Investigations on non-stoichiometric zirconium nitrides

Non-stoichiometric zirconium nitride thin films were prepared by reactive dc magnetron sputtering. Structural, optical and electrical properties were investigated with respect to nitrogen gas flow. The film characterization was obtained through various techniques: Rutherford back scattering (RBS), X-ray diffraction (XRD), reflectometry and a four probe method. We found that the deposition rate decreases while the nitrogen flow increases. Also it was shown that a stoichiometric compound (ZrN) is formed at a 4 sccm nitrogen flow. It has a rock-salt structure and presents a minimum of resistivity and a gold-like color. As nitrogen flow increases, films become more and more amorphous, semi-transparent and electrically resistive. Furthermore, at a nitrogen flow of 9 sccm, the nitrogen to zirconium atomic concentration ratio is near 1.33 and the film exhibits properties close to those of a Zr₃N₄ phase.     

Electronic structure of nitrides PuN and UN

The electronic structure of uranium and plutonium nitrides in ambient conditions and under pressure is investigated using the LDA + U + SO band method taking into account the spin–orbit coupling and the strong correlations of 5f electrons of actinoid ions. The parameters of these interactions for the equilibrium cubic structure are calculated additionally. The application of pressure reduces the magnetic moment in PuN due to predominance of the f ⁶ configuration and the jj-type coupling. An increase in the occupancy of the 5f state in UN leads to a decrease in the magnetic moment, which is also detected in the trigonal structure of the UN _x β phase (La₂O₃-type structure). The theoretical results are in good agreement with the available experimental data.     

Electronic structure of zirconium dihydride

Using linearized muffin-tin orbitals, with the atomic spheres corrected for overlap, we have performed a self-consistent calculation of the electronic structure of the cubic phase of zirconium dihydride. We have calculated the electronic structure of nonstoichiometric ZrH_1.75. We have studied the effects of a hydrogen vacancy on the electronic characteristics. Assuming a low positron density, we calculated the positron spectrum, the positron lifetime, and the contributions to electron-positron annihilation of various electronic states. We obtained a reasonably good agreement between our theoretical results and the experimental data. Institute of Strength Physics and Meterials Research, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 96–103, august, 1996.     

Electronic structure of ErH2

A band structure study reveals that in contrast to the pure rare earth metal, the Fermi level of the dihydride falls near the bottom of the 5d band, in a region of low density of states; consequences on Fermi surface geometry, magnetic properties and resistivity are suggested. Below the metal d states lie two overlapping metal-hydrogen bands, in agreement with Weaver's photoemission data and Switendick's result on YH₂.     

Electronic structure of TiH2

The electronic structure of TiH₂ has been studied using the augmented-plane-wave method and the LCAO interpolation. The density of states and its orbital components show that the conduction band is Ti d-like and that the valence band is largely derived from the hydrogen orbitals with small Ti 3d hybridization. The electronic charges on the hydrogen atom are ～ 1.5 as compared to 1.6–1.7 of the rare-earth metal hydrides.     

Ferromagnetism of non-stoichiometric UFe2 compounds

The ac magnetic susceptibility of non-stoichiometric UFe₂ Laves compounds was measured between 40 and 200 K. It was found that the transition temperature of the investigated compounds is directly proportional to the iron content.     

Electronic band structure of KTaO3

Calculations are presented for the electronic band structure of the perovskite-type crystal KTaO₃. The results are obtained using the LCAO method in a modified form. On comparison with experimental data good agreement was found after a reassignment of one transition.     

Electronic structure studies of CeAgSb2

The electronic band structure of CeAgSb₂ has been calculated using the self-consistent full potential nonorthogonal local orbital minimum basis scheme based on the density functional theory. We investigated the electronic structure with the spin-orbit interaction and on-site Coulomb potential for the Ce-derived 4f orbitals to obtain the correct ground state of CeAgSb₂.     

Electronic band structure of TiCl3

Energy bands for the 3d? electrons of Ti³⁺ in the high temperature structure of TiCl₃ have been calculated by the tight-binding approximation. Cubic symmetry around each Ti³⁺ is assumed and transfer between the 3p atomic orbitals of Cl^? and 3d? atomic orbitals of Ti³⁺ is considered. Two singlet bands and two doublet bands with no dispersion have been obtained. The dispersionless character is discussed by constructing Wannier functions.     

Electronic structure and hyperfine fields in non-stoichiometric magnetite above the Verwey transition

The NMR spectra of ⁵⁷Fe nuclei were measured below and above the Verwey transition temperature T_V in single crystal samples of Fe_3(1?δ)O₄ (0?δ?0.009). The measured crystals were grown from the melt using the cold crucible technique. In a cubic phase above T_V the satellite structure induced by vacancies in the octahedral sublattice is clearly resolved. The satellite lines originate from those iron nuclei in the tetrahedral sublattice that are nearest to the vacancy. Temperature dependence of satellite lines indicates that the presence of vacancy leads to a redistribution of the electrons in octahedral sublattice and the appearance of iron ions possessing appreciable orbital momentum.     

Magnetic structure of the cubic U2Te3 with a non-stoichiometric Th3P4 type of structure

The neutron diffraction patterns of the cubic U₂Te₃ have been obtained at 15 and 150 K. There are no extrapeaks of magnetic origin below the Curie point T_c = 70 ± 5 K. Thus the ordering corresponds to a collinear ferromagnetic structure. The value of the magnetic moment is 1.78 μ_B which is close to those values determined for a few cubic uranium pnictides and chalcogenides.     

Electronic structure and magnetism of CeCoGe3

The electronic band structure of CeCoGe₃ has been calculated using the self-consistent full potential nonorthogonal local orbital minimum basis scheme based on density functional theory. We investigated the electronic structure with the spin-orbit interaction and on-site Coulomb potential for the Ce-derived 4f orbitals to obtain the correct ground state of CeCoGe₃. The exchange interaction between local f electrons and conduction electrons play an important role in their heavy fermion characters. The fully relativistic band structure scheme shows that spin-orbit coupling splits the 4f states into two manifolds, the 4f_7/2 and the 4f_5/2 multiplets.     

Electronic structure and magnetism of FeGe2

The electronic band structure of FeGe₂ has been calculated using the self-consistent full potential non-orthogonal local orbital minimum basis scheme based on the density functional theory. In the band structure of FeSn₂, Fe 3d and Sn 5p states play important roles near the Fermi level. Our calculations show that large enhancement of the static susceptibility over its non-interacting value is found due to a peak in the density of states at the Fermi level.     

Electronic structure and equilibrium properties of hcp titanium and zirconium

The electronic structures of hexagonal-close-packed divalent titanium (3-d) and zirconium (4-d) transition metals are studied by using a non-local model potential method. From the present calculation of energy bands, Fermi energy, density of states and the electronic heat capacity of these two metals are determined and compared with the existing results in the literature.     

X-ray band spectra and electronic structure of carbides and nitrides of zirconium,niobium and molybdenium

The L- and M-emission spectra of Zr, Mb and Mo carbides and nitrides have been studied. The spectra were excited by primary techniques, it is concluded that the valence bands of these carbides and nitrides consist of two sub-bands: a sub-band of states which participate in covalent bonds and a sub-band of states which share in the formation of metallic bonding and account for the metallic properties of these phases.     

Electronic transport properties of hafnium/zirconium multilayers

We have investigated the electrical resistivity, superconducting transition temperature, and upper critical field as a function of layer thickness in hafnium/zirconium ( ) metallic superlattices. These films have equal Hf and Zr layer thicknesses (d_h and d_z, respectively). We have studied a series of samples with modulation wavelength λ = d_h + d_z ranging from 20 to 250 Å. All films show a metallic type of resistivity, with remarkably little difference in both room temperature and liquid helium resistivities. All structures undergo a transition to a superconducting state, with the transition temperature remaining nearly constant across the series. This indicates that the interface region of these structures is of rather high quality. Upper critical fields both parallel and perpendicular to the sample plane were determined. Because of the relatively large superconducting coherence length, these films behave essentially three-dimenstionally throughout the range of λ studied. However, we also observe a somewhat anomalous behavior in the ratio of the parallel to perpendicular critical fields near the transition temperature, the origin of which is not yet known.     

Electronic structure of Li3GaN2

First principles calculations, by means of the full-potential linearized augmented plane wave method within the local density approximation, were carried out for the electronic properties of Li₃GaN₂. The calculated lattice parameter is in good agreement with the measured one. The bandgap is direct at the Brillouin zone centre. The Li-N and Ga-N bonds are both ionic with a small covalent character of the latter one.     

Electronic structure of Sr2FeMoO6

We have used electron spectroscopies to investigate the electronic structure of the double perovskite Sr₂FeMoO₆. The valence-band photoemission spectra present a well-defined cut-off at the Fermi level, indicative of the metallic character of the material. The O 1s X-ray absorption spectrum presents three peaks, which are in good correspondence with the main structures in the unoccupied density-of-states of DF-LDA calculations. The electron energy-loss spectra present two structures which are also interpreted in terms of transitions between the bands obtained in the DF-LDA calculations.