The band structures of superconducting MgB2 and the isostructural compounds CaGa2, AgB2, AuB2, ZrBe2, and HfBe2

This paper reports on a self-consistent, full-potential LMTO calculation of the band structure of the medium-T _c superconductor MgB₂ and of the isostructural hexagonal phases of CaGa₂, ZrBe₂, HfBe₂, AgB₂, and AuB₂. The factors responsible for the superconducting properties of magnesium diboride are considered. The results obtained are compared with previous calculations and available experimental data.     

Exciton states in CaF2, SrF2, and BaF2

We have applied the pseudopotential theory to the calculation of exciton states and binding energies for the ionic crystals CaF₂, SrF₂, and BaF₂, using a transfer model. Because of the satisfying agreement between our results and the experimental data in each case, we assume this pseudopotential formalism will describe transfer exciton states and energies in other ionic crystals.     

Linewidth and auger effect in CaF2, SrF2, and BaF2

In BaF₂ crystals, the linewidth of certain core band-conduction band excitons shows strong temperature dependence, while the corresponding linewidths in CaF₂ and SrF₂ do not. Calculations of the broadening due to the temperature-independent Auger effect are in good agreement with experimental data.     

Real-gas properties of n-alkanes, O2, N2, H2O, CO, CO2, and H2 for diesel engine operation conditions

The objective of the research outlined in this paper was to develop the analytical approximations for calculating real-gas properties (p-v-T data, thermodynamic functions: internal energy, enthalpy, and entropy, and specific heats) of vapor-phase n-alkanes from C₁ (methane) to C₁₄ (normal tetradecane), O₂, N₂, H₂O, CO, CO₂, and H₂ within the range of pressure 0.05 MPa ≤ p ≤ 20 MPa and temperature 280 K ≤ T ≤ 3000 K aimed for implementation into computational fluid dynamics (CFD)-codes simulating the operation process in modern Diesel engines. The analytical approximations have been developed based on available literature data and on the new equation of state for moderately dense gases. The approximations reported are rather simple and therefore can be used directly in CFD codes. Approximations for mixing rules are also provided.     

UV absorption cross section of the molecules O2, NO,N2O,CO2, H2O,and NO2

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 3, pp. 455–465, March, 1990.     

Measurement of the Kerr constant of He,A, O2, N2, H2 and D2

Summary The Kerr electro-optic constant of helium, argon and of molecular oxygen, nitrogen, hydrogen and deuterium have been measured at room temperature and low pressure, by using a low-frequency-modulated electric field. In this paper the density is given in amagat,i.e. in moles per molar volume.     

Change of hyperfine and transferred hyperfine interaction of Eu2+ in CdF2, CaF2, SrF2, and BaF2

ENDOR measurements of the hyperfine and transferred hyperfine interaction of Eu²⁺ in CdF₂, SrF₂, and BaF₂ were performed. Compared with measurements on CaF₂, there is a radial shifting of the next fluorine ligands in CdF₂∶ +5.4%, CaF₂∶ + 3.5%, and BaF₂∶ ?3.9%. Since the SrF₂ and EuF₂ lattice constants are approximately equal, a shifting in SrF₂ was not assumed. In both europium isotopes (151 and 153) a change of hyperfine fields at the nucleus was observed. This can be explained qualitatively by the difference in radial distribution of the different europium orbitals. Also noticed was a small change of the hyperfine anomaly, which indicates contributions of the zero-point vibration.     

Phonon dispersion and thermodynamical properties in ZrB2, NbB2, and MoB2

The structural and lattice dynamical calculations are performed on ZrB₂, NbB₂, and MoB₂ compounds using the first-principles of total energy calculations. Generalized gradient approximations (GGA) are used to model exchange-correlation effects. Structural results of these calculations are consistent with past experimental data and other theoretical findings. Our lattice dynamical results regarding phonon dispersion curves and temperature-dependent behavior of thermodynamical properties (entropy, heat capacity, internal energy, and free energy) contribute to the existing literature on these compounds.     

Angular distribution of the photoelectron spectrum of CO2, COS,CS2, N2O,H2O,and H2S

The photoelectron spectra of the triatomic molecules CO₂, COS, CS₂, N₂O, H₂O, and H₂S have been measured as a function of the angle θ between the direction of the incoming photon and outgoing photoelectron. The photoelectron spectra have been measured with a double-focusing electrostatic electron spectrometer to which has been attached a chamber containing a gas discharge lamp that can be freely rotated. (The photon source used was the 21.22 eV He I resonance line). From the dependence of intensity as a function of θ the angular parameter β was determined for each ionization band observed in the photoelectron spectra. A correlation was noted between the values of β and the molecular orbitals relative to the contributions of oxygen and sulfur atomic orbitals. Individual β values were also obtained for most of the vibrational bands seen in the photoelectron spectra. In most cases the vibrational structure showed little or no change in the angular parameter for a given electronic state. In certain cases, however, such as the fourth ionization band in CS₂, CO₂, and COS, rather sizeable changes in β were observed for the different vibrational bands.     

Structural,magnetic and neutron diffraction studies on TbFe2-TbAl2, TbCo2-TbAl2 and HoCo2-HoAl2

Both pseudobinary systems exhibit large homogeneous regions of cubic and hexagonal Laves phases. Ordering tendencies on crystallographic sites between Al and the transition metals are observed in the hexagonal type.Electron transfer to the transition metals quenches their moments so that they become nonmagnetic at high Al concentrations. The peculiarities in the mechanism of magnetization which appear in rare earth dialuminides when Al is replaced by a transition metal have been studied in detail at cryogenic temperatures.The first replacement of Al results in a decrease in saturation moment. Neutron diffraction verifies the low ordered rare earth sublattice moments and reveals the ‘lost part’ as a disordered component. Considerable magnetic hardness develops in certain regions of concentration often connected with spontaneous increases in magnetization with field. All available evidence suggests the presence of unusual domain wall effects to be responsible for this effect. High remanences develop in both the hexagonal and in the cubic structures in the intermediate region. The development of disordered magnetic components is connected either with the disorder on crystallographic sites or changes in the free electron concentration.     

Adsorption and solution of H2, D2, N2, O2 and CO by (100) Ta

Sticking coefficients, saturation densities, and solution rates of gases on (100) Ta are obtained by comparing with results on (100) W using Auger electron spectroscopy and flash desorption. Hydrogen has a lower sticking coefficient on (100) Ta than on polycrystalline Ta, but solution occurs readily even at 78°K. Differences between H₂ and D₂ are observed for both adsorption and solution. Nitrogen is confined to the surface of Ta for T < ≈500°K, and adsorbed nitrogen dissolves with an activation energy of ≈2.5 kcal mole^?1 upon heating to higher temperatures. The saturation density of O₂ at 300° K is approximately twice that on (100) W. The first monolayer dissolves at ≈500°K but the second dissolves or desorbs only at much higher temperatures. Carbon monoxide adsorbs without solution of either species at 300°K. At ≈500°K carbon dissolves completely leaving oxygen which desorbs at much higher temperature.     

Electron energy loss measurements on PbF2, PbCl2, PbBr2 and PbI2

The results of electron energy loss measurements on polycrystalline films of PbF₂, PbC1₂, PbBr₂ and PbI₂ are present and the calculated dielectric functions are discussed in relation to their band structures and optical data.     

Vitrification of and optical and photoelectrical properties of AgAsS2, AgSbS2, and AgBiS2

A study is made concerning the photoconductivity, the edge absorption, and the far-infrared spectra of AgAsS₂, AgSbS₂, AgBiS₂ crystals and glasses. The oscillation spectrum of monoclinic smithite (AgAsS₂) and miargyrite (AgSbS₂) is explained here by the presence of As-S, Sb-S, and Ag-S bonds. The rank of symmetry and the degree of bond metallization, which both increase in the order AgAsS₂ AgSbS₂ AgBiS₂, cause the structure of the far-infrared spectra to become simpler and the tendency vitrification to become weaker in the same order.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 39–45, March, 1976.     

Energy band structures of the chalcopyrite lattice semiconductors CuAlS2, CuAlSe2, CuInS2, and CuInSe2

The pseudopotential method is used to calculate the energy band structures of four -type semiconductors including the effect of the displacement of anions from face-centered sites in the sublattices. It was established that CuAlSe₂, CuInS₂, and CuInSe₂ are direct gap semiconductors and that CuAlS₂ has a pseudodirect energy gap. Experimental data derived from studies of the optical properties of these crystals in the U V region are also discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 7–12, June, 1976.     

Electron impact ionization cross-section of C2, C3, Si2, Si3, SiC,SiC2 and Si2C

Total ionization cross-sections for C₂, C₃, Si₂, Si₃, SiC, SiC₂ and Si₂C molecules have been calculated by electron impact. Spherical complex optical potential formalism has been employed for obtaining the inelastic cross-sections for these molecules. Then by applying complex scattering potential-ionization contribution method, total ionization cross-sections are derived. These cross-sections are calculated in the energy range from ionization threshold to 2?keV. There are no measurements available in the literature to the best of our knowledge with which our results can be compared. The results show a linear relationship between maximum ionization cross-section and square root of the ratio of polarizability to ionization potential, depending on its atomicity. This gives a confirmation for the consistency of the data reported here. Present work is a maiden attempt to find electron impact ionization cross-section for these molecules, except for C₂ and C₃.