Table of contents

All the Bernal holes were found in a realistic structural model of amorphous iron generated by a computer. Tetragonal dodecahedron occurred much more frequently in number than archimedian antiprism capped with two half-octahedra.

Based on the previously derived antiferromagnetic coupling between the conduction electrons and the localised moment, a numerical calculation has been performed to show that the localised moment plus its compensation cloud contribute a Curie-Weiss susceptibility chi =C/(T+ theta ) with theta >0. By checking with experiments, it is concluded that the polarisation occurs in the near vicinity of the localised moment.

Electron diffraction work has been carried out on yttrium films prepared in a vacuum of 5*10^-7 Torr during evaporation. The crystal structure of thin yttrium films (300 AA thick or less) is mainly face-centred-cubic with a₀=5.25+or-0.05 AA which can be attributed to cubic yttrium dihydride. The amount of the FCC phase decreases with increasing film thickness and films about 600 AA thick are mainly HCP alpha yttrium. When air and hydrogen are admitted to the system, the films react to form oxide and hydride respectively. The time dependence of the electrical resistance of these films has been studied and it is found that in the case of hydrogen contamination there is a minimum in the resistance-time curve. Electron diffraction observations have also been made. All the films transform to Y₂O₃ when heated in an intense electron beam inside the electron microscope. The resistivity results are discussed in terms of the known electrical resistivities of compounds of yttrium.

The elastic diffuse scattering of long-wavelength neutrons ( lambda =4.95 AA) by niobium-oxygen BCC solid-solution alloys NbO_0.026 and NbO_0.036 has been studied in the (001) reciprocal plane for 0.2<4 pi sin theta / lambda <2.25 AA^-1. Broad intensity peaks were found around the (100), (1/200) and (1/21/20) reciprocal lattice points. There was no small-angle scattering. The diffuse scattering due to the distortion of the lattice by random oxygens in octahedral or tetrahedral sites was calculated in the (100) and (110) directions and agreed with the experimental data only in the long-wavelength limit. The observed diffuse intensity peaks were then attributed to short-range ordering of interstitial oxygen. The authors' conclusion is that the clusters inferred by Gibala and Wert (1966) from internal friction data are not random, but correlated up to distances of the order of 20 AA, at least in (001) planes.

The liquid structure factors for four high-temperature states of fluid rubidium are constructed using the Monte Carlo method and the effective pair potential developed by Price (1971). The calculations are compared with the measured structure factors of Block et al. (1977 Liquid Metals 1976 Inst. Phys. Conf. Ser., no.30, p.126) and are found to differ significantly in the vicinity of the principal maximum. The prescription used to construct this pair potential does not appear to provide the necessary density dependence. Some details of procedures used to construct the structure factors are included in the discussion.

The results of pulse echo measurements on polycrystalline V-Cr samples with approximately 0, 20, 40, 60, 80 and 100 at.% Cr show that the bulk modulus B and the shear modulus G increase nearly linearly with increasing chromium content between 0 and 80 at.% and between 40 and 100 at.% respectively. Due to the Neel point anomaly, the value of B at 100% Cr is about 20% lower than at 80 at.% Cr. In the range below 40 at.% Cr G rises slowly because of the decrease in the molar volume, but is apparently almost independent of the electron concentration. The estimated anisotropy ratio has a fairly marked minimum at about 40 at.% Cr.

For pt.I see ibid., vol.7, p.1841 (1978). Studies the electronic structure contribution of transition impurities in noble (copper) or transition (first series) metal to the variation of Einstein's frequency and to the excess vibrational entropy. The authors investigate the importance of this phonon contribution and its evolution with the impurity excess charge. The numerical results exhibit the correct order of magnitude and predict systematic variations of these quantities along the transition series. Numerical results are presented and discussed for the vibrational contribution of transition impurities in alpha and gamma iron-based alloys.

When a metallic solid is strained below its elasticity limit, in any locally dilated zone two competitive effects take place: thermoelastic cooling and heating due to internal friction phenomena. During an adiabatic tensile test, a measure of the critical strain rate at which the two effects balance allows for the determination of both the longitudinal viscosity coefficient and the related relaxation time.

Published diffusion data permit an extensive comparison to be made between tracer diffusion coefficients, D, in Pb and in alpha -Zr, at 0.6 T_m, where T_m(K) is the melting temperature of the host metal. For these metals, a striking correlation is found between D and the metallic radius, r, of the corresponding tracer element; except for the smallest r values, the correlation may be expressed in the general form lg D=A+exp(-br+c) where A, b and c are individual constants for each host metal. There is, for tracer diffusion in Pb, sufficient experimental data to permit the evaluation of an additional relationship, of the type proposed by Zener, between the preexponential factor, D₀, and the activation enthalpy, Delta H, in the usual expressions D=D₀exp(- Delta H/RT) describing the temperature dependence of D. A combination of these relationships allows the evaluation of expressions for D₀ and Delta H in which r is the only variable. In order to compare tracer diffusion in these 'open' metals (i.e. metals with a relatively large metallic/ionic radius ratio) with tracer diffusion in a 'full' metal, values of D at 0.6 T_m have been calculated from published data for diffusion in Cu.

Doppler broadening measurements have been performed on Cu samples containing vacancies and/or hydrogen. Trapping of hydrogen by vacancies is indicated above about 150K. Vacancies occupied by hydrogen show a strongly reduced positron-trapping probability as compared to hydrogen-free vacancies. Detrapping of hydrogen is not observed below 450K. Therefore, the vacancy-hydrogen binding energy must be greater than 0.4 eV. The positron measurements also show that quenched-in vacancies become mobile at about 273K and form clusters. The close analogy to the annealing behaviour of electron-irradiated Cu confirms the interpretation of annealing stage III by single-vacancy migration.

It is pointed out that there exists a simple formula for the static electron gas dielectric function, incorporating exchange and correlation effects, which generates calculated physical properties with surprisingly good precision and which has a very good formal justification.

Calculations of the electrical resistivity of molten Ti are presented, using the t matrix approach with muffin-tin potentials obtained by a number of approximations of current physical interest. Results are compared with recent calculations by Hirata (1977) using different approximations.

de Haas-van Alphen effect measurements have been made of the cyclotron effective masses for a large number of orbits over the Fermi surfaces of potassium and rubidium. Problems of measurement that arise in the pure metals from magnetic interaction and finite skin depth effects were avoided by working with dilute alloys of K(Na) and Rb(K). For potassium the authors find m*/m₀=1.230+or-0.013 with no evidence of anisotropy, but for rubidium they observe an anisotropy of 3.1% and a mean value of m*/m₀=1.260+or-0.001. The variation of electron quasiparticle velocity over the Fermi surface has been computed from a cubic harmonic representation of the experimental data. These experimental results lend support to calculations by Leavens and Carbotte (1973) of the anisotropic electron-phonon renormalisation and permit the magnitude of the electron-electron renormalisation in these metals to be estimated.

A tight binding formulation is presented for the electronic transport coefficient such as DC conductivity and the Hall coefficient of structurally disordered systems. The formulation is performed with special care about the consistency with the calculation of the electronic density of states. Among existing theories for the density of states the approximation scheme proposed by Ishida and Yonezawa (see Progr. Theor. Phys., vol.99, p.731 (1973)) is especially considered here. Numerical calculations of the conductivity and the Hall coefficient are performed for a model of one hydrogen-like 1s orbital per atom. The atomic distribution function is assumed to be of a random hard-sphere type. A detailed analysis is made for the change of the transport properties with varying input parameters characteristic of the model, i.e. density and the hard-sphere diameter (in units of the effective Bohr radius). The results are also compared with those obtained from the random phase model due to Mott (1967), Hindley (1970) and Friedman (1971).

The t matrix approach to the problem of electrical resistivity has been used to study the pressure variation of the electrical resistivity in Cu, Ag and Au. The calculated results indicate that the t matrix approach gives reasonable agreement with the pressure dependence of the electrical resistivity of metals considered.

The conditions of internal oxidation of impurities in polycrystalline gold wire of nominal purity 6 N have been studied. The annealing in pure oxygen at normal pressure proved to be more efficient than standardly used annealing in air, while annealing at reduced oxygen pressure has not been successful. This behaviour can be understood as being due to the extremely low solubility of oxygen in gold. The oxidising treatment made it possible to suppress the concentratPPMion of free iron impurities from 2.6+or-0.4 atPPM in the as-received state to well below 0.2 atPPM as determined from the resistivity minimum effect. The impurity oxides are presumably responsible for large deviations of longitudinal magnetoresistance from Kohler's rule, indicating their strong contribution to small-angle electron scattering at low temperatures.

Measurements have been made of the thermopowers of a series of alloys covering the complete alpha phases of Cu, Zn, Ga, Ge and As in Ag. The data for these alloys and for the corresponding Cu-based systems are analysed on a two-band model using supporting data on resistivity and lattice thermal conductivity. The phonon drag component shows enhancement at low solute concentrations and the behaviour of this at about 30-40K is described within the framework of a simple model. The full temperature and concentration dependence of the diffusion component requires further sophistication of the model.

The Hartree-Fock Hubbard Hamiltonian is used to study the generalised spin glass behaviour of transition metal alloys in which the solvent is paramagnetic and the solute ferromagnetic in the bulk but an isolated atom of the solute does not carry a moment. The critical spin glass concentration c_sg and the alloy susceptibility are determined in a simple molecular field and also coherent potential approximations. In both cases the alloy susceptibility exhibits the characteristics cusp at c_sg.

A semiclassical Green's function method is used for studying long-wavelength spin wave excitations in amorphous ferromagnetic alloys with randomly orientated single-ion anisotropy. The dispersion law and the density of states of such excitations are calculated both by a Green's function truncation procedure and numerically using a Monte Carlo technique to generate the ground state of the system. Both procedures yield a gap in the excitation spectrum which increases monotonically with the anisotropy constant and is somewhat smaller than the gap in the related crystalline ferromagnet. In addition, the density of states of the spin wave excitations, as calculated numerically, shows the possible existence of localised states in the gap region.

The effects of a low lying Gamma ₈⁽¹⁾ excited state on the ESR properties of the ground state Gamma ₇ doublet are demonstrated for the rare earth ions Er and Dy in the beryllides LaBe₁₃, LuBe₁₃ and ThBe₁₃. The analysis of the authors' ESR results yields a rough estimate of the Gamma ₇- Gamma ₈⁽¹⁾ splitting. Further, the ESR data, including those of Gd in the same hosts, suggest the near independence of the localised conduction electron coupling on the rare earth 4f occupation number.

The authors have studied transition and noble metal site NMR spectra of stoichiometric, off-stoichiometric and substituted Heusler alloys. The hyperfine fields can be analysed consistently in terms of local and transferred contributions. The transferred fields are negative at near neighbour and second neighbour to a Mn site, and positive at third neighbour. In many cases excess Mn atoms substituted onto Z sites form antiferromagnetic good local moments in these ferromagnetic hosts with strongly anomalous hyperfine field temperature dependences. Both the transferred fields and the Mn-Mn coupling follow the predictions of a Friedel-Anderson d resonance model correctly treated in the preasymptotic region. The local hyperfine fields at Mn sites are very similar to fields in dilute Mn alloys, while the local fields at Co sites are positive indicating unquenched local orbital moments on the Co atoms.

Spin echo NMR measurements on off-stoichiometric Heusler alloy samples show that Al and In have strong positive hyperfine fields when the atoms are on Mn sites. This result is compared with the predictions of hyperfine field models.