Showing papers in "Journal of Physics F: Metal Physics in 1973"
TL;DR: The use of positron annihilation for determining vacancy formation energies is covered in considerable detail and put into perspective relative to other methods (eg thermal expansion, self diffusion, nuclear magnetic resonance).
Abstract: Reviews the investigation of monovacancies and divacancies in or near thermal equilibrium at high temperatures. The use of positron annihilation for determining vacancy formation energies is covered in considerable detail and put into perspective relative to other methods (eg thermal expansion, self diffusion, nuclear magnetic resonance). The experimental techniques for studying the trapping of positrons at vacancies and the trapping model used for analysing the experimental results are reviewed. A detailed discussion in terms of ion core size valency, and vacancy relaxation is given of the trapping criteria for different metals. It is shown that the experimental results on the existence or nonexistence of positron trapping by vacancies are well accounted for by the theoretical ideas. The formation energies of monovacancies in metals obtained by the positron annihilation techniques are presented and compared with those obtained by other methods.
334 citations
TL;DR: In this article, the theory of diffuse scattering by point defects and by defect clusters is reviewed, and the Huang scattering very near to the Bragg reflection increases in direct proportion to the number of point defects in the cluster.
Abstract: The theory of the diffuse scattering by point defects and by defect clusters is reviewed. For a small concentration of statistically distributed point defects the symmetry of the long ranging part of the displacement field and the strength of the defects can be obtained from scattering measurements close to the reciprocal lattice points (Huang scattering). In addition to the (symmetrical) Huang scattering an asymmetry of the scattering is observed. For defects with sufficiently large displacements, the sign of this asymmetric scattering determines the sign of the displacement field around the defect and its magnitude yields information about the magnitude of the displacements close to the defect. For defect clusters the diffuse scattering is strongly modified. The Huang scattering very near to the Bragg reflection increases in direct proportion to the number of point defects in the cluster. For larger distances q from the Bragg reflection the intensity decreases as 1/q4.
308 citations
TL;DR: In this article, it was shown that the heat of formation of metallic binary alloy systems is predominantly determined by the electronegativity difference, the difference in electronic density at the boundary of the atomic cell and the size difference.
Abstract: Empirical correlations are established, which demonstrate that the heat of formation of metallic binary alloy systems is predominantly determined by the electronegativity difference, the difference in electronic density at the boundary of the atomic cell and the size difference, the third term being absent for compounds. The work function of a metal is recommended as a measure for its electronegativity. The electron density at the cell boundary is shown to be related to the compressibility of the pure metal. The consequences of the energy effects for quantitative descriptions of charge transfer in metallic alloys are discussed extensively.
245 citations
TL;DR: In this paper, the problems of spin density wave and soft phonon mode leading to periodic lattice distortion as a consequence of nesting Fermi surfaces have been investigated and necessary and sufficient criteria for the existence of each kind of instability and for the coexistence of the two kinds have been derived.
Abstract: The problems of spin density wave and of soft phonon mode leading to periodic lattice distortion as a consequence of nesting Fermi surfaces have been investigated. By examining the changes in the energy functional of the electron-lattice system as small amplitude spin density wave and periodic lattice distortion develop, the necessary and sufficient criteria for the existence of each kind of instability and for the coexistence of the two kinds have been derived. These results are expressed in terms of the generalized susceptibility function of the electron system, the Coulomb and exchange interactions between the electrons, the electron-phonon coupling and the phonon frequency.
225 citations
TL;DR: In this article, the results of Mossbauer measurements on dilute Fe-based alloys with all soluble transition impurities are given; the spectra are analyzed to obtain hyperfine field and isomer shift changes at first, second and average further neighbor shells.
Abstract: Results of Mossbauer measurements on dilute Fe based alloys with all soluble transition impurities are given; the spectra are analysed to obtain hyperfine field and isomer shift changes at first, second and average further neighbour shells. The hyperfine field changes are shown to be consistent with a model in which the conduction electron polarization has a linear response to the d moment changes induced by the impurity. The isomer shift changes are ascribed primarily to variations in the d spin up density at the Fe neighbour sites.
215 citations
TL;DR: In this paper, a new approach to the analysis of positron annihilation long slit angular distributions is presented, which provides a more direct measure of the Fermi surface profile, is applied to data for Cu and the results are found to agree well with the computed surfaces of Roaf and Halse.
Abstract: A new approach to the analysis of positron annihilation long slit angular distributions is presented The analysis, which provides a more direct measure of the Fermi surface profile, is applied to data for Cu and the results are found to agree well with the computed surfaces of Roaf and Halse The same analysis provides a guide to the form and intensity of that part of the angular distribution arising from the annihilation of electrons occupying states in the filled Brillouin zones
207 citations
TL;DR: In this paper, the authors reviewed the contribution that transmission electron microscopy has made to the understanding of the mobility and clustering of point defects in fcc and bcc metals.
Abstract: Reviews the contribution that transmission electron microscopy has made to the understanding of the mobility and clustering of point defects in fcc and bcc metals. The first part of the paper considers the nucleation and growth of vacancy clusters in quenched fcc metals. In the second part the complex subject of irradiation damage is discussed with emphasis being placed on showing the inter-relationship existing between basic damage processes governing defect production and the visible defect structure. The third section discusses the observation of cluster growth and shrinkage in terms of the information they provide about defect mobility. In the final part of the paper a summary is presented of the main conclusions that can be drawn from electron microscope studies regarding the behaviour of vacancy and interstitial defects in fcc and bcc metals.
150 citations
TL;DR: The use of non central empirical potentials and pseudopotentials for point defect energies and configurations in metals has been investigated in this paper, but their agreement with interstitial properties is still uncertain.
Abstract: Interatomic potentials and calculations for point defect energies and configurations in metals are reviewed. Initially semiempirical central two body potentials (Lennard- Jones, Morse, Born-Mayer) were used, but were not found to be very satisfactory. Empirical potentials based primarily on elastic constant data have been more successful for the calculation of vacancy energies but their agreement with interstitial properties is still uncertain. The use of non central empirical potentials and pseudopotentials is still under investigation.
150 citations
TL;DR: In this article, single crystal aluminium surfaces were prepared by auto-epitaxy on these substrates and the work functions of the surfaces were determined photoelectrically, showing a linear relationship between surface atom density and work function for the three faces investigated.
Abstract: (100), (110) and (111) single crystal aluminium substrates were thoroughly outgassed by heating by electron bombardment in ultra high vacuum. Fresh single crystal surfaces were prepared by autoepitaxy on these substrates and the work functions of the surfaces were determined photoelectrically. The general effect of the deposition of an aluminium film on the substrate was to reduce the work function, but annealing the film at temperatures between 473 K and 573 K caused the work function to return to a constant value which was taken to be characteristic of the ordered surface. (100) aluminium surfaces were also prepared by epitaxy on potassium chloride crystals. The effect of argon ion bombardment on a bulk (110) aluminium surface is to increase the work function towards the polycrystalline value, but the characteristic value for the (110) face may be restored by annealing the crystal. There is a linear relationship between surface atom density and work function for the three faces investigated.
140 citations
TL;DR: In this article, the self energy expression obtained from a Ward identity has a simple alternative diagrammatic derivation in terms of electron-magnon scattering processes and the question of the stability of strong ferromagnetism in the Hubbard model is considered.
Abstract: For pt. I, see ibid., vol.3, no.12, 2174 (1973). The strongly ferromagnetic limit of the theory developed in the preceding paper is examined in detail. The self energy expression obtained there from a Ward identity has a simple alternative diagrammatic derivation in terms of electron-magnon scattering processes. General features of the resultant single particle excitation spectrum are investigated and the question of the stability of strong ferromagnetism in the Hubbard model is considered. Numerical calculations of self energies, spectral weight functions and densities of states are presented for a simple spherically symmetric band structure whose parameters are chosen to simulate the band structure of nickel. Experimental implications of the work are discussed.
110 citations
TL;DR: A review of the present state of understanding of the defect reactions occurring during the annealing of irradiated metals is given in this article, where the authors show that single vacancies become mobile in stage III and annihilate at the interstitial clusters remaining from lower temperatures.
Abstract: A review of the present state of understanding of the defect reactions occurring during the annealing of irradiated metals is given. These reactions are presently understood best for recovery stage 1. In this stage-aside from close pair recovery-freely migrating interstitials react with vacancies, other interstitials and impurity traps. Stage II annealing involves primarily the rearrangement of the interstitial clusters nucleated in stage I. Growth of larger clusters is obtained at the expense of smaller ones. In addition, in samples where extensive trapping of interstitials at impurities has occurred in stage I, detrapping of the interstitials from these impurities is observed in stage II. For a number of metals there is now clear evidence that single vacancies become mobile in stage III and annihilate at the interstitial clusters remaining from lower temperatures.
TL;DR: In this paper, the requirements of spin conservation in the form of a Ward identity, are exploited to make a selfconsistent theory of itinerant ferromagnetism in terms of electron-magnon interactions.
Abstract: The requirements of spin conservation in the form of a Ward identity, are exploited to make a selfconsistent theory of itinerant ferromagnetism in terms of electron-magnon interactions. Earlier results are extended to weak ferromagnets and the structure of self energies and single particle spectral weight functions is discussed. The theory is also applied to the calculation of the spin wave stiffness constant.
TL;DR: In this article, the progress made at Cornell University over the past few years in applying the field ion microscopy (FIM) technique to the study of point defects in irradiated or quenched metals is reviewed.
Abstract: The progress made at Cornell University over the past few years in applying the field ion microscopy (FIM) technique to the study of point defects in irradiated or quenched metals is reviewed. The techniques involve essentially the atom by atom dissection of specimens by pulse field evaporation and the corresponding recording on film of the extensive number of FIM images produced at each stage of the process. The application of these techniques to the following problems are discussed: (i) the mobility of self interstitial atoms (SIA) in substage IE of irradiated tungsten and platinum, (ii) the geometric configuration of the SIA, (iii) the point defect structure of depleted zones in tungsten and (iv) the properties of monovacancies and divacancies in quenched platinum.
TL;DR: In this article, an improved form of the optimized model potential is described in which non-locality is treated fully and effective masses and exchange-correlation corrections are included, and tables of the on-Fermi-sphere matrix elements of the model potential and the energy-wavenumber characteristic are given for 33 elements, although it is recommended that for numerical work Chebyshev polynomial expansions should be used.
Abstract: An improved form of the optimized model potential is described in which nonlocality is treated fully and effective masses and exchange-correlation corrections are included. Tables of the on-Fermi-sphere matrix elements of the model potential and the energy-wavenumber characteristic are given for 33 elements, although it is recommended that for numerical work Chebyshev polynomial expansions should be used.
TL;DR: In this article, the mass enhancement factor for ten transition metals (Zr, Nb, Mo, Ta, W, Re, Rh, Pd, Ir and Pt) was calculated using information available from band structure calculations, neutron scattering experiments and a simple theory of the electron-phonon coupling.
Abstract: Using information available from band structure calculations, neutron scattering experiments and a simple theory of the electron-phonon coupling. The mass enhancement factor lambda is calculated for ten transition metals: Zr, Nb, Mo, Ta, W, Re, Rh, Pd, Ir and Pt. For the superconducting elements the results are in good qualitative and in reasonable quantitative agreement with the empirical values of lambda obtained from data on the superconducting transition temperature. The magnitude of lambda in the nonsuperconducting metals is discussed.
TL;DR: In this article, the core structures of six nonscrew 1/2(111) dislocations lying on a (110) plane have been made using three different central inter-atomic forces.
Abstract: Atomistic calculations of the core structures of six different nonscrew 1/2(111) dislocations lying on a (110) plane have been made using three different central inter-atomic forces. The cores of all the dislocations studied have been found to be similar: planar, confined to a single (110) plane. The results are, therefore, interpreted in terms of a density of the Burgers vector in this plane. The determination of the core structure by both the type of the crystal lattice and assumed interatomic forces is discussed in terms of restoring forces for (110) planes which well characterize the strength of binding in a given crystal structure.
TL;DR: In this article, the lattice parameters of the face centred cubic forms of rare earth metals, Gd, Tb, Dy, Ho, Er and Tm were found respectively to be 5.40, 5.20, 5 18, 5 15, 5 14, 5 12, 5 11, 5 8.09 and 5.06 AA the error being about +or 1%.
Abstract: High energy transmission electron diffraction and microscope studies have been made of the following rare earth metals, Gd, Tb, Dy, Ho, Er and Tm, the films being made by means of vapour deposition. The thinnest films had face centred cubic structures whereas in the thicker films the hexagonal close packed structures of the metals in bulk form were observed. Oxidation of the films was observed in the vacuum in which they were deposited and also under the influence of the electron beam of the electron microscope. The lattice parameters of the face centred cubic forms of Gd, Tb, Dy, Ho, Er and Tm were found respectively to be 5.40, 5.20, 5.18, 5.15, 5.09 and 5.06 AA the error being about +or-1%.
TL;DR: In this article, specific heat measurements between 1.5 K and 15 K on a large number of alloys in the range of existence of the Ni3Al and Ni3Ga intermetallic phases are reported.
Abstract: Results of specific heat measurements between 1.5 K and 15 K on a large number of alloys in the range of existence of the Ni3Al and Ni3Ga intermetallic phases are reported. For four Ni3Ga samples the measurements were extended down to 0.2 K, and the effect of various heat treatments on the specific heat was measured on two Ni3Ga samples. The results, especially their concentration dependence, definitely exclude the presence of any appreciable contribution of the form predicted for paramagnon enhancement, but an interpretation in terms of superparamagnetic clusters also runs into serious difficulties.
TL;DR: In this paper, the authors calculated the extraordinary Hall effect induced by cerium impurities for which the conduction electron-impurity interaction is mainly due to resonant scattering and compared the results with experimental data on La-Ce alloys.
Abstract: Skew scattering by magnetic impurities in dilute magnetic alloys induces an extraordinary Hall effect which has now been observed in many systems. The author calculates the extraordinary Hall effect induced by cerium impurities for which the conduction electron-impurity interaction is mainly due to resonant scattering. The results are compared with experimental data on La-Ce alloys. The anisotropy of the magneto-resistance of such alloys is calculated and compared with some preliminary experimental results.
TL;DR: In this article, a simplified method for determining the Rayleigh velocity of surface waves in arbitrarily anisotropic crystals is developed, which is the velocity at which the smaller of the eigenvalues of a certain 2*2 real symmetric matrix vanishes.
Abstract: Using a knowledge of the close connection between elastic surface waves and uniformly moving straight dislocations, a simplified method for determining the Rayleigh velocity of surface waves in arbitrarily anisotropic crystals is developed. It is shown that the Rayleigh velocity is that velocity at which the smaller of the eigenvalues of a certain 2*2 real symmetric matrix vanishes. The matrix elements can be accurately determined by simple numerical integration and correspond, in fact, to submatrix elements of the prelogarithmic lagrangian factor matrix for a straight dislocation moving in a plane parallel to the surface and in the direction of propagation of the Rayleigh wave. In addition, a scheme is developed for determining the polarization vector of the surface wave using numerical integration. Hence, the method circumvents the need for numerically solving sextic equations and constructing associated eigenvector sets common to more conventional approaches to the surface wave problem. The numerical efficiency of the scheme is illustrated for the case of cubic symmetry.
TL;DR: In this article, the electronic densities of states functions for the random substitutional alloy system Ag-Pd for a number of compositions across the complete range of concentrations are calculated based on the coherent potential approximation.
Abstract: Electronic densities of states functions are calculated for the random substitutional alloy system Ag-Pd for a number of compositions across the complete range of concentrations. The calculations are based on the coherent potential approximation. It was found necessary to extend the simple model Hamiltonian method previously used to describe Cu-Ni alloys because of the stronger dependence of the lattice constant on composition in the Ag-Pd system. It is shown that the results are consistent with published photoemission and optical absorption data, and low temperature specific heat and Pauli spin susceptibility experiments. The possibility of s-d charge transfer in this alloy system is discussed.
TL;DR: In this paper, the Thomas-Fermi approximation is applied to calculate the electron charge distributions of vacancies and edge dislocations in aluminium within the jellium model, and a method is derived to evaluate the momentum dependent annihilation rate in a nonuniform electron gas.
Abstract: The Thomas-Fermi approximation is applied to calculate the electron charge distributions of vacancies and edge dislocations in aluminium within the jellium model. The various factors affecting positron trapping, at crystal defects are discussed. A method is derived to evaluate the momentum dependent annihilation rate in a nonuniform electron gas. The calculation gives a value of 24% of the bulk value for the electron density at the centre of a vacancy. The annihilation characteristics are calculated for the trapped positron, and a good agreement with experimental results is established. An edge dislocation is described by a hollow core model. The hole radius of 0.85 AA is found to reproduce the experimental lifetime of positrons in deformed aluminium. The electron density at the centre of the dislocation core reduces to 37% of its value in the bulk material. The momentum distributions of the annihilation quanta are calculated for various dislocation orientations, and a remarkable anisotropy in angular correlation curves is found.
TL;DR: In this article, a simple microscopic formulation of this model is presented, applied to discuss such pertinent electronic properties as the density of carrier energy states, the specific heat, the paramagnetic susceptibility and the static dielectric constant.
Abstract: Mixed valency planar complex compounds of Pt have been recently identified as quasi one dimensional metals on the basis of a phenomenological model that views the real crystalline compound to consist of a system of collinear metallic strands, each of which is interrupted by a series of insulating lattice defects. An originally defect free strand is thereby replaced by a linear sequence of one dimensional metallic boxes. In the present paper a very simple microscopic formulation of this model is presented. It is applied to discuss such pertinent electronic properties as the density of carrier energy states, the specific heat, the paramagnetic susceptibility and the static dielectric constant.
TL;DR: In this article, the effects of electromigration in 525 AA Au films were studied by transmission electron microscopy during the actual passage of current, and an activation energy of 0.8 eV was calculated from the rate of void growth.
Abstract: Electromigration in 525 AA Au films has been studied by transmission electron microscopy during the actual passage of current. The effects of electromigration were the growth of voids near the cathode end and the growth of hillocks near the anode end of the test strip. The hillocks were rounded in shape with heights up to 40* the average thickness of the films. An activation energy of 0.8 eV was calculated from the rate of void growth.
TL;DR: In this article, a simple overlayer structure leading to a dense compact monolayer arrangement was found and evidence was then found for the formation of an alloy layer which appears spontaneously at room temperature after completion of the first dense monolayers.
Abstract: Auger electron spectroscopy and low energy electron diffraction have been used to study monolayers of lead deposited in ultrahigh vacuum on to the (100) face of gold. There form first simple overlayer structures leading to a dense compact monolayer arrangement. Evidence is then found for the formation of an alloy layer which appears spontaneously at room temperature after completion of the first dense monolayer. The proposed alloy structure has the composition AuPb3.
TL;DR: In this article, the static lattice distortion and relaxation energy for nitrogen and oxygen inter-stitials at octahedral and tetrahedral sites in niobium, tantalum and vanadium have been calculated by using the Green function method for lattice statics.
Abstract: The static lattice distortion and relaxation energy for nitrogen and oxygen inter- stitials at octahedral and tetrahedral sites in niobium, tantalum and vanadium have been calculated by using the Green function method for lattice statics. The forces responsible for the lattice distortion have been obtained from the measured values of the dipole tensor, which avoids the need for a priori knowledge of the gas-host potential. However. simple functions for the 'effective' gas-host interaction have been fitted to the calculated values of the atomic displacements which should be useful for further calculations on these systems.
TL;DR: The Heine-Abarenkov model potential for metals was developed by Shaw (1968) to avoid arbitrary choice of the model radius as mentioned in this paper, and the parameters have been calculated for a large number of the metallic elements in each case including selfconsistent iteration through the calculated shifted Fermi level.
Abstract: The Heine-Abarenkov model potential for metals was developed by Shaw (1968) to avoid arbitrary choice of the model radius. Here the parameters have been calculated for a large number of the metallic elements in each case including selfconsistent iteration through the calculated shifted Fermi level. The expressions used in the calculations are discussed and results are presented of the Fermi level calculations together with selfconsistent optimized model potential parameters and their energy derivatives.
TL;DR: In this paper, the anomalous properties of a cold sapphire film are attributed to structural disorder and analyzed in terms of a two phase model using a two-phase model.
Abstract: Silver films formed on a cold sapphire substrate and studied prior to annealing exhibit a very different optical absorption from that typical of an annealed silver film. In particular a film formed and studied at 140 K showed a greatly reduced plasmon energy and a large anomalous absorption band centred at 2.4 eV. Annealing the film at RT caused a return to properties typical of an annealed film, although small but distinct differences remained between the Drude behaviour of the two films formed at different temperatures. The anomalous properties of the cold film are ascribed to structural disorder. The behaviour is analysed in terms of a two phase model.
TL;DR: In this article, the magnetic hyperfine field and isomer shift measurements in Y(Fe1-xCox)2 and Ho(Fe 1-xCoX)2 intermetallic compounds are reported, and the changes in these quantities with concentration are related to changes in the d moment and in the lattice parameter.
Abstract: Magnetic hyperfine field and isomer shift measurements in Y(Fe1-xCox)2 and Ho(Fe1-xCox)2 intermetallic compounds are reported, and the changes in these quantities with concentration are related to changes in the d moment and in the lattice parameter. The origin of the 57Fe hyperfine fields and the proportionality between field and magnetic moment are discussed using a simple model. The Mossbauer spectra of the Y(Fe1-xCox)2 compounds show that the direction of magnetization changes from a (111) axis (in YFe2) to (101) in the samples with x>or=0.17.
TL;DR: In this paper, the Peierls stresses of 1/2(111) non screw dislocations, the core structures of which were studied in part I, were calculated by positioning the dislocation in various crystallographically non equivalent positions and by simulation of the dislocations in a crystallite subject to an external stress.
Abstract: For pt.I, see ibid., vol.5, no.1, 1 (1975). The Peierls stresses of 1/2(111) non screw dislocations, the core structures of which were studied in part I, were calculated (1) by positioning the dislocation in various crystallographically non equivalent positions and (2) by simulation of the dislocation in a crystallite subject to an external stress. The first method is inadequate since it overestimates the Peierls stress and does not show any asymmetry connected with the twinning and antitwinning sense of shear. The results are compared with those for non screw dislocations on (110) planes and for the screw dislocation.