Table of contents

An analytic solution of the Percus-Yevick equation for the hard-sphere model is applied to the thermodynamic properties of liquid 3d transition metals near the triple point. Agreement between theory and experiment is fairly good for the specific heat and heat of vaporization.

Hydrogen diffusion was studied by quasielastic neutron scattering in the system alpha -NbH_0.004 with 0.7 at.% nitrogen impurities, for temperatures between 180 and 373K. From comparing the spectra at small and at large scattering vectors, the trapping of the hydrogen in the vicinity of a dissolved nitrogen atom was studied. Typical trapping times are several hundred times larger than the mean rest time of a hydrogen atom on an undisturbed interstitial site.

The Fourier series representation of the Fermi surface of the noble metals given by Halse (1969) is updated taking into account the results of more recent and accurate de Haas-van Alphen experiments (Coleridge and Templeton, 1972).

The optical absorption spectra in 2-butanol have been studied. The position of the absorption peak which is attributed to surface plasmons of small alloy particles depends on the composition of the alloy. The spectra obtained are qualitatively in agreement with those calculated by Mie's equation.

The temperature dependence of the amplitudes of three tilted field orbits on the Fermi surface of copper has been measured. The expected linear relationship was observed in plots of lnA against T³, and values of the average collision frequency for each orbit have been determined from the corresponding slopes. These have been compared with calculated values using an analytic expression derived from the parallel field RFSE data of Gantmakher and Gasparov. The results as determined by the two methods differ by about a factor of three. The discrepancy results from the differences in the experimentally measured amplitudes.

A theory is proposed for determining d-electron states at transition-metal alloy surfaces. The continued fraction technique is extended to a disordered binary alloy by using the tight-binding approximation. As in the usual coherent potential approximation (CPA) an electronic self-energy is introduced to describe the atomic disorder scattering. It is shown how to determine the d-electron density of states by using the recursion method due to Haydock and others.

It is shown, using a simple variational argument, in the case where a metal is represented by a finite barrier potential, that the surface ferromagnetic instability which exists in the case of an infinite barrier potential model, may disappear for small enough values of the barrier height.

The measured AC susceptibility of PdCo alloys with 3 to 7.5 at.% Co at 5 kHz in applied fields of 0-250 Oe is typical of a bulk ferromagnet near its ordering temperature. The principal maximum in the susceptibility shifts to lower temperatures relative to the zero field maximum as the applied field is increased. Concurrently a second, narrower peak appears which has a small upward shift in temperature, and is identified as the true critical susceptibility maximum.

The satellite structure observed in the XPS spectra of metallic Ni is identified with the separation in energy between 'one-hole' and 'two-hole' final states. Similar structure is observed in Co and can be associated with the Ni and Co levels in Ni₃Fe and CoFe alloys. No such effects are resolved in Fe. The experimental data is discussed in terms of recent many-body theories.

In the first approach considered the vacancy is represented by a spherical hole in an otherwise uniform positive background of charge. The electron density and resulting formation energy, for this jellium model, have been calculated in a non-linear (Kohn-Sham) theory by Nieminen et al. The second approach, originally advocated by Harrison, is based on pseudopotentials and linear screening theory. A third method designated semi-linear theory, which combines features of both the former schemes has recently been proposed by M.W. Finnis. For Na the Harrison model has some relevance and the semi-linear screening approach gives a good estimate of the formation energy. For a high electron density metal like Al, jellium calculations predict unphysical values for the formation energy. None of the existing approaches is adequate for describing the vacancy formation energy of a dense polyvalent metal.

10 MeV electrons were used from room temperature up to 1000 degrees C. In addition the recovery was monitored by resistivity measurements and transmission electron microscope observations. There is strong evidence that the stage III annealing (150- degrees C-350 degrees C) is a result of vacancy migration leading to the formation of voids which coarsen at the higher temperatures. The presence of voids was confirmed by transmission electron microscopy on material annealed to 900 degrees C. The information obtained was the result of a very careful data analysis which is described in some detail, especially regarding angular correlation curves. It shows that the often used one-parameter analysis may be misleading. The positron lifetime and angular correlation results compared in the framework of the 'trapping model' show very good agreement.

The energy bands both in SC and FCC structures are calculated using the relativistic KKR method. In contrast to earlier calculations the results are sensitive to changes in the structure. A nondirect transition model is constructed to explain the optical properties of expanded fluid mercury on the basis of a quasicrystalline model. Discrepancies between optical and electrical transport data are critically examined.

The resistivities at constant volume and constant pressure and the volume derivative ( delta ln rho / delta lnV) were calculated over a range of temperatures (20K to melting) employing a fundamental calculation of the form factor and phonon spectrum. No parameters were adjusted to fit experimental data yet the agreement obtained with experiment was very good. The phonon frequencies were calculated using the recently-developed model potentials of Dagens et al. (1975) and the Geldart and Taylor (1970) screening. The form factors were calculated using the same model potential and screening but also incorporating the non-local electron-electron vertex correction of Rasolt (1975).

In previous de Haas-van Alphen measurements of the electron lifetime in silver alloys, the s-phase shift was thought to dominate the scattering in AgAu while the p-phase shift was thought to dominate the scattering in AgSn, AgCd, and AgGe. In the present work, alloys of AgPd, AgY, AgGd, AgMn and AgFe have been investigated since in these the d-phase shift could be dominant. Values of the s, p and d phase shifts and details of the scattering anisotropy have been deduced for all these silver alloys.

The resistivity was measured with a high relative accuracy ( approximately 10^-3%) in order to determine the temperature derivative of resistivity and its dependence on temperature. Contrary to previous results, the temperature derivative of resistivity was found to be a nonlinear function of a complex character. The most striking feature of this function is a maximum at about 90 degrees C. Towards higher temperatures the temperature derivative decreases exponentially, in the manner similar to that found by the present authors for liquid Pb and Sn. The behaviour of the temperature derivative is compared with that of other physical quantities and a possible explanation suggested.

The local densities of states on (110) and (100) facets of Mo and W are studied in the tight-binding approximation, including the spin-orbit coupling term, and using the moment method and the continued fraction technique. Surface states are found on the (100) plane in agreement with experiments. They are shown not to be produced especially by spin-orbit coupling.

Surface dipole barriers for transition metals have been deduced using calculated internal Fermi levels and experimental electron workfunctions. The internal Fermi levels are estimated from a survey of band structure calculations. They have been checked using a theorem which relates the pressure on a solid to the wavefunctions, their derivatives and energies at the Wigner-Seitz cell boundary. This theorem represents a generalization of a relation previously derived using statistical theory, which was used to provide an independent check on internal Fermi levels in simple metals by imposing the equilibrium, zero pressure condition. Reasonable agreement between band structure and pressure cell-boundary estimates for the transition metal internal Fermi level was obtained. The surface dipole barriers range from 0.2-0.44 Ryd (2.5-6 eV). Their large magnitude is a reflection of the large cell boundary electron densities for these metals.

The Hohenberg-Kohn-Sham spin-density-functional (SDF) formalism is applied. A Stoner-like band mode is derived in the SDF formalism. The solutions of the SDF equations are assumed to have Bloch character and perturbation theory is used to show that the energy splitting between spin up and spin down states is approximately wavevector independent and proportional to an energy-dependent Stoner parameter. This result makes it possible to obtain magnetic properties from the paramagnetic density of states and the Stoner parameter alone. Results in the local-spin-density approximation for the Stoner parameters of V, Fe, Co, Ni, Pd, and Pt are presented. The relative stability of the para and ferromagnetic states is found to be correct for all the elements investigated and the total magnetization compares favourably with experiment. Values for the Curie temperature are systematically too high. Experimental estimates of the Stoner parameter are compared with the calculated values and the deviation is at most a few tenths of an eV.

Previous numerical calculations for a model of nickel alloys, employing the coherent potential approximation (CPA) and the random phase approximation (RPA), are extended to iron alloys. It is shown that often the effective scattering potentials are sufficiently weak for a rigid band calculation of the spin wave stiffness constant D to be a good guide to the more elaborate CPA calculations. The case of NiFe alloys is re-examined in the light of a recent calculation by Riedinger and Nauciel-Bloch (ibid., vol.5, p.732 (1975)). It is shown that D is very sensitive to the assumed exchange splitting in pure nickel and that within the RPA reasonable agreement with experiment is obtained only by assuming an unusually large value for this parameter.

The magnetic properties such as Curie temperatures, spontaneous magnetizations, paramagnetic susceptibilities and their pressure derivatives of PdNi alloys with nickel concentrations below 15% have been measured. All these properties (from our measurements as well from previously published measured values for nickel concentrations up to 40%) are well described in a local model of coupling between nickel moments through the palladium matrix. From the concentration dependence of the Curie temperature and its pressure variation the authors derived values for the exchange integral between localized moments and d electrons and for its pressure derivative in agreement with values found in the case of PdFe and PdCo alloys. The paramagnetic susceptibilities follow a Curie-Weiss law. There exist concentration ranges where the spontaneous magnetization as well as its pressure derivative vary proportionally to the concentration.

The concentration dependence of the exchange stiffness constant was investigated over the Fe concentration range 0 to 0.61. The influence of the ordering of Ni₃Fe and NiFe alloys is discussed.

The longitudinal spin relaxation rates of the ⁶⁹Ga and ⁷¹Ga isotopes in a number of liquid binary alloys of Ga have been measured. From the measured relaxation rates the quadrupole part caused by the fluctuations of the electric field gradients due to the atomic motion has been extracted. The quadrupole rate is found to be considerably increased on alloying; the actual increase for a given composition is heavily dependent on the difference in size of the two types of atom of the alloy. The incoming atom causes a rearrangement of the Ga atoms in the neighbourhood of the 'relaxing' nucleus consequently increasing the field gradient there. The measurements support recent theory which predicts the quadrupole interaction to be of short range. However in as far as it can be determined, the variation of the relaxation rate with temperature predicted by the same theory is found to be different from that observed.