Table of contents

The surface entropy of liquid metals is calculated by applying the hard-sphere model to the surface of a liquid with the density profile of step function type. The resulting values are at least reasonable to the zeroth-order estimation.

In the light of recent experimental studies on ion implantation in beryllium metal, some of the properties and interactions of implanted lithium, magnesium and zinc have been calculated using effective ion-ion potentials constructed by pseudopotential methods. It is shown that there is a strikingly small interaction energy for Li in Be, with the result that Be is highly transparent to Li ions. The diffusion energy of Li in Be is shown to be much smaller than the self-diffusion energy of Be. It is demonstrated that these properties can lead to a quite plausible mechanism to explain the anomalous lattice sites observed for ion-implanted Li in Be.

The authors have shown experimentally using the ion beam channelling lattice location technique, that lithium atoms ion-implanted into single-crystal beryllium metal occupy substitutional sites. This result disagrees with expectations based on considerations of chemical potentials and local electron densities. The disagreement is thought to arise from a dependence of the final lattice site of Li upon the ion implantation process itself. It is argued that there is a high probability for the capture of Li by a Be vacancy created by the Li as it comes to rest and that, under these conditions, a substitutional site for lithium in beryllium is probably.

The temperature dependence of the electrical resistivity of four CoGa alloys with a partial substitution of a 3d transition metal for Ga is reported. Both the magnitude of the measured resistivities ( approximately 200 mu Omega cm) and their variation with temperature are observed to be very similar to those of certain metallic glasses, with alpha ( identical to (1/ rho )( delta rho / delta T)) being small but negative for all four alloys. The results are found to be well explained by the inclusion of the temperature dependent Debye-Waller factor in the standard expression for the resistivity, this being the first time this factor has been shown to be of importance in a crystalline metallic system.

Accurate measurements of the thermopower of lead at temperatures up to 50K are reported. It is found that in the region 7-12K existing scales are in error by up to 30 nVK^-1 and that the use of lead as a standard material introduces considerable variability from sample to sample. It is recommended that, for the most precise work, the sample of lead should be calibrated in situ against a superconductor.

The spin wave theory of Bhattacharjee et al. (1978) in an asperomagnetic alloy is extended to include the short range order effects existing in amorphous systems.

UPS spectra of (111), (100) and (110) faces of Fe single crystals have been measured at normal electron emission, with HeI (21.2 eV) and HeII (40.8 eV) radiation. The spectra are very similar indicating that one is measuring a density of states rather than direct transitions. The reasons for this behaviour which contrast with that found in the noble metals and Ni are discussed.

The structure of a two-component metallic glass (Mg₇₀Zn₃₀) is described by a relaxed model structure of 800 atoms. The authors use realistic pair potentials calculated from general nonlocal pseudopotential theory, and periodic boundary conditions. The cluster has been given the shape of a regular rhombic dodecahedron, the most sphere-like space filling body. The homogeneity of the cluster is tested by the calculation of the spectrum of Einstein frequencies. The total and the two partial pair distribution functions, the corresponding structure factors S(k) and the dynamical structure factor S(k, omega ) for longitudinal and transverse waves for a whole series of k vectors are calculated. S(k, omega ) allows the determination of the range of reasonably well defined dispersion relations.

The formation parameters of vacancies in hexagonal zinc single crystals have been investigated by combined lattice parameter change and length change measurements. A maximum vacancy concentration at melting temperature of (C_v)_max=(4.9+or-0.3)*10^-4 was found. The energy of formation and the entropy of formation for a single vacancy were determined to be E=(0.53+or-0.07)eV and s=(1.1+or-1) k_B respectively. The creation of vacancies leads to a highly anisotropic volume change in zinc crystals. The ratio obtained from measurements in the a and c directions is ((^{Delta L}/_L)_c-^{Delta c}/_c)/((^{Delta L}/_L)_a-^{Delta a}/_a)=5.7. Six times as many etch pits were found on a surface as on c surfaces. The authors concluded that in their zinc crystals, dislocations were preferentially oriented in the basal plane.

For pt.I see ibid., vol.6, p.1039 (1976). A formalism, based on the use of pseudopotentials and the Gibbs-Bogoliubov inequality on the Helmholtz free energy, is presented for the investigation of thermodynamic properties and order-disorder transitions of binary alloys. Application of the method to Mg₃Cd and MgCd₃ shows that the effect of lattice vibrations can account for about a quarter of the difference in the observed order-disorder transition temperatures of these two alloys. The thermodynamic properties of Mg₃Cd have been calculated for a wide range of temperatures and the results are in satisfactory agreement with experiment.

The calorimetric and magnetic properties of gold-nickel alloys have been investigated over the complete concentration range. The parametric region (x<35% Ni) is followed by a critical-concentration region (35<or=x<or=52.5) and then by a ferromagnetic region (x>or=55% Ni). The paramagnetic and ferromagnetic regions can be discussed within a band model. The critical-concentration region is characterised by peculiar calorimetric and magnetic properties which can be explained by magnetic clustering. A consistent understanding of the onset of ferromagnetism is obtained in terms of cluster interactions.

The Hamiltonian for the ions of a metal can be separated into (i) a structure-dependent part involving all Fourier components of the pseudopotential except the zeroth and (ii) a volume (structure-independent) part to which the zeroth component contributes. For a specified volume, part (i) alone describes the entropy. In earlier work, it was shown that when the observed volumes are used as input information there exists a set of suitably parametrised empty-core pseudopotentials which can be used to calculate the entropies of pure liquid metals and their entropies of mixing. To calculate volumes, both parts (i) and (ii) are needed. It is shown that the pseudopotentials used earlier can be supplemented by nonlocal zeroth Fourier components so as to achieve satisfactory volumes, bulk moduli and thermal expansion coefficients in the pure liquid metals as well as semiquantitative agreement for the excess quantities on mixing.

An experimental study of the propagation of magnetoplasma waves in pure Bi and in semimetallic BiSb alloys at 300 GHz is presented for magnetic fields up to 65 kG. The magnetic field is parallel to the sample surface and perpendicular to the E vector of the incoming high-frequency wave. Alloys in the range from pure Bi to a concentration of 2.35 at.% Sb are considered. Both binary sample surfaces as well as trigonal sample surfaces are examined for a magnetic field direction along each of the main crystallographic axes. From the experimentally determined dispersion curves for the magnetoplasma waves the magnetic field value at which the electrons enter the quantum limit is deduced, and the mass density function f_{alpha alpha} ^j(B) is found. A possible variation of the lattice dielectric constant epsilon ₃ with Sb concentration is suggested. The experimental results indicate that the classical Alfven dispersion is not always obeyed.

Three expressions for the local density of states are examined. The formalism is applied to a bulk Cu atom embedded in a complex constant potential. The results for the several expressions resemble each other very well, in contrast with the results for Cu mentioned elsewhere.

The possibility of obtaining a self-consistent solution for the single-particle Green's function in random binary alloys within the coherent potential approximation is considered. It is shown that the present approach leads to a first-principles approximate definition of the matrix elements of the single-particle Hamiltonian even in the tight-binding case, obtaining a physical ground for such an approach.

The de Haas-van Alphen effect has been measured in the ordered alloy beta '-AuMg. The relativistic LMTO bandstructure has been calculated and predicts a Fermi surface in good agreement with experiment. Both bandstructure and Fermi surface are similar in those of other beta brasses with the same number of conduction electrons per unit cell, with the exception of an additional set of electron ellipsoids in an extra conduction band, which owe their existence to the relativistic lowering of the Au 6s band.

New experimental data of lattice constants, residual resistivities and magnetic properties (magnetisations and hyperfine fields at phosphorus and iron atoms) are presented and discussed in relation with the electronic structure of phosphorus as dilute impurity in an iron matrix; most of them are in agreement with the appearance of '3sp' virtual bound states near the Fermi level. The iron hyperfine field values compared with those measured in more concentrated amorphous alloys show in both systems a typical dependence with the number of phosphorus atoms as nearest neighbours. A comparison of the whole data with those obtained for other 'sp' substitutional impurities of the same periodic table row (Al, Si) or column (As, Sb) points out the role played by the valence and the period of impurity on the investigated properties.

The canonical and LMTO band methods have been used in self-consistent band calculations on 27 A15 compounds. The calculations are described and the basic results, in the form of density of state diagrams and charge analyses for each compound, are presented.

The density of states and the electrical conductivity of concentrated transition metal alloys is calculated, using an extended Hubbard model. Due to the combined influence of chemical disorder, electron-electron correlation and s-d hybridisation the conductivity varies strongly with the electron density n. Especially at high densities of states in the d band the scattering processes of the s electrons into the d band reduce considerably the magnitude of the conductivity. By that a qualitative agreement with experimental observations results. Considering the modification of the Fermi distribution function and of the density of states by changing the temperature, a contribution to the temperature dependence of the conductivity is obtained.

Hall resistivity measurements in the temperature range 100-800K have been used to study the influence of thermal cycling and annealing on amorphous Fe₄₀Ni₄₀P₁₄B₆. While the as-received sample has T_c=510K, thermal cycling to 700K yields a two-phase system, one of the phases have a broad transition around 425K. Annealing for three hours at 800K causes this transition to sharpen up, and a second transition at 730K is also observed. The extraordinary Hall coefficient (R₁) has been analysed and is described in terms of linear contributions from each phase. From simultaneous measurements of the ohmic resistivity rho on the same sample it is found that, for the two-phase material, R₁ is related to rho as R₁=a rho +b rho ² for 100<T<300K. In the amorphous state there is an anomaly in rho at T_c. From the relationship between R₁(T) and rho (T) it is concluded that in both amorphous and crystallised materials the side jump is of the same order of magnitude as in dilute Fe alloys.

Electrical and optical properties of CoP alloys are investigated as a function of concentration and of annealing temperature. The sample are thin semitransparent films deposited by vacuum evaporation, which are amorphous at room temperature. Interesting modifications of the optical absorption spectrum in the energy range 0.5 to 6 eV are observed, in particular the disappearance in amorphous CoP alloys of the main peak of pure Co at 0.9 eV, which should provide information on the respective positions of the Fermi level and the different electronic states in the vicinity of E_F. Annealing effects are studied on the electrical resistivity and the optical absorption.

An analytical expression for the transverse susceptibility of an ordered alloy described by a tight-binding Hartree-Fock bandstructure is derived. The intra-atomic electron-electron interactions are taken into account. An exact expression for the spin wave stiffness constant is obtained which takes into account the deformations of the bands of both spin directions in the ferromagnetic structure. A simplified multi-orbital model is thoroughly examined and the computation of the FeRh ordered alloy spin wave stiffness constant is reported.

The authors have studied the inter-related magnetic and transport properties of several amorphous Ni₃RE alloys prepared by sputtering. The resistivity and magnetoresistance measurements reveal new aspects of the influence of the amorphous structure on the transport properties: in particular an increase of resistivity on magnetic ordering and an associated positive magnetoresistance. They analyse the magnetic and transport properties in the random anisotropy model and evaluate the crystal field acting on the rare earth moments.

Electron spin resonance measurements are reported for the (Gd, Y)Ir₂ pseudobinary series. The results indicate that the ESR bottleneck of gadolinium can be broken by dilution with yttrium. The parameters relating to the relaxation rates have been determined by fitting the data to Hasegawa's theory (1959). The results are shown to be consistent with the behaviour of other gadolinium-transition metal compounds.

The Mossbauer effect, which is able to distinguish between isolated and clustered iron atoms, has been used to monitor the long term ( approximately 10⁸s) effects of aging CuFe alloys at room temperature. The results are consistent with the movement of iron atoms by a vacancy mechanism of temperature independent (300-1350K) activation energy Q_c=1.0 eV. The development of nonequilibrium gamma Fe has been monitored by tracing the dynamic changes which occurred over approximately 10⁵s in spectra obtained directly on a 0.89% Fe specimen aged at 400 degrees C.

The valence band densities of states of selected HgCd alloys have been studied using 40.81 eV HeII photoelectron spectroscopy. The binding energies, splittings and widths of the Hg 5d_{5/2, 3/2} and Cd 4d_{5/2, 3/2} peaks have been studied for various alloy concentrations and are discussed in conjunction with previous work on AuCd and AgCd alloys and with the results of self-consistent bandstructure calculations. It has been found that the increase in full width at half maximum of the valence d bands with increasing concentration varies approximately as Z/R², where Z is the like-atom coordination number and R is the like-atom nearest-neighbour distance.