P. L. Srivastava

Stability of HgNa and HgK liquid alloys

Abstract The alloying behaviour of HgNa and HgK liquid alloys has been investigated by assuming that the chemical complexes Hg2Na and Hg2K exist near the melting point on the molten amalgams. This has been used to obtain the concentration dependence of the free energy of mixing, activity, long-wavelength fluctuations and the volume of mixing. The results reveal that HgNa liquid alloys are more stable than HgK at all concentrations. There is every likelihood of the existence of Hg2Na and Hg2K complexes in the liquid alloys.

Temperature-dependent structure and electrical transport in liquid metals

A simple model has been considered to obtain the reversible temperature dependence of the static structure factors S(q) for liquid metals. The measured values of S(q) near the melting point have been utilised to obtain the same at elevated temperatures for Na, K, Mg, Zn, Al and Pb. The notion of Debye temperature in liquid metals has been discussed. The principal peak heights of S(q) computed at the melting temperature have also been discussed in the light of Verlets freezing rule. The electrical resistivity and thermo-electric power of these metals have been computed as a function of temperature. The success and failure of the Ziman formula have been critically assessed.

Thermodynamic properties of molten LiMg alloy

Abstract The activity, the heat of mixing, the concentration fluctuation in the long wavelength limit (Scc(0)) and the chemical short range order parameter (CSRO) have been studied as a function of composition in LiMg molten alloys by using first order quasi-chemical (QC) theory. The interchange energy has been considered a function of temperature and thus various thermodynamic quantities are calculated at elevated temperatures. The study reveals that though LiMg is considered a simple regular alloy, its various thermodynamic properties deviate from the ideal solution behaviour. Scc(0) computed at different temperatures from QC-theory are found to be smaller than the ideal values and heterocoordination in the nearest neighbour shell is found to exist through the entire concentration range. On the other hand, Scc(0) computed directly from the measured activity data indicates that the LiMg liquid alloy behaves as a segregating system for smaller content of Li (CLi⩽0.3). The building of heterocoordination starts around CLi⩾0.3 and remains for the rest of the compositions.

Harmonic model potential for simple metals

The model potential proposed differs from the Heine-Abarenkov (1964) or Shaw (1968) model potential in as much as it replaces the constant potential in the core region (r<rm, model radius) by a parabolic form. The model parameters are determined by matching the logarithmic derivatives at the boundary (r=rm). The local version of the model potential is used to study the phonon spectra and electrical resistivity of sodium, potassium and rubidium. The calculated results agree well with the experimental values.

Phonon frequencies of caesium and metallic hydrogen

Abstract The logarithmic plots of measured frequencies for different phonon wave vectors, q , with their atomic numbers, N , are found to give a straight line fit. The relation between the frequency v N ( q ) and the atomic number may be approximated by v N ( q ) = N − m C ( q , ϵ ), where m is found to be a constant equal to 0.75 and C ( q ,ϵ) is a constant depending on phonon wave-vector and polarization ϵ. This relationship has been used to predict the phonon frequencies of caesium and metallic hydrogen.

Excess Entropy of Mixing of Equiatomic Binary Molten Alloys

Abstract The Gibbs-Bogoliubov variational method has been considered to understand the alloying behavior of binary liquid alloys. The method has been used to study the entropy(S) of pure liquid metals (Cd, Mg, Zn, Al, In and Tl) and excess entropy of mixing, ΔS xs of binary alloys (CdZn, MgZn, Cdln, CdTl, InZn and AlMg). The effect of electron-ion interaction on S and ΔS xs has amply been discussed. The excess entropy of mixing have been found sensitive to the electron-ion potential. The computed values of S and ΔS xs are in very good agreement with the experimental observation.

Phonon spectrum of lithium

The phonon spectrum of lithium has been computed by Shaws optimized model potential method in the local and nonlocal approximations using the Shaw, Singwi et al and q-independent exchange and correlation factors. It has been found that the nonlocal form of the potential gives better results than the local form.

Phonon frequencies and electrical resistivity of rubidium by the optimized model potential method

The calculated transverse frequencies agree very well with the experimental results but there is some divergence at a few points in the longitudinal branches. The computed value of the electrical resistivity using the exchange and correlation gives a better agreement with experimental values than those obtained by other workers previously reported using the model potential. It has been observed that although the calculated numerical values of the resistivity differ noticeably when the two exchanges and correlations are used, the calculated phonon frequencies differ insignificantly. The disagreement between the calculated and experimental result is considered to be linked with the form of screening used.