Variation of thermopower of alkali metals at high temperatures

We have calculated, in an empirical form, the temperature variation of the thermopower of alkali metals in the 50–300 K region and at their melting points using the finite mean free path correction to the Ziman formulation as suggested by Ferraz and March. The structure factor was evaluated using the phenomenological models of Sharma-Joshi and Krebbs. Three different types of form factors were used in order to give a comparative test of the applied theories. Our results agree to a considerable extent with available experimental results. Finally, we give a brief discussion of some of the factors that could affect the thermopower of the metals investigated.     

Electron work function in alloys with alkali metals

The electron work function in alloys and compounds containing alkali metals, which are of interest for the designing of new photocathode materials and further development of the theory of electron emission, is studied. It is shown that a number of applied and theoretical issues in this field are poorly understood. These are the temperature and concentration dependences of the electron work function in binary metallic systems, the surface activity of components that are inactive in alloys with alkali metals, and some others.     

Electron interactions and the electrical resistivity of alkali metals at low temperatures

The contribution of the electron-electron umklapp scattering processes to the electrical resistivity of sodium, potassium, rubidium and cesium at low temperatures has been evaluated using a simplified spherical Fermi-surface model with an isotropic transition probability. Our values of the electrical resistivity so obtained compare fairly well with the recent experimental values for sodium, potassium and rubidium. Our theoretical results have also been compared with the other available data in the literature due to Lawrence and Wilkins and MacDonald and Geldart.     

Thermal resistivity of alkali metals

The temperature dependence of the thermal resistivity of alkali metals lithium, sodium, potassium, rubidium and caesium is determined within the free electron approximation by using Krebs's model for the phonon dispersion relations. The normal and Umklapp contributions are obtained separately from an improved method following the procedure of an earlier paper. The results of calculations are compared with available experimental information. The theoretical and experimental resistivity curves are found to be of similar nature, but they show considerable disagreement at low and high temperatures.

     

Electrical resistivity of alkali metals

The temperature variations of the electrical resistivity of alkali metals lithium, sodium, potassium, rubidium and caesium are calculated in the free electron approximation and using Krebs's model for the phonon spectrum. The double average over the Fermi surface is evaluated by an improved method due toBailyn and the separation between normal and Umklapp processes is affected in a more satisfactory manner. The results of the calculations are compared with the experimental data obtained at different temperatures. The theoretical resistivity curves for sodium, potassium, rubidium and caesium show satisfactory agreement with experiment, but not in the case of lithium.     

Superconductivity in the alkali metals

At ambient pressure there are 29 elemental superconductors in the periodic table, none of which is an alkali metal. The first alkali metal to become superconducting under high pressure is Cs followed years later by Li. Alkali metals are believed to be exemplary free-electron systems. The fact that an alkali metal becomes superconducting at all is surprising and is a result of the fact that under pressure it shows marked deviations from free-electron behaviour where, counterintuitively, bands narrow and gaps widen. For this reason the alkali metals are among the most interesting systems known to study in high-pressure experiments and superconductivity is one of their most fascinating properties.     

On the nielsen-taylor effect in the diffusion thermopower of dilute alloys

It is suggested that the electron-phonon vertex correction to the electron-impurity scattering gives rise to an additional term in the diffusion thermopower of dilute alloys at low temperatures. The absolute magnitude of the additional term is similar to the Nielsen-Taylor term. The experiment which can detect these effects is investigated.     

On the compressibility of alkali metals

An analysis of experimental P-V-T data for Na and Cs is given in terms of pseudopotential theory. It is shown that for these metals the contribution to compressibility due to the higher-order terms in electron energy practically does not depend on the position of the ions.     

Longitudinal viscosity of liquid alkali metals

Summary The viscosity coefficient entering sound wave attenuation is evaluated for the liquid alkali metals in an ion-electron plasma approach. It is shown that the contribution from electrical conduction, though small, is by no means negligible. The calculated longitudinal viscosity is very close to the measured shear viscosity contribution, the bulk viscosity being expected to be small in the present approach.     

Second harmonic generation from alkali metals

Nonlinear optical constants of the alkali metals, responsible for the second harmonic generation, are calculated using the Drude model. It is found that the electric quadrupole term of the nonlinear polarization is larger than that of a previous theory of Jha by a major factor of ω²_p/ω². By considering a more realstic electron density distribution, we also obtain an additional dipole term due to symmetry breakdown at the surface. The new nonlinear polarization gives the reflected second harmonic intensity in good agreement with experiments.     

Luminescent properties of chromates of alkali metals

T. Shevchenko Kiev State University, 6, Acad. Glushkov Ave., Kiev, 252127, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 239–248, May–June, 1995.     

Elastic properties of nitrates of alkali metals

By a pulsed ultrasonic method we determine the adiabatic elastic moduli of nitrates of alkali metals. We calculate the characteristics of the strength of the interatomic coupling, the Debye temperature, and the lattice energy of the compounds being investigated.     

The Fermi surfaces of the alkali metals

Long before direct experimental studies of the Fermi surfaces of the alkali metals became technically feasible, evidence had accumulated to suggest that their low-lying energy bands are almost free-electron-like. Indeed, the importance of the free-electron model in the development of the theory of metals owes much t o the coincidence that sodium, now known to be the most free-electron-like of all the alkali metals, was the subject of the pioneering cohesive energy calculations of Wigner and Seitz.¹     

Electrical and thermal resistivities of alkali metals

The electrical and thermal resistivities of sodium, potassium and rubidium are computed in the free electron approximation using Bhatia's model of electron-lattice interaction. The normal and Umklapp contributions are obtained separately using the geometry of the reciprocal lattice. The agreement of the calculated electrical resistivity with experiment is satisfactory in the case of sodium and potassium, but not for rubidium. The general shape of the computed and experimental thermal resistivity curve is the same, but they show considerable divergence at low and high temperatures.The authors are grateful to the University Grants Commission, New Delhi, for financial aid, and to the Computer Centre, Roorkee, for providing the facilities of their IBM 1620 computer.     

An equation of state for alkali metals

Semi-empirical equations of state based on Lindemann's law have been developed to determine the pressure (P) dependence of the melting temperature (T_m) of Li, K, Rb and Cs. The basic inputs are Grüneisen parameter and the bulk modulus. T_m–P variations exhibit maximum melting temperature with concave downwards. The maximum in T_m for Cs is found to occur at pressure of 2.2 GPa whereas for Li, K and Rb it falls in the range of 7–9.5 GPa. The predicted values of T_m as a function of pressure, based on the present empirical relation, fit quite well with the available experimental data. The empirical relation can also be used to extrapolate T_m at higher pressure from the values available at lower pressures.