A model for the lattice dynamics of b.c.c. transition metals

Recent ideas proposed by Fielek for the lattice dynamics of f.c.c. noble and transition metals have been extended to b.c.c. transition metals. Phonon dispersion curves, calculated on the basis of this model, for chromium are in fairly good agreement with experimental ones and are far better than those reported so far.     

On the mechanical stability of bcc transition elements and alloys

A volume independent and a volume dependent lattice energy function involving short-range interatomic potentials were able to be fitted to the elastic constants, cohesive energy, lattice parameter and for the latter function to the vacancy formation energy and bcc-fcc lattice stability energy, as well, for fcc metals and bcc alkali metals, but not to the cohesive energy and C' elastic constant of bcc transition metals. The assumption that directional, but partial, covalent bonds exist between nearest-neighbors in the bcc transition elements provides an explanation for the latter results and in addition explains the identical dependence of C' and the bcc-fcc lattice stability upon N_d, where N_d is the average number of d electrons, for the bcc transition metals and alloys. Both the mechanical and thermodynamic stability of the bcc structure for transition metals and all transition metal alloys disappears for 5 ? N_d > 2 and <?1.     

Zur Zustandsdichte der Übergangsmetalle

X-ray isochromats of the bcc transition metals Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W have been measured with high resolution and under comparable conditions. These curves show, that the rigid-band-model is valid for these metals within one row of the periodic table. The width of the conduction band grows from the 3d- to the 5d-row. These results of the isochromat measurements are compared with conclusions about the density of states at the Fermi level, calculated from values of the electronic specific heat, magnetic susceptibility, and superconducting transition temperature. A comparison with theoretical band calculation shows, that a lowered value of the exchange term in the potential would bring into better agreement the widths of the conduction band, taken from calculation and from isochromat measurements.     

A phenomenological approach for the phonon dispersion curves of barium

A phenomenological model which combines the axially symmetric ion-ion interaction with the electron-ion interaction scheme of Bhatia has been successfully used to calculate the phonon dispersion curves of bcc Ba. In particular, when the elastic constants determined by Mizukiet al are used as input data, the model successfully reproduces the anomalous feature of the dispersion curves measured by them. On the other hand, when the elastic constants determined by Buchenauet al are used, the model produces a cross over of the longitudinal and transverse branches in the [100] direction, a feature not established in their measurements. Thus the features of the dispersion curves in the [100] direction which is due to the hybridization of thes andd states are evident in the measured elastic constants and are consistent with the values of C₁₂-C₄₄.     

The volume dependent total energy of metals and the ionic radii

The cohesive energies, lattice constants and compressibilities for a number of metals are correlated with the ionic radii through second order pseudo-potential theory. The model yields reasonable results not only for simple metals of arbitrary valency, but for transition elements with no more than 5 d-electrons.     

The origin of an elastic line in the L 3 x-ray emission spectrum of metallic manganese

A strong elastic line has been found in the L ₃ x-ray emission spectrum of metallic Mn. To unravel its physical nature, the ground-state properties of α-Mn were studied in comparison with those of 3d metals (Cr and Fe in bcc structure), as well as the properties of the L ₃ absorption final states of these three transition metals. To model the electronic structure, LSDA band-structure calculations of Cr, Mn, and Fe were carried out, and L ₃ absorption spectra of these metals were computed in the atomic approximation. A joint analysis of the properties of the ground state and of the final absorption state excited by an x-ray-produced core hole suggests that the elastic line in the α-Mn spectra should be assigned to the specific character of the absorption final-state multiplet.     

Zur Struktur der Leitungsbänder der kubisch-raumzentrierten Übergangsmetalle

X-ray isochromats of Tantalum, Niobium and Tungsten for different temperatures are presented. They allow a localization of the Fermi edge in the conduction band and show, that the fine structure softens with increasing temperature. This is attributed to a change in the density of states in the conduction band. A modified rigid band model of the density of states for the bcc transition metals is constructed. It agrees well with our isochromats and with published calculations of the density of states for Tungsten. Other electronic properties also fit well into this model. In connection with the interpretation of our isochromats a short discussion of precision experiments for the evaluation ofh/e is added.     

Quantum theory of radiation-pressure induced electrical currents: I. Free electrons

The maximum superconducting transition temperatures,T _c , of noncrystalline (Ti, Zr and Hf)-(3d metal) alloys are reported. The alloys have been produced by low temperature implantation of the 3d metals. The systematic behavior ofT _c as a function of 3d element content is discussed in comparison with metallic glasses and vapor-quenched films. A correlation between the recently observedd-band splitting in metallic glasses and superconducting behavior is pointed out.     

Spin Hall effect in Sr2RuO4 and transition metals (Nb,Ta)

We study the intrinsic spin Hall conductivity (SHC) and the d-orbital Hall conductivity (OHC) in metallic d-electron systems based on the multiorbital tight-binding model. The obtained Hall conductivities are much larger than that in p-type semiconductors. The origin of these huge Hall effects is the “effective Aharonov-Bohm phase” induced by the signs of inter-orbital hopping integrals as well as atomic spin-orbit interaction. Huge SHC and OHC due to this mechanism is ubiquitous in multiorbital transition metals.     

Electronic structure of transition metal monoantimonides: Analogy to the transition metals

A simple metallic band model is proposed for the transition metal monoantimonides, by analogy to the transition metals. It is assumed that the metal 3d electrons are itinerant in narrow bands which energetically overlap broader antimony 5p-derived bands, and the Fermi level lies in the overlap region. Consistency of the model with available data is assessed and found to be quite good.     

Zur Zustandsdichte der Übergangsmetalle

X-ray bremsstrahlung isochromats of the hcp metals Sc, Ti, Y, Zr, Lu, Hf and of the fcc metals La, Ce have been measured with high resolution under comparable conditions. The isochromats show, that the width of the conduction band (d-band) grows from the 3d-to the 5d-row of the periodic table; within each row a rigid-band-model seems to be valid. In the 5d-row only Lu fits well into this general trend of the transition metals: an X-ray spectroscopic argument, that Lu, but not La, should be placed below Sc and Y in the periodic table. Long range, low frequency spin fluctuations, which appear in Sc, Y, Lu, are not visible in the observed isochromat curves.     

A simple analytical EAM model for bcc metals including Cr and its application

An analytical embedded atom method (EAM) model, which can treat bcc transition metal Chromium, has been developed. In this model, a new potential was presented, and a modified term has been introduced to fit the negative Cauchy pressure P _c=(C₁₂-C₄₄)/2 for element Cr. The new model was applied to calculating the thermodynamic properties of binary alloys of all bcc transition metals V, Nb, Ta, Cr, Mo, W and Fe. The calculated dilute-solution enthalpies and formation enthalpies of random alloys are in good agreement with the experimental data available, the results from the first-principles calculations, and the results of thermodynamic calculations.     

Theory for superconductivity in amorphous transition metals

A theory is presented for superconductivity in amorphous transition metals. It is shown that in contrast to simple metals for transition metals the changes in the phonon spectrum, in the electronic density of states and in the electronic matrix elements which result from strong lattice disorder can enhance as well as decreaseT _c. The numerical results for the superconducting transition temperatureT _c of amorphous 4d-and 5d-transition metals agree well with the experimental results.     

Hyperfine interactions of the β-emitter12B in bcc crystals

The location of¹²B in bcc V and Ta crystals following implantation is determined by use of NMR detection and asymmetric β-decay. The expansion in the immediate surrounding of V is Δa/a=(21?4) %. Magnetic hyperfine interactions of¹²B in bcc Fe are also discussed, as the parameters regarding the location and expansion as inferred from the results on nonmagnetic bcc metals.     

Hyperfine interactions in intermetallic compounds between Gd and 3d transition metals

Measurements of hyperfine interactions at ¹⁵⁵Gd nuclei in metallic compounds between Gd and 3d transition metals and at ⁶¹Ni in GdNi compounds by Mössbauer spectroscopy are reported. The results are discussed in terms of various models proposed for the electronic structure of these compounds. The Gd isomer shifts with respect to metallic Gd are at variance with the model of a strong d electron transfer from rare earths to transition metal ions. From the observation of a linear relation between magnetic hyperfine fields at Gd and at Dy nuclei in corresponding compounds it is inferred that crystal-field induced variations of Dy moments are neglible and that the conduction electron polarization induced by 4f moments is directly related to that caused by 3d moments.     

Calculated elastic constants of dilute alloys based on bcc metals

The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for a number of dilute alloys based on Mo, Nb, W, Ta and V.     

The theory of the sound attenuation in one-dimensional metals

The elasticity theory equations are obtained for a 1d conductor. The frequency dependence of the sound attenuation is analysed, the spatial dispersion being strong or weak. The effect of oscillations of the attenuation is predicted which is due to a jumping nature of electronic motion in a non-uniform field of the sound wave, with a fixed jumping length. That is why the oscillations are of the geometric resonance type. Because of absence of Landau's damping, the frequency dependence of attenuation in a region of strong spatial dispersion is quadratic rather than linear one, as in 3d metals. This dependence is determined by a quantum nature of electronic scattering on separate impurities which move with an oscillating lattice.     

The effective ion-ion interaction of heavy alkali metals

The effective ion-ion interaction for the heavy alkali metals is calculated by a full non-local model potential, including exchange and correlation in the screening according to Vashishta and Singwi and in the RPA. The inclusion of the s-d hybridization effects merely following Harrison's theory for transition metals turns out to be inadequate for these metals.     

Compton profile study of α-manganese

The results of a Compton profile study on polycrystallineα-Mn are reported. Our measurement are compared with theoretical results computed for different 3d-4s electron configurations within the RFA model. Best agreement between the measured and calculated values is found for 3d ^5·44s ^1·6 configuration. Theoretical Compton profile ofγ-Mn calculated using the same procedure is close to that for bcc phase with similar electron configurations.     

Generalized roughening transition and its effect on the string tension

The well-understood roughening transition of an interface in the d = 3 Ising model implies an essential singularity in the string tension of the dual Z₂ gauge model. The roughening transition corresponds to the delocalization of the string due to strong long-wavelength fluctuations, and this reformulation can be generalized to other gauge groups and to d = 4 also. It is not a deconfining transition - it is expected to occur deep in the confining region - but its presence would raise serious questions about the continuation of strong coupling expansions of the tension beyond this point. In this paper predictions on the roughening transition are confronted with the available information on the string tension for different gauge groups in three dimensions.