Cs Alloys Research Articles

Fermi surface changes and electron scattering anisotropy in alkali metal alloys II. The rubidium-cesium system

The de Haas-van Alphen effect has been used to study the changes in Fermi surface (FS) dimensions and the electron scattering in dilute Rb(Cs) and Cs(Rb) alloys. The initial FS cross-section changes indicate that at each end of the system the actual lattice constant changes lie slightly below a linear interpolation between the host lattice constants. The changes in FS anisotropy are relatively large (up to −10−3 / at % in FS radius for Cs(Rb)): a phase-shift fit with a combination ofs andp terms gives a good representation of the changes in Rb(Cs), but that for Cs(Rb) is relatively poor. The electron scattering has less forward-scattering component than in the K-Rb system, the ratio xρ/x0 between the resistivity temperature and the average Dingle temperature being 0.73 in Rb(Cs) and 0.74 in Cs(Rb). The scattering rate anisotropies are large, 20% in Rb(Cs) and 63% in Cs(Rb). In both cases the maximum scattering rate occurs at 〈110〉. Phase-shift fits give a good representation of the scattering anisotropy at both ends of the alloy system: a combination ofs andp terms appears best for Rb(Cs) and ofs andd for Cs(Rb). However, these phase shifts give poor values for xρ/x0, and no agreement with a lattice-distortion prediction for the Friedel sum.

Electron transport in liquid metals and alloys

This paper deals with a number of selected topics from the field of electric transport properties in liquid metals and alloys. First, some nearly free electron systems are considered; it appears that some problems associated with the properties of liquid Na–Cs alloys and of amalgams are still unsolved. Then, systems exhibiting strong compound formation, particularly alkali–nonalkali alloys with a large electronegativity difference between the components, are reviewed. A qualitative interpretation in terms of chemical-valence rules, based upon our knowledge of the solid state, is given. Next, recently developed theories dealing with transport properties in disordered media are critically discussed. Some models for the interpretation of the alkali – group IV alloys are presented. The basic ideas derived from these models are used also as guidelines for a more qualitative discussion of the alkali – group III and alkali – group V alloy systems.

Partial structures of compound‐forming liquid gold–caesium alloy. A model potential approach

AbstractThe compound‐forming AuCs alloy is studied with a square‐well potential as a perturbation over a hard‐sphere mixture. The partial structure factors S11(k), S12(k), S22(k) and also SNN(k), SCC(k), and SNC(k) are computed at various concentrations and temperatures. Here 1 refers to gold and 2 refers Cs. The total structure factors obtained by the present method agree very well with the measured values. The most important aspect of the computations is the accurate evaluation of the number density of each of the species. Density measurements indicate strong contraction at 50% concentration and it is found to give a subsidiary peak in S11(k) and a high principal peak for SNC(k) at this concentration. The present calculations show that if the correct density measurements and hence the number densities are available, the evaluation of partial structure factors with sufficient accuracy is possible. Also the present calculations show many similarities with the CuPb alloy which also forms a compound.

The Magnetic Susceptibility and Its Temperature Dependence of Liquid Hg–Tl and Hg–Cs Alloys

The molar magnetic susceptibility χ M of liquid Hg–Tl and Hg–Cs alloys was measured from room temperature to 748 K using the Fraday method. The observed χ M of liquid Hg–Tl alloys shows positive deviations from the linear concentration dependence. For liquid Hg–Cs alloys a positively enhanced tendency of χ M is found around 40 at.%Cs, though deviations from the linear law remain to be negative as a whole (“W shape”). Such a concentration dependence of χ M is discussed in terms of the nearly free electron model. Positive deviations or positively enhanced tendencies (“W shape”) of χ M in these liquid Hg alloys seem to be explained by taking into account electron-ion interactions. The temperature coefficient of χ M , or dχ M /d T , is discussed from the point of view of higher order ion-ion correlation effects recently found for some liquid mercury alloys.

Comment on the structures of the liquid–vapor interfaces of Na and Na–Cs alloys

We report the results of Monte Carlo simulations of the liquid–vapor interfaces of Na and of two Na–Cs alloys. The calculations are intended to test, on larger samples and using different geometries, the previously reported stratification of the liquid– vapor interface of a metal. Our results show that stratification of the liquid–vapor transition zone of a metal is independent of sample size and geometry. We also demonstrate how the segregation of one component of an alloy at the surface influences the structure of the liquid–vapor interface, and how the pair correlation function in the liquid–vapor interface of a free cluster depends on the radius of curvature of the cluster.

The Volume of Liquid Hg–Tl and Hg–Cs Alloys

The molar volume and the thermal expansion coefficient of liquid Hg–Tl and Hg–Cs alloys were measured by a picnometer method. The molar volume of liquid Hg–Tl alloys varies almost linearly with concentration, and that of liquid Hg–Cs alloys shows large negative deviations from the linear variation. The thermal expansion coefficient of liquid Hg–Cs alloys shows a slight hump in the dilute Cs concentration range. The concentration dependence of the molar volume of these liquid alloys calculated by a simple pseudopotential approach are qualitatively in good agreement with experiment.

Chemical potentials and related thermodynamic properties of molten Na-Cs and Na-Bi alloys

Reports detailed data on the chemical potential of Na in molten Na-Bi and Na-Cs alloys. The measurements employed an electrochemical cell with beta alumina as the electrolyte. The concentration range was from 0 to 50 at.% Na in Bi and from 20 to 30 at.% Na in Cs. The temperature range was from the liquidus to 600 degrees C in the Bi system and from the liquidus to 150 degrees C in the Cs alloy. The latter measurements were extended very close to the eutectic at -29 degrees C. The Na-Bi system exhibits strong deviations from ideality at all but the most dilute Na concentrations while the Na-Cs system is very close to ideal throughout the range studied.

New crystalline phases of an equiatomic KCs alloy at low temperature

New crystalline phases of an equiatomic KCs alloy at low temperature

Extreme Ultraviolet Absorption Spectra of K–Rb and K–Cs alloys

The optical conductivities of K–Rb and K–Cs alloys have been measured at liquid nitrogen temperature using synchrotron radiation from a 0.4 GeV electron storage ring over the photon energy range from 10 to 30 eV. The spectra of the alloys have the profiles given by the proportional sums of the spectra of pure alkali metals and this feature suggests the localization of the excitation of outer-most p -shell electrons. The critical exponent of the Fermi edge singularity is altered by alloying. Its concentration-dependence is interpreted as indicating that the shape of spikes at the edge is affected not by the density of states but by the size of the core hole. The energy positions of the edge are shifted by alloying. The amount of the shift is dependent on the concentration and increases for increasing atomic number. This, along with the change in the exponent, may be ascribed to charge transfer effects due to alloying.

Chemical potentials and related thermodynamics of liquid Na–Cs alloys

Data on the temperature and composition dependence of the chemical potential of Na in liquid Na–Cs alloys, obtained from an electrochemical cell, are reported. A variety of thermodynamic parameters are calculated. In particular the long-wavelength limit of the concentration correlation function is calculated and used to rule out the existence of Na2Cs. Rather, it is shown that there are long range fluctuations (as at a phase separation) in the vicinity of xNa = 0.80. This incipient phase separation must then be the cause of anomalies in acoustic and other properties reported in the Na-rich portion of the phase diagram.