Table of contents

In connection with Pokorny's (1982) recent findings in favour of a defect assembly in metallic potassium consisting of both vacancies and interstitials it is emphasised that: (i) differences of only a few hundredths of an eV between vacancy and interstitial formation energies are compatible with a relaxation model in nearly free electron alkalis; (ii) the presence of interstitials in Na is quite consistent with the defect concentration measurements of Feder and Charbnau (1966).

A first-principles calculation of phonon dispersion curves has been made using the resonant model potential by incorporating relativistic effects. The numerical results for gold show that including the relativistic correction lowers the phonon frequencies by 10% in general.

The extension of the effective medium approximation made by the authors to treat the transport properties of structurally disordered systems is applied to study numerically the DC conductivity of a model liquid metal with a tight-binding single s band of Gaussian atomic orbitals. The non-orthogonality of orbitals is fully taken into account and shown to have appreciable effects. The vertex corrections, which have often been neglected in previous theories, turned out to play very important roles for determining the quantitative as well as qualitative behaviour of the conductivity for the cases of fairly high packing fractions corresponding to ordinary liquid metal densities.

Appearance potential spectra of iron, chromium and phosphorus in the metallic glass Fe₇₄Cr₆P₁₀C₇Si₃ have been measured, and are found to be different from spectra from pure iron and chromium and two stainless steel samples (84/16 FeCr and 74/17/9). The spectra in the metallic glass do not show the slightest change in shape upon crystallisation, and the differences between these spectra and those from the stainless steel samples are therefore attributed to the influence of the metalloids on the band structure.

Experiments on several Y-Co samples near the 4:3 composition show an onset to ferromagnetic order below 10K after an appropriate heat treatment of the samples. The ferromagnetic order is strongly suppressed with the application of hydrostatic pressures of a few kilobars. The results suggest a sensitive preparation dependence of the samples for superconductivity. The superconducting transition temperature as derived from AC susceptibility measurements, has a positive pressure dependence of 0.10+or-0.01 K kbar^-1.

Using the Mossbauer effect the authors have studied the influence of the time and temperature of annealing on the formation of the sigma phase in the Fe-45.5 at.% Cr alloy. They have shown that the formation depends on the two parameters and occurs most rapidly at 700 degrees C, where as 15 minutes of annealing the whole sample exhibits the sigma phase.

A self-consistent set of wavelengths for the M zeta lines (M_IV,V-N_II,III) of 38 Sr-45 Rh (excluding 44 Ru) from pure metal targets is presented along with wavelengths for the N xi (N_IV,V-O_II,III) line of Ba metal and for the K alpha line from C in graphite. The data confirm and extent the measurements of Dannhauser and Wiech.

Rhodium-based metallic glasses have been produced with over 40 at.% metalloids (Si and B). X-ray diffraction studies are presented here on Rh_0.92-xB_xSi_0.08 metallic glasses, with x=0.22, 0.27 and 0.32, as well as mechanical, electrical and thermal analysis data. The structural studies suggest that this system undergoes a considerable change in short-range order with increasing boron concentration.

The local hydrogen vibrations are measured by inelastic neutron scattering techniques in the FeTiH_x system for x=0.06 ( alpha phase), 0.94 ( beta ₁ phase), 1.4 ( beta ₂ phase) and 1.86 ( gamma phase) as well as a function of temperature in the gamma phase. The spectra exhibit both sharp and broad peaks in the energy range of 60-110 meV and are strongly dependent upon H concentration and temperature.

The electrical resistivity, Hall coefficient and thermoelectric power have been measured over a wide temperature range for six amorphous Mg-Zn alloys with compositions between 22.5 and 35 at.% Zn. The electrical resistivity shows a very shallow minimum at about 10K and then increases as T² up to about 30K. A small and broad maximum is observed at a temperature T_max ranging from 30 to 50K. Subsequently, the resistivity decreases as -(T-T_max)³2/. This newly found temperature dependence continues up to a temperature T₂, above which more or less linear temperature dependence is seen with negative TCR. All the features described above are composition dependent. The Hall coefficient is negative and temperature independent. The data are employed to determine the critical parameters 2k_F/K_p. The value of TCR is found to be always negative, while the ratio 2k_F/K_p is situated around 1.1. The thermoelectric power is negative and shows a non-linear behaviour with temperature below about 200K.

A theory for the entropy of mixing of compound-forming liquid binary alloys, in which the formation of two types of compound is assumed, is proposed on the basis of the hard-sphere model and applied to the liquid Na-Sn alloy. The theoretical results are in good agreement with the experimental results for the liquid Na-Sn alloy reported recently by Tamaki et al. (1981) who found experimentally that two types of compound, NaSn and Na₃Sn, are formed in the liquid Na-Sn alloy.

The alpha - alpha ' phase transition of hydrogen in Pd_0.9Ag_0.1 and Pd_0.8Ag_0.2 has been investigated by X-ray scattering. The sample contained a constant, average hydrogen concentration, close to the critical concentration. However, a critical point could not be observed, and the alpha and alpha ' phases coexisted up to T>T_c, where T_c is taken from solubility measurements. This effect is discussed in terms of internal stress fields, originating from hydrogen exchange between the two phases, which are embedded in an elastically responding host lattice. The internal stresses prevent the phases from merging into one homogeneous phase above T_c; they have been determined to be of the order of 10⁸ N m^-2. In an accompanying study the lattice parameter change of Pd_0.9Ag_0.1 per% hydrogen concentration has been determined to be (6.6+or-0.2)*10^-4.

A density functional pseudopotential formalism is used to calculate the heat of formation and the volume of formation of disordered solid alloys formed by two alkali metals and two alkali-earth metals. The results are then analysed in terms of the semi-empirical parameters (electronegativity, charge transfer and interstitial electron density) often used in the semi-empirical descriptions of the alloy formation process.

Electronic energy bands of transition metal dihydrides VH₂ and NbH₂ have been calculated by the composition wave variational version of the APW method. The crystal potentials have been constructed by the superposition of the atomic potential of Herman and Skillman (1963). The band structures thus obtained have been utilised to calculate the density of states, optical absorption spectra and Fermi surfaces of these two transition metal hydrides. The results of VH₂ have been compared with the theoretical work of Kulikov (1979).

The transverse magnetoresistance at liquid helium temperatures and in magnetic fields up to 13 T is reported for one single crystal each of Gd, Y and Pr with residual resistivity ratios of 500, 226 and 165 respectively. All the open orbits suggested by the results can be found on the APW or RAPW models of the Fermi surfaces although not all the aperiodic open orbits predicted for Y and Pr were observed. The field dependence of the resistance of Pr suggests that some of the magnetoresistance is due to a reduction of Fermi surface area as the magnetic moment develops with applied field.

The electric field gradient q and asymmetry parameter eta are calculated for non-magnetic dilute copper alloys. Both the valence and size-effect contributions are evaluated explicitly. The transition metal model potential theory is used to evaluate the contribution from the valence effect. The formalism due to Sagalyn and Alexander (1977) is adopted to evaluate the size-effect contribution. Only the size-effect parameter lambda is introduced to explain q and eta , whose calculated values are found to be in close agreement with the experimental values. The effective hardness of fourth row impurities is found to be larger than that of the fifth row impurities. The magnitudes of q and eta are found to be proportional to the effective charges on impurities if the evaluation of these charges includes both the size effect and bound state.

The electrical resistivity rho and the thermoelectric power Q of liquid mercury-based binary alloys containing Tl and Cs respectively have been measured. For Hg-Cs alloys, strong minima in the curve of Q and its temperature derivative delta Q/ delta T are found at about 5 at.% Cs concentration. At this concentration, the temperature derivative of the electrical resistivity, delta rho / delta T, also shows a maximum. Similar phenomena are found for liquid Hg-Tl alloys though its tendency is a little weaker. These facts and the recent data of the thermal expansion coefficient of these alloys measured in the authors' laboratory suggest that the temperature dependence of the structure factor or pair correlation function changes remarkably at 5 at.% Cs or Tl. The authors conclude that the anomalous electronic properties of liquid mercury alloys can be characterised generally by the presence of higher-order correlation effects of atomic configuration, in addition to the simple effects due to pair correlation terms.

It is shown how surface scattering may lead to substantial deviations from Matthiessen's rule. Using an angularly dependent surface scattering parameter as modelled by Soffer (1967), limit expressions for surface scattering in foils and wires are presented for both high and low kappa regions, where kappa is the ratio of the foil thickness, d, or wire radius, a, to the bulk electron mean free path, lambda _infinity . From considerations for general values of kappa it is shown that surface scattering, at temperatures where the residual resistivity dominates, simply enhances the bulk temperature dependence. For higher temperatures for which the bulk resistivity varies as T⁵ the surface scattering can lead to an apparent T² dependence. Further, it is shown that only for very thick samples or high temperatures where kappa >>1 is it possible to use a simplifying expression of the form rho - rho _infinity =³/₈ rho _infinity lambda _infinity /t, for the resistivity of foils or wires, where t is d or a. For most experiments the full theory is necessary to deduce rho _infinity lambda _infinity ; consequently virtually all previous determinations of this parameter are erroneous. Moreover, because of the influence of the surface scattering on the apparent temperature dependence of the resistivity, even of relatively thick material, several of the 'bulk' temperature dependences previously deduced for pure materials are almost certainly in error.

The effects of annealing high-purity polycrystalline gold foils (+99.999%) with thickness d approximately=25 mu m at 870+or-20 degrees C under reduced chlorine pressure p(Cl₂) (in the range 11<or approximately=p(Cl₂)<or approximately=330 Pa) are reported. Detailed size-effect measurements at temperatures over the range 4.2<or=T<or=20K on samples with 2<or approximately=d<or approximately=25 mu m are presented and interpreted according to the theory of Soffer (1967). The results show that the chlorine annealing increases the extrapolated bulk resistivity ratio RRR_infinity of the foil from +or-600 to +70000 for the optimum annealing conditions, where RRR identical to R_273K/R_4.2K. Also a temperature-independent product of the bulk resistivity rho _infinity and the bulk electron mean free path lambda _infinity , rho _infinity lambda _infinity =(9.6+or-0.6)*10^-16 Omega m², is found. With this value of rho _infinity lambda _infinity , the data compare very well with Soffer's theory for a surface roughness parameterr identical to h/ lambda _e approximately=1, where h is the root mean square surface roughness and lambda _e is the Fermi wavelength of the conduction electrons, for freshly annealed samples while r>>1 for surfaces etched in aqua regia. In both cases r is independent of temperature, Kondo-effect measurements reveal the presence of 3.0+or-0.1 at PPM Fe in the as-received Au foils. The decreasing rho _infinity (4.2K) is attributed firstly to the physical removal of the Fe impurities, as previously found by Walker (1970), and secondly to the clustering, passivation and removal of other impurities, probably accompanied by reduced grain-boundary scattering. The results of the Cl₂ annealing are compared with the well-known oxygen annealing method for noble metals, applied on some of the Au foils. It is inferred from this that the former method is much more effective (RRR_infinity being roughly ten times better). Important ageing effects in RRR_infinity at 300K, established in both methods, are reported for the first time and are tentatively correlated to changes in grain-boundary scattering with time.

The existence of induced surface states in the 110 gap of a 110 alkali metal surface is investigated using a simple two-step model for the surface potential. The adsorbate is characterised by two parameters, the height E₁ and width A of the intermediate step. Those values of E₁ and A are determined for which localised surface states exist. The influence of transitions between occupied bulk states and empty surface states is studied by means of the effective dielectric function epsilon ^eff and the differential reflectance Delta R/R⁰. The calculated surface contribution to epsilon ^eff for all parameter sets agrees qualitatively with the experimental curves. The magnitude of the surface contribution depends sensitively on the parameters of the surface potential. This work suggests that the Mayer-El Naby anomaly (1963) in the alkali metal spectra originates in an induced surface state.

The spin-fluctuation theory of Hasegawa (1979-1981) is applied to the paramagnetic state of gamma -Mn, Cr and V, using the densities of states derived from accurate band calculations. The temperature dependence of the calculated susceptibility is qualitatively correct in each case and the temperature dependence of the root-mean-square atomic spin is also calculated. The results are discussed in relation to previous theoretical work and to some of the results of neutron scattering and photoemission experiments.

For pt.I see ibid., vol.11, p.1669 (1981). The hyperfine field (H_T) of Ga, As, Nb, Ru and Ir in Fe has been measured as a function of pressure to 15 kbar at room temperature and that of V in Fe and Mn in Fe and Ni to 7 kbar at 77K. The value of ( delta lnH_T/ delta P)_T for Mn in Fe at 77K is only one half that at room temperature. Apart from FeMn the temperature dependence of the HFF of all the above impurities, and of Pt in Ni and Ir in Fe, is identical to that of the host magnetisation in the low-temperature limit in agreement with spin-wave theory. Above the low-temperature limit the impurity HFF at constant volume is a stronger function of temperature than the host HFF for all the Fe alloys but a weaker function for NiPt.

The authors present NMR measurements on those compounds which are known to pass from ferromagnetic to antiferromagnetic order as a function of the Sn to In ratio-a 'bond randomness' transition. They find evidence for a two-phase region in the magnetic phase diagram, in which ferromagnetic and antiferromagnetic domains coexist, and a concentration region in which an antiferromagnetic and a spin-glass phase coexist.

A singlet-singlet model for induced magnetism in amorphous systems is developed by assuming that the energy splitting Delta varies randomly over the rare-earth sites according to a Gaussian distribution. The exchange interaction is represented by the Heisenberg Hamiltonian. The authors first calculate the susceptibility as a function of temperature in the dilute regime (no ordering) for different values of the relative width of the Gaussian. Induced ordering is treated in a random effective field approximation. In the ferromagnetic case, they calculate the spontaneous magnetisation and the ordering temperature as functions of the relative exchange strength. In the antiferromagnetic case, the ordering is assumed to be spin-glass like and they calculate the 'order parameter' as well as the ordering temperature. Finally, they present the specific heat as a function of temperature in both dilute and ordered regimes. The results are in good agreement with experimental data on the amorphous alloys Pr_xLa_80-xAu₂₀ which apparently correspond to the antiferromagnetic case.

The isomer shift observed by means of ¹⁵⁵Gd Mossbauer spectroscopy in intermetallic compounds composed of Gd and one of the metals M=Al, In, Pb, Sn, Zn, Cu, Ni, Co, Fe or Mn was analysed in terms of a model proposed earlier for the ¹⁹⁷Au isomer shift in Au based materials by Miedema and van der Woude (1980). In combining Gd with s, p metals (Al, In, Zn, Pb, Sn) the s electron character at the Gd sites is decreased while the d electron character is increased. Upon compounding Gd with Cu or 3d metals, both the s and d electron characters are decreased. In the cubic C15 type compounds RM₂, the decrease of the d character is strong in particular when M is Ni, Co or Fe. For most of the compounds investigated the ¹⁵⁵Gd hyperfine fields were also determined.

Mossbauer spectroscopy measurements were made at the Fe sites in the pseudo-binary compounds (Zr_1-xHf_x)Fe₂. The experimental results indicate the existence of two kinds of site with respect to isomer shift and quadrupolar interaction behaviour. An explanation based on a tight-binding model and taking into account the existence of a magnetisation axis along the (111) direction is presented for the observed hyperfine electric interactions.

The authors present the results of high resolution measurements of bremsstrahlung excited Auger electron spectra in the 5d series. The spectra provide an experimental test of atomic models. The measured effective Coulomb interaction between the final state holes displays a jump in value between Pt and Au, analogous to that between Ni and Cu in the 3d series. This similarity supports the validity of a quasi-atomic model of screening for the 5d metals.

The X-ray induced photoemission from clean pure plutonium metal is described and the results for both core and valence levels are compared with previous measurements on light actinides. It is found that, as in thorium and uranium, the configuration interaction plays an important role for core levels, in particular for those of the n=5 shell. The experimental valence-band spectrum confirms the existence of 5f states at the Fermi level and is compared with a density of states of FCC Pu derived from a recent relativistic band structure calculation.