1440-1510 K); for Ge reliable reference data were available.

Nuclear Quadrupolar Relaxation and Thermodynamics in Liquid Ternary Alloys

In liquid alloys with strong AB bonding (decrease of electrical conductivity etc. at stoichiometric compositions; for a review see /1/) indications for long living associates have been derived from nuclear spin relaxation /2/. In such systems experimental results show high increase of quadrupolar rate RQ in comparison with the pure metals.

Impurities in liquid semiconductors, studied by TDPAD technique

Abstract Measurement of Knight shift K and nuclear spin relaxation rate by perturbed angular correlation techniques is possible at very low concentration of probe atoms and at high temperatures. Change of K of Ge upon melting, 0.49%, is measured for the first time. For As as an impurity in Ge, this change is smaller than in liquid As.