Table of contents

The migration energies of substitutional impurity atoms based on the vacancy mechanism in cubic metals have been formulated in terms of the pseudopotential theory. Calculations have been carried out for fifteen kinds of impurity atoms in aluminum.

The vibrational spectrum of a densely packed metallic glass is discussed in terms of a simple but realistic force constant model. It is concluded that the shape of the spectrum is largely determined by the short range structure and is sensitive to triangles of bonds between near neighbours.

As the vacancy migration rate becomes higher than the positron annihilation rate at sufficiently high temperatures, the effect of vacancy migrations must be taken into account. The modified positron trapping model, with this included, yield values of 0.9 eV for vacancy movement activation energy, and 0.2 eV for divacancy binding energy in Cu.

The electrical resistance of a number of Ni-Cr alloys with compositions between 6 and 15 at.% Cr has been investigated between 1.2 and 300K. The temperature dependence of the resistance is found to be anomalous for compositions close to the critical value for ferromagnetism but it is concluded that there is no evidence of spin disorder scattering above the ordering temperature.

The electrical resistivity of pure aluminium specimens, subjected to varying amounts of cold-work, was measured from 2 to 70K. Although rho ₀, the residual resistivity, increases monotonically with cold-work, the temperature dependent resistivity is very unusual in that it decreases in magnitude and at the same time increases in temperature dependence as rho ₀ increases.

The Hall coefficient of expanded liquid caesium in the density range 1.9-1.1 g cm^-3 exhibits a nearly free electron behaviour, providing evidence for a relatively long mean free path even at reduced densities.

The dispersion relation for the interaction between helicons and phonons for parallel wave propagation along any general direction inside a metal has been derived.

The three partial interference functions of a Co-P alloy, which are simply related to the static pair-correlation functions, have been determined using a polarized neutron technique which may be extended to other binary amorphous ferromagnets. The equations necessary for the interpretation of the measurements are presented and discussed.

The valence band densities of states of Cd, Cd₃Mg, Mg₃Cd and Cd_0.12Mg_0.88 have been studied using X-ray photoelectron spectroscopy. The spin-orbit splittings of the 4d levels have been obtained by fitting model spectra to the data and it has been found that the spin-orbit splitting decreases steadily with Cd concentration until in Mg₃Cd and Cd_0.12Mg_0.88 the free atom value is reached.

The framework of generalized hydrodynamics is used to explore the softening of shear modes and the diffusive mode observed in the phonon spectrum of beta tungsten structures. Due to the fact that the movement of the d electrons is restricted to quasilinear chains and that the number of d electrons in each chain is quasiconserved in the temperature regime above the Martensitic phase transition, it can be expected that fluctuations of the charge density exhibit hydrodynamic behaviour resulting in a diffusive mode. Plausible assumptions about the d electron lifetime lead to a width of the central peak which lies within the experimentally found upper bound for it.

Conformal solution theory applies to some binary alloys, for which the volume differences are not too large. The volume ratio r for Cs/Na=3, and the system is not conformal. A theory of the concentration fluctuations, valid for large r, is described. The liquidus curves are calculated, there is a rather flat portion around an Na concentration of 0.8, correlating with a strong peak in the concentration fluctuations around this composition. This is in agreement with observation. Na-Rb alloys and a number of other alloy systems show a similar feature, and these are briefly discussed.

It is shown that the variation of the Debye-Waller factors of silver, gold and lead with temperature can be described by means of the nearest neighbour central force pair interaction theory of Killean. Expressions for the temperature dependence of the Debye temperatures of six cubic elements are obtained from previous X-ray and neutron diffraction measurements, and the anharmonic pair potential has been derived in each case.

The X-ray emission spectra of free electron metals are calculated as functionals of the many body threshold exponents of Nozieres and deDominicis. The final state interactions are treated in a screened exciton approximation using a selfconsistent Hulthen screened electron-hole interaction determined from the threshold exponents alpha _l. For L_2,3 threshold exponents alpha ₀>or approximately=0.15, the emission is markedly non free electron like. Thus, for free electron metals, these calculations indicate that the exponents fall in the range 0<or= alpha ₀<or approximately=0.15, 0<or= alpha ₁<0.05; such values are to be contrasted with previous theoretical predictions alpha ₀>or approximately=0.4, alpha ₁<0, and with experimentally determined exponents alpha ₀=0.26, 0.18 and 0.15 for Na, Mg, and Al respectively. The implications of these results for the theory of X-ray excited states of metals are discussed.

It is suggested that, contrary to general assumptions, there is a preponderance of f character in the valence band of alpha '-Ce. The approach used is that previously applied to the early actinide metals. It is shown that melting point correlations and selfconsistent APW band calculations yield similar f electron occupation numbers for alpha '-Ce and gamma -Ce and similar principal bonding electron numbers for alpha '-Ce and alpha -U. The latter correspondence makes the fact that alpha '-Ce and alpha -U possess the same crystal structure more understandable.

Observations of magnetoacoustic giant quantum oscillations in the attenuation of 9 GHz shear waves propagated along the b axis in a Ga single crystal are reported. It is suggested that these oscillations may arise from Delta n=+or-1 inter level Landau transitions, and the dominant periods reported here are due to non external Fermi surface cross sections.

Results of calculations based on the KKR method, using a k dependent potential, are presented for Ca. A sufficiently large overlap of the first and second bands, at normal pressure, can be obtained by means of suitable parametrization of KKR method phase shifts. These are compared with those given by Gaspar like potential, having varying amounts of exchange energy. An l dependent Gaspar like potential is used to calculate normal pressure Fermi surface, and symmetry point eigenvalues. The widths of occupied and unoccupied d like states of 0.35 eV and 7.51 eV agree well with photoemission measurements. Calculations of effect of pressure indicate that Ca changes from metal to semimetal at compressed to normal volume ratio is 0.708, the experimental value being 0.67.

A renormalized free atom (RFA) model has been extended to calculate the momentum density for the angular correlation of positron annihilation radiation (ACPAR). Recent measurements of the Compton profiles (CP) and ACPAR of Ni and Cu have been analysed by the RFA model. It is found that the RFA model gives a good overall description of the CP data for Ni and Cu and for Ni it supports an electronic configuration closer to 3d⁹4s¹. As far as the ACPAR data is concerned, the RFA model does not give an equally satisfactory description of the results. It is suggested that band structure calculations, which give a better agreement with the ACPAR results, are essential to describe positron annihilation data.

The quasiparticle energy bands in Al are calculated, with emphasis on development of a general band calculation scheme. The first order, dynamically screened exchange approximation of the self energy appearing in the quasiparticle equation is used for the exchange and correlation contributions. This approximation is simplified by separating it into a Hartree Fock core valence exchange potential, a valence valence exchange correlation potential, and a core polarization potential. The Coulomb potential is calculated in the muffin tin approximation from a charge density determined by a self consistent Kohn Sham calculation, using a modified KKR program. The results indicate that, although non muffin tin effects can be as large as important correlation effects, occupied levels in Al can be found from a priori theory with a relative accuracy of 0.1 eV.

New Hall effect experiments on Al containing Zn, Mg or Ge impurities are discussed and compared with previous experiments on Al containing Frenkel defects; interstitials and vacancies. The low field Hall coefficient is found to change always in the positive direction, with respect to its strong negative isotropic value, this effect being largest for Ge doped Al and Frenkel defect Al, where even a positive sign for Hall coefficient is obtained. Kohler rule investigations show that anisotropic scattering of electrons on point defects is the origin of this effect. The relaxation time anisotropies are explained as originating from corresponding strong differences of the wavefunctions involved. This is proved by OPW charge density calculation for k states on the realistic Fermi surface of Al. The symmetrized results, as contour plots, show strong, expected differences. A simple qualitative measure of anisotropy is derived for both impurity and Frenkel scattering.

Some aspects of the Hartree-Fock approximation as applied to the Anderson model of a degenerate magnetic impurity are studied. Special attention is given to the van Vleck contribution to the susceptibility in a crystal field. A systematic method of solving the selfconsistent equations is given.

The resistivity and thermopower of a sample of gold containing initially 13 ppm Fe have been measured as a function of Fe concentration. This was systematically reduced by a treatment with chlorine at 800 degrees C. For each 4 h treatment time the Fe concentration decreased roughly by a factor of 10. In 16 h the concentration had been reduced from 13 to 10^-3 ppm, the resistivity from 14.4 to 4.0 n Omega cm and the thermopower from -7.2 to +0.03 mu V K^-1. The transition from a typical dilute magnetic alloy to a typical pure metal has been followed in detail and agreement with single impurity Kondo effect theory is good.

Some magnetic properties of ACo₂ compounds, where A is a heavy rare earth metal, are shown to be related to properties of YCo₂. In particular the existence of first order transitions for A=Er, Ho, Dy, but second order transitions for A=Tb, Gd, implies a special temperature dependence of the Landau parameter B which appears in the expansion of the free energy of YCo₂ in powers of the magnetization. B changes from negative to positive with increasing temperature and this is verified experimentally by measurements of the field dependence of the susceptibility of YCo₂ at 4.2, 77 and 300K in field up to 150 kOe. It is estimated that an applied field of about 1400 kOe would be required to produce itinerant electron metamagnetism in YCo₂ and the magnetization of Gd_xY_1-xCo₂, where the 'applied' field is the molecular field due to Gd moments, is discussed from this point of view. Stoner theory is used to relate the behaviour of B to the existence of a maximum in the susceptibility of YCo₂ as a function of temperature.

A general analysis of the nuclear acoustic resonance mechanisms in conductors is given. It is shown that the independence of the observed line shape from the band structure comes from the simplicity of the mechanism of the Alpher-Rubin effect which is solely due to the Faraday induction law; this explains the success of crude electronic models. Furthermore, another coupling mechanism coming from transition metal paramagnetostriction is proposed. Finally, the apparently emitting character of the absorption shape is shown to be related to the need for spin renormalization to take into account the screening of the precession magnetic field by conduction electrons.

It is shown that the quasi irregular behaviour of the boiling points of the rare earth metals is due to the divalent free atomic configuration found for many of these elements. By application of Trouton's rule the author undertakes a quantitative study of the boiling temperatures.