Table of contents

Neutron scattering experiments reveal an exceptionally large temperature dependence of specific phonon branches in CeAl₂. In particular, this behaviour is observed in the lowest optic branches starting from the Gamma '₂₅ phonon and in the TA (100) branch. There is strong evidence that these effects are caused by the interaction between optic phonons and the crystal electric field excitation Gamma ₇ to Gamma ₈.

A new relationship for the melting point, the boiling point and the critical point of metallic elements is derived.

Based on a simple tight-binding model taking only p states at the As sites and d states at the metal sites into account, the structural trend of 3d transition-metal monoarsenides, as found by experiment, can be described in terms of band energies obtained from local densities of states. The result confirms the validity of the model utilising itinerant d states which hybridise with As p states even for the strongly ferromagnetic compound MnAs.

Discrepancies between two recent density functional calculations of the ground-state energy and work function of a Be monolayer are shown to result from different choices of model local density functionals.

The coefficient S characterising the time dependence of the magnetisation of a magnetic material is calculated in terms of the irreversible susceptibility chi _irr are discussed in relation to experiment and computations. The Barbier plot of H_f against the coercive force H_c is shown to agree quantitatively with theoretical models of H_c. Correlation effects are discussed on the same basis as occurs in interpretations of the Vogel-Fulcher law of spin glasses.

Perturbed angular correlation spectroscopy was used to determine the magnetic hyperfine field at Cd impurities in PdFe alloys of nominal concentration 0.5, 1.5 and 3.5 at.% Fe. The mean hyperfine field follows the bulk magnetisation and shows a broad distribution with a minimum at 1.5 at.% Fe.

The high strength of the nickel-based high-temperature alloys such as Nimonic PE16 depends on the presence of the gamma ', Ni₃(Ti, Al), particles. Results are presented on the size and volume fraction of these particles as determined both by transmission electron microscopy (TEM) and by small-angle neutron scattering (SANS). Both techniques show good agreement with samples solution treated and aged at 700 degrees C. After 16 h the mean diameter is around 10 nm and grows roughly as the cube root of the aging time up to 10000 h at 700 degrees C. The corresponding volume fraction is of the order of 9%.

It has been proposed in a recent paper in this journal (by Frahm and Pfalzgra 1983) that the depth of the first minimum in the RDF of amorphous metals is a good indication of directional bonding. It is suggested here that one of the starting points upon which this proposal is based is comprised because of a failure to take into account resolution effects in the RDF. The proposal and our current state of understanding of the structures of amorphous metals and their simulation are examined.

The Dagens-Rasolt-Taylor, first-principles pair potentials (1975) are used to generate the diffuse-scattered intensity from a Li-10 at.% Mg alloy by means of the Tahir-Kheli intermediate-temperature formulation (1969) of short-range order in binary alloys. When the intensity is subsequently used to extract the pair ordering potential by means of the high-temperature approximation of Clapp and Moss (1966), it is found that the potential so obtained bears little resemblance to that generating the intensity. The difference between them is of the order of 40% at the first nearest-neighbour position, even as far away from the critical temperature as T/T_c>1.6. The Clapp and Moss approximation appears to distort the potential in a selective way for non-equiatomic alloys, depending upon whether the alloy presents short-range order of the 'ordering' or 'clustering' type.

Electrical resistance measurements were used to follow the change in short-range order of type-316 austenitic stainless steel. During irradiation at 713K by ⁶⁰Co gamma rays the rate of ordering increased due to the point defects introduced by the irradiation. However, when the point-defect concentration reached steady state the ordering rate was less than the ordering rate without irradiation. These observations are explained by a model in which vacancies diffuse faster than interstitials and diffusion of interstitials causes the state of local order to change away from its equilibrium value. Model calculations based on the standard chemical rate equations for vacancies and interstitials indicate that the vacancy diffuses about eight times faster than the interstitial at 713K.

The shear modulus G and Young's modulus E of electrodeposited amorphous Co-P and Fe-P tubes and the corresponding ultrasonic attenuation were measured between 0.1 and 10 MHz by a resonance technique. The accuracy was sufficient to evaluate the bulk modulus K and the Poisson ratio nu from G and E. The effect of structural relaxation on the elastic constants was investigated during continuous heating and several isothermal annealing programs. The quantitative analysis of the results is restrained because of the superposition of reversible and irreversible relaxation processes and because of the nearly unknown pre-annealing effects during the heating periods before isothermal treatment starts. But it is possible to derive some ideas concerning short-range order and structural relaxation from the different behaviour of the elastic moduli and the attenuation as functions of time. Relaxation is described mainly by a homogenisation of the material with respect to excess free volume. There are striking differences between the properties of the two alloy systems, particularly in the effects of structural relaxation on their elastic moduli and on their attenuation of sound, pointing to different short-range orders.

A semiempirical model, based on the simple theory of the hard-sphere system, is proposed to determine the entropy of mixing of liquid-metal alloys. The method leads to fairly accurate results for simple as well as compound-forming alloys. Numerical applications are made to NaHg and SbZn alloys.

In this paper the authors apply model tight-binding calculations to the electronic structure of systems in which there are essentially two covalent interactions: the intracluster interaction U and the intercluster interaction V. The atomic structure is simulated by a modified Bethe lattice which incorporates closed loops as a possibility. The ratio alpha =V/U is an important parameter to be varied. At a distinct value, alpha _crit, a metal-non-metal transition takes place. The results are applied to the electronic structure and chemical stability of anion cluster in liquid and solid alkali-group-IV alloys. The physical parameters which govern the process of clustering are discussed.

For pt.I see ibid., vol.11, p.1605 (1981). Based on the general formulation in the effective-medium approximation for transport properties of liquid non-simple metals proposed previously by the authors, a numerical calculation of the DC conductivity is made for a model liquid metal with a tight-binding single s band. It is found that quite large contributions to the conductivity are obtained for the dense packing case from the so called vertex corrections, which have often been neglected in previous studies. The interesting behaviour of the corrections is shown to be understood in terms of their structure factor in a comprehensive manner. The effects of non-orthogonality are also studied. Fairly general conclusions about the transport process in the tight-binding band can be derived from the numerical results.

The authors have measured the electrical resistivities rho , of the light rare-earth metals, Pr, Nd and Sm from room temperature to above their melting points. They find, for the liquid phases at their various melting points, that the values of rho _L are 139+or-2, 154+or-2 and 182+or-2 mu Omega cm for Pr, Nd and Sm, respectively. Similarly, d rho _L/dT values are measured to be 0.035+or-0.0003, 0.023+or-0.002 and 0.052+or-0.004 mu Omega cm degrees C^-1, again for Pr, Nd and Sm respectively. These results as well as measurements of rho (T) in the solid phases are discussed in the context of recent theoretical work.

Precise measurements of the temperature dependence of the Hall effect are reported for the amorphous alloys Pd₃₀Zr₇₀, Ni₆₄Zr₃₆, Ni₂₄Zr₇₆, Fe₂₄Zr₇₆ and Cu₅₀Ti₅₀ as well as Pd₈₀Si₂₀ in the temperature range from 15 to 300K. In all cases the Hall resistivity was found to depend linearly on the magnetic field, which was varied from 0.1 to 1.2 T. The absolute value of the Hall coefficient decreases with increasing temperature in the transition-metal-transition-metal alloys. Some possible explanations are discussed.

Measurements are presented of the thermoelectric function of dilute Mo-Nb, W-Ta and Ta-W alloys in the temperature range 2-7K. The experiments on alloys from the middle of the transition series were undertaken to compare and contrast the results with those obtained from alloys based on Pd and Pt for which the d band is almost full. The data are separated into diffusion and phonon-drag components and are compared with simple theoretical models. Rather surprisingly the results correspond more closely to a simple s-d model than to a calculation based on first principles, although the delicate balance of contributions from different parts of the Fermi surface makes the lattice approach in these metals extremely difficult.

The d spectral electron distribution is reported for 2-3 nm nickel particles vacuum deposited and embedded in MgF₂. The study is performed by soft X-ray emission (XES) and absorption (XAS) spectroscopies. Results are discussed in comparison with previous ones obtained for nickel embedded in aluminium. Two kinds of modification are observed: first, those which are independent of the matrix and are ascribed to a partal localisation of the occupied d states due to the size decrease and to the loss of long-range order, and, second, those which depend on the existence of an overlap between the orbitals of the nickel particles and the embedding matrix. When such an overlap occurs, as in the case of an aluminium matrix, the localisation of the empty nickel d states is not observed; such a localisation is observed for the MgF₂ insulating matrix.

Transverse electron focusing (TEF) of electron-like and hole-like orbits has been observed in zinc single crystals and used to investigate the probability (p) of specular reflection of conduction electrons at sample surfaces. The measured value of p ranges from 0.0+or-0.1 to 0.61+or-0.02 depending on both crystallographic planes and kinds of orbit. For the third-zone lens-orbit signals, the amplitude ratio between the two different geometries and the angular dependence of the focusing field are analysed on the basis of a simple geometric model of electron focusing (GMEF). The effect of surface treatment has also been tested.

It was shown recently that transition-metal (TM) compounds with the TM component from the second long period show higher T_c than the analogous compounds having TM components from the first and third periods. The rule is held provided the TM components have four to seven outer electrons. In the present paper it is shown that the same rule can be applied to compounds with TM components having three outer electrons, but cannot be applied to compounds with TM components having eight and nine outer electrons.

The theory for an array of Josephson coupled superconductors is formulated in terms of temperature-ordered Feynman diagrams. The individual grains have an unperturbed ground state with a fixed number of electrons rather than a fixed phase. The formulation is illustrated by calculating the free energy. With relevant approximations this justifies the frequently used planar rotator model and the Giovannini-Weiss form for the free energy.

Using the model of Doniach and Engelsberg (1966) for paramagnon-induced electron-electron interaction the author calculates mass enhancement parameter lambda attributed to this interaction. The paramagnon propagator is calculated in the random phase approximation and a subset of vertex diagrams is summed. He shows that the mass enhancement is already well approximated by the first term in this series. In the almost ferromagnetic region the dynamical coupling strength lambda ( omega ), however, is strongly affected by higher-order contributions in the high-energy region.

The electronic structures of itinerant de electrons in the intermetallic compounds YMn₂, YFe₂, YCo₂ and YNi₂ with cubic Laves-phase structure are calculated using both the recursion method and the standard method of the tight-binding approximation (TBA). Using the calculated density-of-states curves in the TBA and taking the effect of spin fluctuations into account, the temperature dependences of the paramagnetic spin susceptibility in these compounds are calculated. The field dependence of the induced magnetic moment in YCo₂ at OK is also calculated. Good agreement between the calculated and observed results can be obtained by allowing the number of d electrons to be an adjustable parameter. Furthermore, the densities of states for magnetised YCo₂ and ferromagnetic YFe₂ are calculated. It is shown that the values of the local magnetic moments on Co and Fe are smaller than those in pure metals and the local magnetic moments on Y become negative due to the hybridisation between the d bands of Y and Co or Fe.

Cubic NaZn₁₃-type compounds of the form La(Fe_xAl_1-x)₁₃ was stabilised with compositions between LaFe₆Al₇. For compositions above LaFe_11.2Al_1.8 (x=0.861) a low-temperature antiferromagnetic state is present in small external fields. However, upon increasing the field to a few tesla, an exceedingly sharp spin-flip transition with remarkably large hysteresis occurs to the fully saturated ferromagnetic state. The origins of this unusual metamagnetic transition are discussed in terms of the special crystal structure.

The conduction-electron spin resonance linewidths of polycrystalline foils of five dilute alloys of aluminium have been measured in reflection at 9.27 and 20.9 GHz. From these linewidths, spin scattering cross sections are obtained for copper, iron, silver, magnesium and zinc in aluminium. Although not conclusive, the evidence suggests that for low levels of impurities the linewidth contributions attributable to these impurities are independent of frequency.

First measurements of the solubility of tritium in bulk palladium are reported in the pressure range of 0.016<or=p<or=1.33 bar, temperature range 60<or=T<or=400 degrees C and concentration range 0.0015<or=x<or=0.020 (for x in PdT_x). The solubility of tritium at low concentrations of PdT_x follows the trend of the isotropic effect of the solubility observed for PdH_x and PdD_x. In addition, the partial molar enthalpies Delta H(T₂)^infinity and non-configurational entropies Delta S(T₂)^{infinity ,nc} show a significant temperature dependence in agreement with previous work on the PdH_x and PdD_x systems.

NiTi alloys with different transition temperature sets M_s, T_R and A_f are considered here to be affected by cycling between the martensite and the parent phase. In alloys with a starting temperature M_s higher than 50 degrees C, M_s can shift on cycling below the critical temperature T_R at which a transition to the rhombohedral (R) phase appears. Alloys with M_s<<T_R do not suffer this shift of M_s on thermal cycling. Cycling strengthens all the alloys examined. Processing factors can modify both the initial transformation temperatures and the cycling behaviour.