Showing papers in "Journal of Physics F: Metal Physics in 1971"
TL;DR: In this article, the interstitial hydrogen contents and their associated volume increments have been determined for a variety of fcc metals and alloys using high pressure techniques, where hydrogen contents approaching n = 1, where n = H-to-metal (atomic ratio), have been obtained.
Abstract: Interstitial hydrogen contents and their associated volume increments have been determined for a variety of fcc metals and alloys. Using high pressure techniques, hydrogen contents approaching n = 1, where n = H-to-metal (atomic ratio), have been obtained. Despite electronic and initial volume differences amongst the fcc metallic matrices, all data fall onto a common relationship.
268 citations
TL;DR: In this paper, a procedure which involves the sampling of ordering space at discrete points is described and applied to various alloys, which is a first step towards a more systematic interpretation of the experimental data.
Abstract: X ray and neutron diffraction analysis may give only limited information about the ordering of the atoms in Heusler alloys. As a first step towards a more systematic interpretation of the experimental data, a procedure which involves the sampling of ordering space at discrete points is described and applied to various alloys.
85 citations
TL;DR: In this paper, the relative energies of the fcc, bcc, and hcp structures of the alloy systems CuAl, LiMg, and CuZn are calculated with a realistic local pseudopotential model and it is suggested that the attractive forces arising from the overlap of neighbouring d electrons and from their Van der Waals interactions provide a substantial impetus for a distorted structure in Zn.
Abstract: The hypothesis that Hume-Rothery's rules for phase stability in binary alloys are a consequence of the divergent slope of the wave-number-dependent dielectric function at 2kF is investigated. The relative energies of the fcc, bcc, and hcp structures of the alloy systems CuAl, LiMg, and CuZn are calculated with a realistic local pseudopotential model. Striking evidence of the screening anomaly is obtained in all cases. The calculations suggest alloy phase boundaries in the three systems studied which are for the most part in excellent agreement with experiment. The only exceptions are pure Cu and pure Zn, for which an incorrect structure is predicted, the former by a remarkably small 3 × 10-5 ryd per electron. It is suggested that both discrepancies might be rectified if the forces between d electrons on neighbouring sites were properly accounted for. In particular, it is argued that the attractive forces arising from the overlap of neighbouring d electrons and from their Van der Waals interactions provide a substantial impetus for a distorted structure in Zn. A thermodynamic instability arising from the divergent slope of the dielectric function is considered. Rough calculations are presented which indicate that when higher order terms in the electron-ion interaction are properly considered this instability will disappear, without, however, the phase boundaries being significantly altered. The principal conclusion, which is consistent with previous suggestions, is therefore that the Hume-Rothery rule arise not so much from the screening divergence itself as from the rapid variation of the dielectric function in the immediate vicinity of 2kF.
76 citations
TL;DR: In this paper, a general method of calculating the energy per defect in the array which exploits the periodicity of the defect lattice is presented, and the results predict that a void lattice should occur in molybdenum and compare a number of models for the void.
Abstract: Defects in crystals may form a regular array, rather than a random distribution. The lattice of voids produced in irradiated molybdenum is a remarkable example of this. We give a general method of calculating the energy per defect in the array which exploits the periodicity of the defect lattice. The existence of the void lattice depends on the elastic interaction between voids. The present approach can treat both arbitrarily anisotropic elastic continua and discrete lattices, and is readily extended to discuss the stability of the defect lattice. The results predict that a void lattice should occur in molybdenum, and compare a number of models for the void. Stability against shear of the void lattice is not discussed in the present paper. The ratio of the void lattice spacing to void radius predicted is 2.2 to 4.5 and is smaller than the value of about 10 observed. The results are in general agreement with the more approximate Malen-Bullough treatment.
58 citations
TL;DR: In this article, it is argued that a major contribution to this breadth at infinite dilution is the spin orbit splitting of the d levels; the resonance broadening, 2? on the Anderson model, being estimated as 0.185 eV-1 per atom.
Abstract: Photoemission experiments have been made on a series of AgPd alloys including the pure components. In Ag-rich alloys the d levels of the Pd atoms occupy a resonant bound state which has a width similar 1 eV at infinite dilution increasing to similar 1.7 eV at 30% Pd. It is argued that a major contribution to this breadth at infinite dilution is the spin orbit splitting of the d levels; the resonance broadening, 2? on the Anderson model, being estimated as 0.5 eV. The increase in breadth with increasing Pd content is attributed to interatomic d-d broadening between Pd atoms. The isolated impurity atom is believed to possess similar 0.38 d holes and contribute to the density of states at the Fermi level an amount similar 0.185 eV-1 per atom. These values are compatible with other properties of AgPd alloys namely the electron specific heat and residual electrical resistance. Comparison is made with the analogous CuNi alloys. Above 40% Pd the d electrons occupy true band states and it is suggested that the transition from the resonant bound state to the band state is sharp and may be characterized as a semiconductor-metal transition for the Pd d electrons. The experimental data clearly show the effects of structural disorder on the sharp band structures of the pure components. In the case of PdAg alloys the blurring of the band structure due to disorder and the transference of electrons from Ag conduction to Pd d states on account of the weak screening of the Ag impurity atoms account for the rapid decrease in electron heat and paramagnetic susceptibility of Pd due to alloying with Ag. Direct transitions between conduction band states, capital Lambda1-capital Lambda1 transitions, were observed in pure Ag and the Ag0.95Pd0.05 alloy.
58 citations
TL;DR: In this article, the steady state measurements of the quasiparticle lifetime (τ) in superconducting aluminium were published previously, and it was shown that the effect of heating on the lifetime measurements is negligible at low temperatures and can be accounted for near the transition temperature (Tc).
Abstract: We report details of the steady state measurements of the quasiparticle lifetime (τ) in superconducting aluminium which were published previously. We begin with a synopsis of the relevant background, followed by an explanation of our experimental procedure. Included are some aspects of the experiments not primarily related to the lifetime measurements. It is shown that the process responsible for the excess current found by Burstein and Taylor in aluminium tunnel junctions for Δ 4Δ we observe enhanced injection of quasiparticles. We show that the effect of heating on the lifetime measurements is negligible at low temperatures and can be accounted for near the transition temperature (Tc). Near Tc there is another recombination process in which the excess energy is absorbed by another quasiparticle. Very near Tc there are indications that τ becomes very long. As the temperature decreases much below Tc, τ approaches a constant value due to recombination in regions of flux penetration.
55 citations
TL;DR: A detailed study of the diffuse scattering in the neutron diffraction patterns of single crystals of γ MnCu alloys containing 10, 15, 25 and 40 at% Mn has shown that diffuse peaks occur at the 1½0 type positions, and are due to both atomic and magnetic short range ordering as discussed by the authors.
Abstract: A detailed study of the diffuse scattering in the neutron diffraction patterns of single crystals of γ MnCu alloys containing 10, 15, 25 and 40 at% Mn has shown that diffuse peaks occur at the 1½0 type positions, and are due to both atomic and magnetic short range ordering. Analysis of the diffuse scattering has yielded the atomic and magnetic short range order parameters and a value of S = 2.0 ± 0.3 for the localized spin on the manganese site. Neutron diffraction measurements of polycrystalline specimens have also confirmed that dilute γ MnCu alloys containing 3, 8, 15 and 25 at% Mn show no evidence of co-operative magnetic ordering at temperatures down to 4.2K. It is suggested that earlier results from Mossbauer and electron spin resonance experiments can be reconciled with the neutron diffraction results by invoking a model in which there is a non-zero temporal average of the spins rather than long range spatial magnetic ordering.
49 citations
TL;DR: In this article, the resistivity at temperatures below 4.2 K of palladium alloys with 2 to 6 at% nickel has been measured and fitted to the expression ρ - ρ0 = ATn.
Abstract: The resistivity (ρ) at temperatures below 4.2 K of palladium alloys with 2 to 6 at% nickel has been measured and fitted to the expression ρ - ρ0 = ATn. The behaviour of A clearly indicates the critical concentration for the para- to ferromagnetic transition at 2.32 ± 0.03 at% nickel. Well away from this composition n is close to 2.0, but decreases on approaching it from either side.
42 citations
TL;DR: A modified Einstein-de Hass method has been developed sufficiently sensitive to measure the gyromagnetic ratio g' in paramagnetic transition metals as discussed by the authors, showing a large orbital magnetism in V, Cr, Nb and Ta.
Abstract: A modified Einstein-de Hass method has been developed sufficiently sensitive to measure the gyromagnetic ratio g' in paramagnetic transition metals. For the metals investigated the experimental values are Vanadium g' = 1.18 ± 0.10 Chromium g' = 1.21 ± 0.07 Niobium g' = 1.05 ± 0.07 Tantalum g' = 1.02 ± 0.07 Palladium g' = 1.77 ± 0.10 Platinum g' = 1.62 ± 0.08 From these values the contributions from orbital and spin effects can be resolved, showing a large orbital magnetism in V, Cr, Nb and Ta.
41 citations
TL;DR: In this paper, the frequencies of phonons with reduced wavevectors in the, and directions of the reciprocal lattice, and polarized in one of the mirror planes are reported for antimony at room temperature.
Abstract: Inelastic neutron scattering measurements are reported of the frequencies of the normal modes of vibration of antimony at room temperature. Results are presented for the frequencies of phonons with reduced wavevectors in the , and directions of the reciprocal lattice, and polarized in one of the mirror planes. Bornvon Karman models with general tensor forces extending to the ninth-nearest neighbours of each atom are unable to fit the data to within the accuracy of the measurements. Comparisons are made with phonon dispersion curves for bismuth by scaling all frequencies with the ionic plasma frequency. Marked differences between the scaled dispersion curves at small wavevectors are attributed to the effects of spin-orbit coupling on the wavevector dependence of the dielectric constant. At the zone boundaries, the phonon frequencies are less sensitive to details of the screening, but it seems important to include the effects of covalency if calculations of the phonon frequencies are to agree with experiment.
40 citations
TL;DR: In this article, a method of obtaining expressions for the magnetoconductivity tensor for group V semimetals, valid over the classical range of magnetic fields, is given.
Abstract: A method of obtaining expressions for the magnetoconductivity tensor for group V semimetals, valid over the classical range of magnetic fields, is given. Explicit expressions are derived for the elements of the tensor appropriate to antimony and arsenic for B along each of the three principal crystallogrpahic directions.
TL;DR: In this article, the authors examined the decrease in superconducting critical temperature Tc with impurity concentration nI for dilute magnetic alloys in the framework of the Kondo-Nagaoka theory.
Abstract: The decrease in superconducting critical temperature Tc with impurity concentration nI is examined for dilute magnetic alloys in the framework of the Kondo-Nagaoka theory. When the critical temperature Tco of the host metal is much larger than the Kondo temperature TK the curves of Tc versus nI behave in the manner predicted by the Born approximation theory of Abrikosov and Gorkov, except for an exponential tail for Tc << TK. When Tco << TK these curves show a non-magnetic behaviour which is related to the theory of the Suhl-Nagaoka spin compensated state. The theory is compared to (i) experimental data for LaCe and ThU and (ii) the theory of localized spin fluctuations which provides an alternative explanation for the data.
TL;DR: In this paper, the authors present measurements of thermoelectric power for nickel and cobalt dilute alloys with d transition elements in two temperature ranges: from 1.3 to 4.2 K and from 77 to 300 K. The results of the measurements at room temperature in a two-band conduction model and deduce the thermopowers associated with the matrix (Smσ) and with the impurities (Soσ) in each sub-band σ.
Abstract: We present new measurements of thermoelectric power for nickel and cobalt dilute alloys with d transition elements in two temperature ranges: from 1.3 to 4.2 K and from 77 to 300 K. We analyse the measurements at room temperature in a two-band conduction model and deduce the thermopowers associated with the matrix (Smσ) and with the impurities (Soσ) in each sub-band σ. The results obtained for the impurity thermoelectric power confirm the model of electronic structure suggested for this alloy from magnetization and resistivity measurements; this model is characterized by the occurrence of a virtual bound state supward arrowdupward arrow at the Fermi level when the charge difference between the matrix and the impurity is large enough. From the values of impurity thermoelectric power in the supward arrow sub-band, we deduce the position and the width of the virtual bound state.
TL;DR: In this paper, the electronic structure of dilute alloys of noble or transition metals, in a modified Slater-Koster model, is studied, where the pure metal band structure is described by an interpolation scheme of hybridized tight binding and nearly free electron orbitals.
Abstract: We study the electronic structure of dilute alloys of noble or transition metals, in a modified Slater-Koster model. The pure metal band structure is described by an interpolation scheme of hybridized tight binding and nearly free electron orbitals. The matrix elements of impurity potential between `s' basis functions are treated by a perturbation method. Within these approximations, we obtain exact formulae for the Green functions of the alloy, and for the displaced charge. We discuss specially the displaced charge, the transition matrix t, and the residual resistivity in the case of a potential localized on its own cell. We present the results of a numerical study of CuNi alloy.
TL;DR: In this paper, the high energy side of the main (L2,3VV) Auger line is interpreted as a plasmon gain. This line also exhibits a large (13eV) chemical shift.
Abstract: Measurements are reported on the Auger and characteristic energy loss spectra of evaporated Al both for clean aluminium and as residual oxygen is absorbed on the surface. Fine structure on the high energy side of the main (L2,3VV) Auger line is interpreted as a plasmon-gain. This line also exhibits a large (13eV) chemical shift.
TL;DR: In this paper, precision measurements of the angular distribution of annihilation photons have been performed on samples of carefully annealed cadmium metal and the results provided a value of 0.52 ± 0.05 eV for the activation energy for vacancy formation in Cadmium and emphasise the importance of core annihilation in the study of positron behaviour in metals.
Abstract: The strong temperature dependence of positron lifetimes in some metals has been explained in terms of the trapping of positrons by vacancies. To test the model further, precision measurements of the angular distribution of annihilation photons have been performed on samples of carefully annealed cadmium metal. The results, which are analysed in terms of the trapping model, provide a value of 0.52 ± 0.05 eV for the activation energy for vacancy formation in cadmium and emphasise the importance of core annihilation in the study of positron behaviour in metals.
TL;DR: In this paper, the frequencies in zinc at 80 K have been determined for all symmetry lines in wavevector space, using a neutron crystal spectrometer using dispersion curves and in table form.
Abstract: Phonon frequencies in zinc at 80 K have been determined for all symmetry lines in wavevector space, using a neutron crystal spectrometer. The results, which are complete and of good accuracy, are presented as dispersion curves and in table form
TL;DR: The magnetic and structural parameters of pseudobinary rare earth and transition metal compounds are reported in this paper, and the final values are given by a bootstrap process which depends upon the initial rare earth moment and the detailed structure of the 3d-electron band in these materials.
Abstract: The magnetic and structural parameters of a number of pseudobinary rare earth and transition metal compounds are reported. These all belong to the cubic Laves phase C15 structure and have the general formula R(Fe, Co)2 and R(Co, Ni)2 where R includes Nd, Gd, Dy, Ho and Er. The magnetic behaviour suggests that the magnitudes of the rare earth and transition metal ionic moments change rapidly at compositions to the nickel side of the pure RCo2 compound. It is suggested that these changes are interdependent and the final values are given by a bootstrap process which depends upon the initial rare earth moment and the detailed structure of the 3d-electron band in these materials.
TL;DR: In this paper, the authors measured the thermoelectric power of a number of Au-Fe alloys, with Fe concentrations between similar 10 and 1900 ppm, and found that the thermopower of all but the most dilute alloys shows an initial increase in magnetic field, which is caused by Fe-Fe interactions.
Abstract: We have measured the thermoelectric power of a number of Au-Fe alloys, with Fe concentrations between similar 10 and 1900 ppm. Measurements were made between 0.4 and 30 K in fields up to 70 kOe. The alloys exhibited the familar `giant' thermopower in zero field, the peak value observed being - 15 μ V K-1 at about 10 K. Both the order of magnitude and the temperature dependence of the zero-field thermopower agree fairly well with Kondo's theory of spin-flip scattering. The thermopower of all but the most dilute alloys shows an initial increase in a magnetic field, which we believe is caused by Fe-Fe interactions. The thermopower then decreases due to `freezing-out' of spin-flip scattering and a simple pair-interaction model accounts for most of this observed behaviour. For the most concentrated alloy the decrease is not observed, even for the maximum field applied. For still higher fields (and lower concentrations) the thermopower decreases approximately as 1/H, as is suggested by a recent perturbation calculation.
TL;DR: In this paper, the Auger and characteristic energy loss spectra of clean Be have been taken with a three grid retarding field analyser and changes in the spectrum caused by the chemisorption of residual oxygen have been observed.
Abstract: The Auger and characteristic energy loss spectra of clean Be have been taken with a three grid retarding field analyser Also changes in the spectrum caused by the chemisorption of residual oxygen have been observed
TL;DR: In this paper, the density of states of the liquid transition metals, iron and copper, was evaluated by applying the analysis of Lloyd to clusters of several atoms, and the results were analyzed with a simple potential model and compared with those of the crystalline solids.
Abstract: The density of states of the liquid transition metals, iron and copper, is evaluated by applying the analysis of Lloyd to clusters of several atoms. The results are analysed with a simple potential model and compared with those of the crystalline solids.
TL;DR: In this paper, the phase shifts of muffin-tin potentials are used to construct the t-matrix of a single scattering center, which is then used to calculate the resistivity and thermopower of noble metals.
Abstract: Numerical calculations based on the Ziman nearly free electron theory of the resistivity and thermopower of the noble metals are presented. The phase shifts of muffin-tin potentials are used to construct the t-matrix of a single scattering centre. Good agreement with experiment is achieved.
TL;DR: In this paper, the conduction and core bands, density of states, Fermi energy and surface of Ca were computed for an optimum value of the exchange and it was found that the surface of the surface is connected and agreement with all the known results of the de Haas-van Alphen effect.
Abstract: The conduction bands for Ca have been computed with a Slater-type potential and it is found that for less than 20% or more than 75% of the exchange term there is no overlap between the first and second band. The conduction and core bands, density of states, Fermi energy and Fermi surface are computed for an optimum value of the exchange. It is found that the Fermi surface is connected and agreement with all the known results of the de Haas-van Alphen effect is obtained. Although this is in apparent disagreement with the results of Vasvari et al. who obtain an unconnected Fermi surface, their Fermi level was wrongly located and when the error is corrected a connected surface should almost certainly be obtained. The effect of pressure on the Fermi surface and conductivity of Ca is discussed.
TL;DR: In this article, the authors show that at high temperature, Li's constant volume resistivity becomes larger than the zero (atmospheric) pressure value, which is contrary to what is observed in the other alkalis.
Abstract: In Li, at high temperature, the constant volume resistivity becomes larger than the zero (atmospheric) pressure value. This is contrary to what is observed in the other alkalis. It has been suggested that it is a result of an increase in the distortions of the lithium Fermi surface with application of hydrostatic pressure. We show that the effect can be understood much more simply and naturally on the basis of a spherical Fermi surface and a simple electron-ion pseudopotential form factor. The form factor is used to evaluate the absolute value and the volume dependence of the thermoelectric power. the thermal conductivity and the electron-phonon mass renormalization.
TL;DR: The recoil-free fractions in the 14.4 keV Mossbauer gamma line of 57Fe from 30 different host lattices have been determined using the black absorber technique as mentioned in this paper.
Abstract: The recoil-free fractions in the emission of 14.4 keV Mossbauer gamma line of 57Fe from 30 different host lattices have been determined using the black absorber technique. The force constants between the impurity-host and host-host atoms are found to be within about 20% equal for most of the hosts. For Pd the force constants between impurity-host atoms remain relatively unchanged up to 5 wt% of the impurity. In Pb, Tl and In the impurity atoms appear to diffuse into interstitial positions.
TL;DR: In this article, the photoemitted electron distributions from Cu, Zn and β'-CuZn up to 21 eV photon energy were measured and it was shown that the Cu d-band is 0.9 eV lower relative to the Fermi level in β'-cuZn than in pure Cu and the width is only slightly smaller.
Abstract: Measurements on photoemitted electron distributions from Cu, Zn and β'-CuZn up to 21 eV photon energy are reported. It is found that the Cu d-band is 0.9 eV lower relative to the Fermi level in β'-CuZn than in pure Cu and the width is only slightly smaller. The Zn d-band however has essentially the same position in both Zn and β'-CuZn. It is shown that the Cu d-states are responsible for the yellow colour of β'-CuZn rather than the conduction states as has been previously proposed.
TL;DR: In this article, the relaxation times for electrons on the Fermi surface of Ag due to scattering from dilute concentrations of Au and Cu impurities were calculated and shown to depend critically on cancellation between potential scattering and relativistic scattering and possibly the effects of the strain field.
Abstract: Calculations have been made of the relaxation times for electrons on the Fermi surface of Ag due to scattering from dilute concentrations of Au and Cu impurities. In the case of AgAu alloys it has been found that the relaxation times are primarily determined by the mass-velocity and Darwin relativistic corrections to the potential seen by an electron. In AgCu alloys the relativistic corrections are still important and the calculated relaxation times depend critically on cancellation between `potential' scattering and `relativistic scattering' and possibly the effects of the strain field.
TL;DR: A study of the nuclear magnetic resonance spectrum of single crystals of three alloys of aluminium containing 0.5 at% Mg, Ga and Ge impurities respectively has revealed the presence of weak satellite lines whose dependence upon the orientation of the crystal in the magnetic field establishes that they originate at host sites which are nearest neighbours to the impurity as discussed by the authors.
Abstract: A study of the nuclear magnetic resonance spectrum of single crystals of three alloys of aluminium containing 0.5 at% Mg, Ga and Ge impurities respectively has revealed the presence of weak satellite lines whose dependence upon the orientation of the crystal in the magnetic field establishes that they originate at host sites which are nearest neighbours to the impurity. The Ga and Ge results contradict the earlier interpretation of Minier based upon pure quadrupole resonance studies and the new assignment is in greatly improved agreement with the theoretical calculations of Fukai and Watanabe.
TL;DR: In this paper, the effects of transition metal and rare earth substitution into the pseudo-binary alloy system CeRu2-xCox were compared and discussed, and it was concluded that the destruction of the superconductivity in the system is due to localized spin fluctuations associated with the Co.
Abstract: Measurements of the room temperature lattice parameter, the superconducting transition temperature and the magnetic susceptibility over the temperature range 1.5 to 300 K have been made on the pseudo-binary alloy system CeRu2-xCox. Tc is depressed from the values for the terminal compounds and superconductivity could not be detected above similar 0.33 K for 0.2 < x < 1.7. From the form of the variation of Tc with Co substitution and the susceptibility measurements it is concluded that the destruction of the superconductivity in CeRu2 is due to localized spin fluctuations associated with the Co. The effects of transition metal and rare earth substitution into CeRu2 are compared and discussed.
TL;DR: In this article, a local pseudopotential model Hamiltonian with spin effects included in the initial matrix elements was used to fit the existing de Haas-van Alphen (dHvA) data to obtain a band structure with a maximum error of 3 × 10-3 Ryd at a Fermi energy of 0.6110 Ryd.
Abstract: We have parameterized the Fermi surface of thallium by using a local pseudopotential model Hamiltonian with spin effects included in the initial matrix elements. The pseudopotential coefficients are adjusted to fit the existing de Haas-van Alphen (dHvA) data and we find U10macron10 = -0.1058, U0002 = -0.0603, U10macron11 = -0.0429, U10macron12 = -0.0195, λ5p = 0.1130, all in Ryd. These values give a band structure which agrees very well with experiment, having a maximum error of 3 × 10-3 Ryd at a Fermi energy of 0.6110 Ryd. The interpretation by Capocci et al. of their recent dHvA data as due to a fifth zone dumbbell at H is confirmed, and the very small orbits which they observed are reliably assigned to fourth zone pockets along capital GammaM. Recent cyclotron resonance data by Shaw and Everett are shown to agree well with our model. We use our model to calculate magnetic breakdown fields for breakdown across the AHL plane and obtain values reasonably consistent with the existing dHvA data, but much larger than those deduced from the magnetoresistance. We find B0 = 90 kG for the open orbit along [11macron20], whereas Young finds B0 = 10.3 kG by fitting his magnetoresistance data. Our calculations confirm that the fourth zone posts do not contact the capital GammaKM plane, but we find that they are sufficiently close to it for breakdown across the capital GammaKM plane to occur at fields of several hundred kilogauss, thus creating open orbits along [0001].