Lattice dynamics of CdGeP2

The bond parameters for the nearest neighbors have been determined along with the ion charges for CdGeP₂ on the basis of infrared reflection; the Cd-P and Ge-P bond matrices are similar to those for InP and GaP. The ion charges agree with those calculated from the dielectric theory. The lattice-vibration spectrum has been calculated in the long-wave limit for directions of high symmetry. The nonanalytic behavior of the frequency in the long-wave limit has also been examined. The oscillator strengths have been calculated for the optically active frequencies, and the components of the tensor for the static dielectric constant agree well with experiment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 109–113, June, 1976.We are indebted to Dr. Bettini for making available his results before publication.     

Lattice dynamics of ferromagnetic superconductor UGe2

This paper reports the lattice dynamical study of the UGe₂ using a lattice dynamical model theory based on pairwise interactions under the framework of the shell model. The calculated phonon dispersion curves and phonon density of states are in good agreement with the measured data.      

The semiconductor-to-ferromagnetic-metal transition in FeSb2

We propose FeSb₂ to be a nearly ferromagnetic small gap semiconductor, hence a direct analog of FeSi. We find that despite different compositions and crystal structures, in the local density approximation with on-site Coulomb repulsion correction (LDA+U) method magnetic and semiconducting solutions for U=2.6 eV are energetically degenerate similar to the case of FeSi. For both FeSb₂ and FeSi (FeSi_1-xGe_x alloys) the underlying transition mechanism allows one to switch from a small gap semiconductor to a ferromagnetic metal with magnetic moment ≈1 μ_B per Fe ion with external magnetic field.     

Lattice dynamics of tetragonal Nd2BaZnO5

A short‐range force constant model (SRFCM) has been applied to investigate the Raman and the infrared wavenumbers in Nd₂BaZnO₅ in its tetragonal phase of space group I4/mcm. Calculations of zone‐center phonons are made with five stretching and five bending force constants. All the Raman and infrared values are then assigned to their corresponding modes. Two Raman modes are reassigned on the basis of group theoretical calculations. The calculated Raman wavenumbers exhibit good agreement with the observed values. Copyright © 2007 John Wiley & Sons, Ltd.     

Lattice dynamics of thorium

In the present work, a local model pseudopotential has been proposed to study the lattice dynamics of thorium. The model potential depends on the core and ionic radii, and accounts for the s-d-f hybridization effects in a phenomenological way. When this form of potential is applied to derive the phonon dispersion curves of Th, sufficiently good agreement is found between the computed and experimental results.     

Lattice dynamics of SrO

The phonon dispersion relations in SrO at 300 K have been calculated along the three high symmetry directions, using a recently modified three body force shell model. Both Sr²⁺ and O^2? ions are assumed polarizable. The results show a satisfactory agreement with the neutron inelastic scattering measurements.     

Lattice dynamics of MnO

A deformation dipole model for Lattice dynamics of MnO has been formulated. Phonon dispersion curves calculated are in reasonably good agreement with experimental data. One phonon density of states of MnO is also reported.     

Lattice dynamics of beryllium

Phonon frequencies in beryllium along the principal symmetry directions have been determined by means of the slow neutron inelastic scattering technique. The data are analysed in terms of a six-neighbour force constant model and the force constants are evaluated. It is concluded that strong tensor forces are present in beryllium and the importance of this finding to basic theories of lattice dynamics is pointed out.     

Lattice dynamics of silver

The phonon dispersion curves of silver have been measured in the main symmetry directions at room temperature by coherent inelastic scattering of thermal neutrons using a correlation technique. The experimental results have been analyzed with parametrized expressions which have been derived from interatomic model potentials. With the Born-von Karman force constant model thermodynamic properties of silver could be calculated in good agreement with experimental results. Through the use of electron-ion model potentials the lattice dynamics of silver was correlated with its electronic properties. The results for some of those properties are compared with corresponding experimental values.     

Lattice dynamics of ZnO

Some phonon dispersion curves in ZnO have been determined by inelastic neutron scattering. Shell model calculations with 10 parameters were fitted to the neutron data, to optical frequencies and to dielectric constants. Good agreement was obtained including some elastic constants which were calculated from the model.     

Evidence of magnetic ordering in tellurium substituted FeSb2

We report on a⁵⁷Fe Mössbauer study of tellurium substituted FeSb₂, FeSb_2?x Tc _x (x=0.2, 0.4, 0.6), at temperatures between 4.2 K and 300 K. For all three alloys, the Mössbauer spectra at 4.2 K are characteristic of a magnetically ordered state. The hyperfine field at Fe site increases with increasing tellurium concentration. The magnetic character may be attributed to the existence of a very narrow band gap leading to fairly strong Coulomb and exchange interactions between holes in the valence band and electrons in the conduction band.     

Lattice dynamics,thermodynamic and elastic properties of CdGeAs2

Summary An extended Keating’s model with two-bond-stretching and one-angle-bending force constants within the rigid-ion approximation is applied to the investigation of the lattice dynamics of CdGeAs₂. Five model parameters of the theory are determined by a least-square fitting to the infrared reflectivity measurements. The phonon spectrum along two high-symmetry directions and the one-phonon density of states are calculated. The theoretical values of the elastic constants, the constant-volume specific heat and the Debye temperature show a reasonable agreement with the experimental data reported by other authors.     

Lattice dynamics in RbCN

The dispersion of acoustic and optical phonons of rubidium cyanide has been measured at 300 K. The acoustic branches are affected by rotation-translation coupling in a way similar to the findings in KCN. The data are explained by a model which combines a shell model and rotation-translation coupling.     

Lattice dynamics of PbxCd1-xF2 mixed superionic crystals

A modified rigid ion model has been used to investigate the one-mode behaviour in the Pb_xCd_1-xF₂ mixed crystals. It has been found that the said correlation between ionic transport properties and the flourine-cation interaction coefficient for Pb_xCd_1-xF₂ crystals is not reasonable. The agreement obtained for the zone centre frequencies with the experiment is satisfactory for all composition range.     

Lattice dynamics of sapphire (Al2O3)

Using inelastic neutron scattering we have determined all the dispersion branches of the ₁, ₂ and ₃ representations along the three-fold axis as well as the 2 times 15 branches of ₁ and ₂ symmetry along the -A-direction plus some branches along the -D-direction. The experimental data are analyzed using various rigid ion, polarizable ion and shell models. The shell models give a very satisfactory account of the dispersion curves as well as the scattering intensities. Special attention is given to the investigation of dielectric constants and equilibrium conditions.     

Lattice dynamics of ZnGeP2 and AgGaS2 in a tensor-charge model

A tensor-charge model is developed for the lattice dynamics of the ternary compounds A²B⁴C ₂ ⁵ and A¹B³C ₂ ⁶ . The long-wavelength phonon frequencies are calculated for ZnGeP₂ and AgGaS₂ crystals. The tensor-charge parameters are determined by comparing the theoretical and experimental values of the infrared intensities of active frequencies. In the crystal ZnGeP₂, the tensor charges of the zinc and phosphorus are found to be close to the isotropic charges of the point-ion model, while the tensor charge of germanium is very different from the point-ion charge. In the AgGaS₂ crystal, the tensor charges of all the atoms differ appreciably from the point-ion charges. The results are discussed from the point of view of the chemical bond.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 40–44, September, 1980.