Table of contents

Various theories are now available for treating binary alloys of different constituent bandwidths within a single site approximation. A comparison of three approaches is given, together with a discussion of the form of the Hamiltonian required to describe the effective medium.

Some results of Liu et al have been inverted to give the spatial dependence of the exchange interaction along the c axis. It is found that the interaction is significant out to at least six lattice spacings.

The results of band mass calculations in white tin made with PW and APW formalisms are presented. The one electron crystal potential parameters were chosen to reproduce the known Fermi surface dimensions and the results prove to be very sensitive to the energy dependence of these parameters.

It is observed that the long wavelength density fluctuations of the conduction electrons are dependent on those of the ions. This implies certain relations between the partial structure factors, which are relevant to the analysis of scattering data. An expression for the compressibility of a pure metal is derived and is shown to yield the Bohm-Staver formula in the free electron case.

Values for splittings of 3d, 4d and 5d bands in some metals in the range Z=29-93 have been derived from photoelectron energy distributions. Comparisons with free atom experimental and theoretical values are made and evidence for crystal field effects on the splittings presented.

Using a realistic band structure, the authors compute some properties for pairs of transitional impurities in copper: density of states, magnetic susceptibility, specific heat (RPA approximation) and interaction energy. Especially they discuss the appearance of magnetism from interactions between impurities.

The Auger electron spectrum of a clean Be surface has been investigated. The changes in the spectrum due to oxidation of the surface have also been observed. A possible interpretation of the oxidized spectrum has been offered, based on the changes in the valence band and the shift in the K level of Be on oxidation.

The electromigration and thermomigration of light interstitials, such as hydrogen in metals, have been examined in terms of the quantum theory of diffusion of Flynn and Stoneham. The pronounced isotope effect observed in the effective charge Z* is shown to come from the differences in the self trapping distortions of the various isotopes. The qualitative dependence of Z* on isotope, host lattice and temperature are correctly predicted. The interstitial contribution to the reduced heat of transport Q* is calculated directly from the quantum theory.

The lattice distortion produced by an isolated vacancy in iron, discrete lattice model. In addition the interaction energies between pairs of vacancies in these metals have been computed as a function of their separation. The lattice model assumes a nonequilibrium pairwise potential which includes interactions out to second nearest neighbours and the calculations are performed in reciprocal space. The asymptotic displacement fields have been compared with the corresponding elasticity results for molybdenum and vanadium.

Atomistic calculations of the core structures of six different nonscrew ¹/₂(111) dislocations lying on a (110) plane have been made using three different central inter-atomic forces. The cores of all the dislocations studied have been found to be similar: planar, confined to a single (110) plane. The results are, therefore, interpreted in terms of a density of the Burgers vector in this plane. The determination of the core structure by both the type of the crystal lattice and assumed interatomic forces is discussed in terms of restoring forces for (110) planes which well characterize the strength of binding in a given crystal structure.

For pt. I. see ibid., 523-36. The Peierls stress of the ¹/₂(111) nonscrew dislocations was calculated. Two methods were used: positioning the dislocation in various crystallographically nonequivalent positions and calculating the corresponding variation in its core energy, and simulation of the dislocations in a crystallite subject to an applied shear stress. In the latter case the changes of the core under the external stress were followed. Both methods give similar results which suggests that the changes in the core are not of great importance. Comparison with the screw dislocations and possible implications of the results for the plastic behaviour of b.c.c. metals are then briefly discussed.

Recent calculations of the energetics of divacancy formation and migration in sodium indicate that the most stable divacancy configuration consists of two vacancies at second nearest neighbour sites (2n divacancy) and that the most probable migration steps are exchange jumps between 2n and 1n divacancies and between 2n and 4n divacancies. This complicated migration mechanism involves three different divacancy configurations and two different saddlepoints. In this paper the results of a calculation of the diffusion coefficient, correlation factor and isotope effect for a divacancy mechanism of self diffusion are reported and briefly discussed. Since the divacancy migration involves more than one saddlepoint the correlation factor and the isotope effect are in general temperature dependent.

The positron partial annihilation rates near the Fermi surface in the alkali solid and liquid metals are calculated by using second order perturbation theory for the temperature dependent Green function, including the ionic density correlation. In both cases, solid and liquid, the contributions from the Coulomb interactions to the enhancement factors are assumed to be constant. An Ashcroft pseudopotential is used for the electron-ion interaction, while a selfconsistent potential model is used for the positron-ion interaction within the framework of the pseudopotential model. The calculated annihilation rates are compared with the experimental data for Na and Rb through the counting rate curve.

A new approach to the analysis of positron annihilation long slit angular distributions is presented. The analysis, which provides a more direct measure of the Fermi surface profile, is applied to data for Cu and the results are found to agree well with the computed surfaces of Roaf and Halse. The same analysis provides a guide to the form and intensity of that part of the angular distribution arising from the annihilation of electrons occupying states in the filled Brillouin zones.

A first principle calculation for frequencies of phonons propagating in three symmetry directions in metallic Li is presented. The ion-electron interaction potential is constructed entirely from the Slater type of atomic core orbitals. The results obtained on the Hartree field and Hartree-Slater potential reveal the importance of core-valence exchange potential to predict the cross-over between longitudinal and transverse phonon branches in the ( zeta 00) direction.

Calculations of the electrical resistivity and thermopower of the noble metals and nickel are presented. They are based on a model similar to the simple nearly free electron model used for the liquid transition metals. The scattering of the Bloch functions is described by the t matrix of a single muffin tin potential. The positive sign of the thermopower of the noble metals can be explained in terms of the magnitude of the backward scattering cross section using an argument similar to that applied in the liquid case. The peculiar shape of the Fermi surface need not be invoked in order to explain this sign.

Various inadequacies and inconsistencies of previous treatments of heat flow in a nonequilibrium superconductor are pointed out. The energy current associated with a quasistatic time-dependent order parameter is calculated near the transition temperature using standard techniques and a result obeying the equation of continuity is obtained. Further microscopic calculations indicate the existence of local temperature gradients which drive the entropy current. An attempt is made to calculate corresponding additional terms in the time-dependent Ginzburg-Landau equation.

Measurements of the magnetic susceptibility of polycrystalline and single crystal holmium in the temperature range 293-873 K are reported. Departures from Curie-Weiss behaviour are found below 473 K. Above 473 K, the 1/ chi against T curves are linear to experimental accuracy and give values for the effective magneton number within 0.3% of the free ion value 10.61. Anisotropy in single crystal holmium persists to the highest temperature reached (873 K) and is consistent with the known behaviour at lower temperatures.

Describes a method for calculating the d electron generalized susceptibility for a transition metal which takes full account of the multiplicity of the band structure. It is assumed that the band structure can be represented by a model Hamiltonian and that electrons interact only when occupying the same atomic cell and then only when in d orbitals. The random phase approximation is used. A magnetic instability criterion is derived. This criterion is applied to a discussion of the magnetic instability in gamma manganese.

Measurements of the field dependence of the ultrasonic attenuation of longitudinal sound waves in the frequency range 10 MHz to 300 MHz propagating in the transverse spin density wave phase of a single Q single crystal of chromium interpreted in terms of a relaxation model for thermally activated polarization domains and provide an independent indication that their volume in this sample is of the order of 10^-15 to 10^-16 cm³.

A series of LiMg alloys has been studied by ultra high vacuum ellipsometry. The b.c.c. alloys containing more than 30% Mg show pronounced parallel band absorption and values of the energy gap at the (110) zone boundary are accurately derived. The optical properties of these concentrated disordered alloys show convincingly that the concepts of Fermi surface and zone structure maintain their significance in such disordered systems. The optical and soft X-ray data for Li are used to obtain a qualitative description of the band structure of this metal. The virtual crystal model is applied to the alloy data and found to give a rather poor description of the observed behaviour.

Dispersion curves of four hexagonal metals Be, Mg, Ho and Tl have been obtained on the basis of a modified Sharma-Joshi model. Agreements with experimental measurements are fairly good in two cases namely Be and Mg but not so good in the other two. However the dispersion curves in the (0001) direction are obtained in almost exact agreement with the experimental ones and the deviations which are largest at the zone boundaries in the (0110) direction are in general not more than 15 per cent.

Results of Mossbauer measurements on dilute Fe based alloys with all soluble transition impurities are given; the spectra are analysed to obtain hyperfine field and isomer shift changes at first, second and average further neighbour shells. The hyperfine field changes are shown to be consistent with a model in which the conduction electron polarization has a linear response to the d moment changes induced by the impurity. The isomer shift changes are ascribed primarily to variations in the d spin up density at the Fe neighbour sites.

Gd-Ag alloy thin films have been prepared by vapour quenching on to substrates at 4.2 K, 77 K and room temperature. The formation of alloys has been verified by X-ray diffraction, ESR studies and microprobe analysis. Curie temperatures have been inferred from ESR studies. Over the composition ranges investigated there has been found a marked difference in variation of Curie temperature and g factor with composition for the low temperature and high temperature deposition. X-ray diffraction studies have shown that the Gd rich alloys are amorphous and that precipitation into the constituent elements occurs on annealing. An empirical relation for the temperature dependence of the ESR half power half line width in the paramagnetic region has been derived.