Table of contents

A model for the free enthalpy of mixing including association is proposed. It is shown that the entropy of the associates is proportional to the relative volume contraction of the solid intermetallic compound, the proportionality constant being equal to that for the relation between entropy and relative volume expansion on melting of simple metals and noble gases.

A new transport equation is derived for the linear response of many-particle systems to electric fields.

The authors have analysed existing resistivity data on Cu, Ag and Au by looking at the variation of the resistivity as a function of temperature and specimen size. Evidence is found for an additional temperature dependence due to surface effects, particularly in the case of specular scattering. A T² like behaviour induced by the size is observed. The coefficient of T² can amount to (5/d)f Omega cm K^-2 (d is the reduced thickness in cm). Therefore surface scattering should be accounted for if the electron-electron contribution to the resistivity is to be measured correctly.

The low-temperature DC magnetic susceptibility of the amorphous spin glass (La₇₀Gd₃₀)₈₀Au₂₀ is studied as a function of hydrostatic pressure to 11 kbar. The spin-glass freezing temperature T₀ decreases with pressure at the rate delta T₀/ delta P=-14+or-5 mK kbar^-1 which is opposite in sign to the effect observed in classical spin glasses like AgMn, AuFe and CuMn.

Measurements are presented of spin waves observed in the nearly free-electron metals sodium and potassium, utilising a transmission microwave spectrometer operating at 80 GHz. With very pure material and careful sample preparation it has been possible to detect up to fifty distinct spin waves. The samples, studied at 1.4K, have values of omega tau of the order of 150 where omega is the observational frequency and tau is the momentum relaxation time determined from the linewidth and amplitude decay of the spin waves. Consequently the signals approximate very closely to the infinite omega tau limit. This allows a simple comparison of theory with experiment yielding values for B₀, B₁ and B₂, the first three parameters characterising the many-body spin interaction. For sodium B₀=-0.210+or-0.015, B₁=-0.010+or-0.015 and mod B₂ mod <or=0.02 while for potassium B₀=-0.293+or-0.01, B₁=-0.076+or-0.01 and mod B₂ mod <or=0.01.

High-resolution capacitance dilatometric measurements on the a, b and c axes of terbium and dysprosium indicate that, to a resolution of 1*10^-6, the Neel transitions of both methods are second order. This is both in contrast to the prediction of Barak and Walker (1982), and also in contrast to the case of holmium, which has a first-order Neel transition.

The structure of LaNi₅D₆ has been studied by powder neutron diffraction. It is described in space group P31m with the deuterium atoms distributed over one fully and one partly occupied interstitial site. The dynamics of hydrogen in LaNi₅H₆ at temperatures of 293, 390, 440 and 493K have been studied by cold neutron scattering experiments. According to these the H atoms showed a high local mobility on the partly occupied H site. Assuming a simple diffusive behaviour with circular symmetry for this localised part of the motion, relaxation times of the order of 10^-10 s were obtained at 293K. This indicates H atom jumps about 100 times faster than observed for other types of diffusive motion in the structure. The activation energy for the former was rather low, about 75 meV.

The Percus-Yevick phonon method is applied to liquid Fe, Co and Ni for predicting thermal pressure coefficients which are used for analyses of other thermodynamic quantities involved. The results are compatible with those obtained by other methods or experiments.

Short-range ordered (SRO) kinetics of Cu-20 at.% Zn, Cu-25 at.% Zn and Cu-30 at.% Zn have been investigated by measurement of electrical resistivity during isochronal and isothermal annealing. The samples show a growing atomic mobility with increasing Zn content. After a small and sudden temperature change the new equilibrium state of SRO is adjusted by two distinct processes, giving evidence for the heterogeneity of SRO microstructure. The relaxation times of the two processes differ by a factor of six, but reveal the same activation energy: 1.5+or-0.1 eV for Cu-25 at.% Zn and 1.25+or-0.1 eV for Cu-20 at.% Zn and Cu-30 at.% Zn.

A new experimental technique was used for dilatometric measurements of Cu₆₀Zr₄₀ metallic glass samples under applied tensile stress. The measurements were performed on unrelaxed samples at 473K and gave a detailed insight into the low-temperature relaxation processes. The measurements indicate that the length change is a superposition of two competing processes: (i) low-temperature relaxation which is responsible for sample contraction and (ii) creep which leads to sample elongation. Using a special procedure they were able to discover the contribution of each of the above processes. On the basis of these data it was possible to evaluate the coefficient of viscosity as well as to find its dependence on the applied tensile stress.

The diffusion constant of muons in metals at low temperatures is derived from the muon Boltzmann equation under the assumption that electron-muon scattering dominates, and a T^-1 behaviour is obtained. This temperature dependence compares favorably with the experimental result that the diffusion constant is proportional to T^-0.6 for positive muons in aluminium. However, the calculated absolute value of the diffusion constant around 1K is still in severe disagreement with experiment.

The effects of tetragonal and trigonal shear strains on the electronic structure of vanadium are investigated. Energy levels, the Fermi surface and the density of states in vanadium deformed by shear strains are calculated directly by using the tight-binding parameterisation scheme. Based on the calculated results, the effects of the strains on the electronic structure of 3d-group transition metals with BCC structure are discussed in detail. The dependence on the tetragonal strain of the areas of several extremal orbits on the Fermi surface of paramagnetic chromium and vanadium are estimated: the results for chromium are compared with the experimental results of molybdenum and tungsten, and for vanadium a topological change in the Fermi surface due to the strain is predicted. The changes in the band energy due to the tetragonal and trigonal strains are calculated by a new method and the results are shown to agree qualitatively with the trends of the elastic constants C' and C₄₄ in the 3d-group transition-metal alloys with BCC structure.

The authors have studied the electronic structure of paramagnetic Ni_cPt_1-c random substitutional alloys using the relativistic generalisation of the Korringa-Kohn-Rostoker coherent potential approximation (R KKR CPA) and a first-principles but not self-consistent crystal potential. Spectral functions as well as fully and partially averaged densities of states were calculated. They find a complex set of well defined bands and a Fermi surface which changes subtly with concentration. The results agree with the scant photoemission measurements on these alloys and suggest a number of new effects which could be observed in further experiments. However, they are unable to account for the very broad peak in the linear coefficient of the specific heat near the critical concentration for the occurrence of ferromagnetism. They suggest that this peak is due to spin disorder scattering.

The contribution of the contact interaction in the nuclear spin-lattice relaxation rates of HCP transition metals (Sc, Ti, Y, Zr and Tc) is recalculated using a relativistic hyperfine coupling constant expression in place of the conventional non-relativistic Fermi formula. It is shown that the relativistic effects do not cause such a large change in the relaxation rates as was stated in the previous paper (1982). The revised total theoretical rates are shown to be more favourable than the previous ones, except for Tc, in comparison with the experiments.

A rigid muffin-tin potential analysis is proposed for evaluating interatomic forces in metals. Using this theory, interatomic potential energy curves were calculated for Li, K and Rb. Despite the simple set of approximations used, these results are remarkably similar to the corresponding results obtained from pseudopotential theory. The rigid muffin-tin method is clearly useful for calculating interatomic forces in simple metals and should have a much wider application to all metallic systems.

Analyses of the Doppler-broadening energy spectra for positrons annihilating in solid and liquid Ni are reported. Comparisons are made among the momentum distributions of positron-electron pairs annihilating in the essentially defect-free lattice, the vacancy and the liquid state of Ni. An interesting similarity in the distribution of momenta is reported for positrons annihilating in vacancies at high temperatures and those annihilating in liquid Ni.

The temperature dependences of the electrical resistivity ( rho ), thermopower (S), thermal conductivity (K) and temperature derivatives d rho /dT and dS/dT have been measured in single crystals of PrCd, with the electric field and temperature gradient applied along the (110) direction. Three phase transitions have been identified: a structural transition at T_s=125K, where the high-temperature CsCl structure ceases to exist, an antiferromagnetic-paramagnetic transition at T_N=40K and an unknown phase transition at T^*=20K. Particular attention is focused on the details of the structural transition at T_s, namely on the peculiar irreversible behaviour observed there. An analysis is presented to identify and estimate different contributions to the transport coefficients of PrCd. A brief comment is also made on the problem of the lattice stability in CsCl structure intermetallic compounds.

De Haas-van Alphen (DHVA) quantities have been calculated for several impurities (Al, Si, P, Zn, Ge) in dilute copper alloys and compared with experiment. The theory used describes the scattering of Bloch electrons by a cluster consisting of an impurity together with one or more neighbouring shells of host atoms. Two types of potential, either constructed in a standard way or calculated self-consistently, are used and their representation of the electronic structure of both host and alloys is investigated extensively. In particular, the effect of charge transfer is studied. Comparison of measured and calculated Dingle temperatures x_i and cross-sectional area changes delta A_i reveals that these quantities depend on charge transfer in a different way. While charge transfer influences only the neck values of x appreciably, it enhances the delta A_i values considerably and nearly uniformly. The non-selfconsistent potentials reproduce the Cu(Si)and Cu(Al) DHVA properties quite well but yield less good results for the other alloys, clearly because the dynamical screening effects are not accounted for. The self-consistent potential for Cu(P) is good. The results for the other alloys suggest that it is worth while obtaining these potentials for the (at least 13-atomic) impurity cluster as a whole, rather than for the impurity only.

A technique is described for converting the non-equilibrium currents observed at different bias values in a superconducting tunnel junction, formed between superconductors of different energy gaps and subject to a high-energy incident phonon flux, into an energy distribution for the incoming phonons. The effects both of the theoretical approximations made in deriving the numerical results used in the analysis and of the non-ideal characteristics, observed in real tunnel junctions on the accuracy of the technique are discussed. Results from the application of the technique to various broad-band phonon sources are then described. The thin film cupro-nickel heater is found to emit largely in accord with the acoustic mismatch model, whereas the superconducting tin phonon fluorescer shows enhanced emission above the tin gap energy.

Measurements of the temperature dependence of the thermal expansion and elastic constants of polycrystalline Cr and Cr-Co alloys having compositions 0<c<or approximately=6 at.% Co are reported. The observed anomalies in the spontaneous volume magnetostriction depend linearly on T² up to about 0.6 T_N in good agreement with the theory of magnetoelastic behaviour of itinerant electron magnetic systems. Rather large anomalies in the bulk moduli around T_N have been observed but none in the shear moduli. The calculated values of the anomalies in the bulk moduli are about two times larger than those observed at zero temperature. Furthermore, these anomalies are observed to increase with increasing temperature, reaching their highest values near T_N, in contrast to the theoretical prediction that the anomalies should decrease with increasing temperature. In the case of the 6.09 at.% Co sample, which displays a jump-like behaviour in both the bulk modulus and the thermal expansion coefficient, the results are in agreement with a thermodynamic relation based on Walker's theory (1980) for second-order transitions, i.e. Delta beta dT_N/dp= Delta kappa where Delta beta and Delta kappa are the anomalies in the volume thermal expansion coefficient and the compressibility, respectively.

Muon Knight shift measurements are performed in the pseudobinary intermetallic compound LaAg_1-xIn_x (CsCl structure). Negative, temperature-dependent Knight shift values are found. This observation is discussed in terms of a negative transferred hyperfine field between the La 5d states and the muon, whose magnitude varies from -3 kG mu _B^-1 to -10 kG mu _B^-1 for 0<or=x<or=0.3.

The electronic properties of amorphous and sintered Fe₈₀B₂₀ alloys have been studied by electron energy loss and Auger spectroscopy. A correlation has been attempted between data which have appeared recently in the literature on energy loss and X-ray absorption near edge structures. The comparison of Fe-B spectra with those of Fe and Ni allows the authors to discriminate between the effects due to the presence of the metalloid and those due to disorder. A suggestive relationship between the data and the local environment around each Fe site has been found and discussed.