Electronic structures (total and partial densities of states and energy bands) of Th–B systems (ThB
4
, ThB
6
, and ThB
12
structures) are determined by ab initio methods of the band theory with the ...account of relativistic effects within the spin-orbit coupling formalism and the gradient approximation of the exchange-correlation functional. Parameters of chemical bonding (orbital populations and atomic charges by Bader, Mulliken, and Löwdin) in these compounds are determined. The crystal orbital population is analyzed by the COHP method. The behavior of formation energy of these compounds is considered depending on the partial content of boron. The obtained theoretical results are compared with the previously reported data.
The crystalline and electronic band structures, thermodynamic stability, oxygen non-stoichiometry and high-temperature transport properties of perovskite-like solid solutions with a general formula ...Sr1−yFe0.5−xTa0.5+xO3−δ, where x, y ≥ 0, are thoroughly studied using a combination of experimental and theoretical methods. It is argued that the basic compound SrFe0.5Ta0.5O3−δ possesses an orthorhombic lattice symmetry, while its tantalum-doped derivatives belong to a tetragonal space group. Importantly, the purposeful addition of a certain deficiency in a strontium sublattice is shown to be a valid method for stabilizing the Sr1−yFe0.5−xTa0.5+xO3−δ oxides with an excess tantalum content. Detailed studies of charge states in an iron sublattice suggest the predominance of Fe3+ ions even in tantalum-enriched materials. Also, the band structure calculations support the semiconducting nature of electrical transport with localized n-type conductivity provided by small polarons represented by Fe2+ ions. The overall defect structure of Sr1−yFe0.5−xTa0.5+xO3−δ compounds is proved to heavily rely on oxygen vacancy (VO) formation processes; in turn, the presence of strontium vacancies is shown to be an important factor that can decrease the respective energy penalties to introduce VO defects in the lattice. As a result, the experimentally measured oxygen non-stoichiometry for Sr0.95Fe0.45Ta0.55O3−δ at elevated temperatures appears to be sufficiently enlarged as compared to pristine SrFe0.5Ta0.5O3−δ. Similar to that, the conductive properties of tantalum-enriched phase Sr0.95Fe0.45Ta0.55O3−δ are shown to be improved. On the basis of the obtained results, it is argued that cation non-stoichiometry is a valuable tool for enhancing thermodynamic and transport characteristics of perovskite-like compounds, which are currently viewed as promising materials for high-temperature applications.
The full-potential linearized augmented plane wave method with a generalized gradient approximation for the exchange-correlation potential has been applied to predict the elastic properties of ...quaternary oxypnictides LaOFe
Pn (
Pn
=
As and P) as the basic phases for the newly discovered 26–52
K superconductors. The optimized lattice parameters, independent elastic constants (
C
ij
), bulk moduli, compressibility and shear moduli are evaluated and discussed. Numerical estimates of the elastic parameters of the polycrystalline LaOFe
Pn ceramics are performed for the first time.
A comparative analysis of the electronic structure obtained in the DFT/LDA and LDA + DMFT approaches of the possible isostructural analogues of iron superconductors InCo
2
As
2
and KInCo
4
As
4
with ...the electronic structure of the parent high-temperature superconductor system BaFe
2
As
2
is carried out. It is established that in spite of the rather large value of the electron-electron correlations (local Coulomb interaction on the Co-
shell
eV, the Hund exchange interaction
eV), in the considered systems a relatively small quasiparticle mass renormalization 1.2–1.35 at the Fermi level is observed. The correlation effects lead to the remarkable shift and compression of the spectrum below –0.8 eV. The band structure of InCo
2
As
2
near the Fermi level is qualitatively similar to the previously studied BaCo
2
As
2
, and differs significantly from the band structure of BaFe
2
As
2
. In the KInCo
4
As
4
system, the bands near the Fermi level resemble the band structure of BaFe
2
As
2
, and the Fermi surfaces have a similar topology. This indirectly points to the possibility of superconductivity in KInCo
4
As
4
. Also according to the results of LDA + DMFT calculations it is seen that with a rather small hole or electron doping in the KInCo
4
As
4
system will experience topological Lifshitz transitions. We believe that the synthesis of the InCo
2
As
2
and KInCo
4
As
4
compounds considered in this paper is important for the study of superconductivity in this class of materials.
Recently it was claimed that nitrogen-doped lutetium hydride exhibited a near-ambient superconducting transition with a temperature of 294 K at a pressure of only 10 kbar, this pressure being several ...orders of magnitude lower than previously demonstrated for hydrides under pressure. In this paper, we investigate within DFT + U the electronic structure of both parent lutetium hydride LuH
3
and nitrogen doped lutetium hydride LuH
2.75
N
0.25
. We calculated corresponding bands, density of states and Fermi surfaces with and without spin-orbit coupling (SOC). It is shown that in the stoichiometric system the Lu-5
states cross the Fermi level while the H-
states make almost no contribution at the Fermi level. However, with nitrogen doping, the N‑
states enter the Fermi level in large quantities and bring together a significant contribution from the H‑
states. The presence of N-
and H-
states at the Fermi level in a doped compound can facilitate the emergence of superconductivity. Surprisingly, SOC splits quite significantly (0.1–0.25 eV) nitrogen bands in LuH
2.75
N
0.25
just below the Fermi level. For instance, nitrogen doping almost doubles the value of DOS at the Fermi level. Simple BCS analysis shows that the nitrogen doping of LuH
3
can provide
more than 100 K and even increase it with further hole doping.
Ab initio calculations were used to study the properties of a series of hexagonal (Fe
2
N-like) subcarbides M
2
C, where M = Tc, Ru, Rh, Pd, Re, Os, Ir, and Pt, and to calculate their equilibrium ...structural parameters, electronic properties, phase stability, elastic constants, compression modulus, shear modulus, Young’s modulus, compressibility, Pugh’s indicator, Poisson ratio, elastic anisotropy indices, and also hardness, Debye temperature, sound velocity, and low-temperature heat capacity. It is found based on these results that all the subcarbides are mechanically stable; however, their formation energies
E
form
are positive with respect to a mixture of
d
-metal and graphite. In addition, the calculation of the phonon spectra of these subcarbides shows the existence of negative modes, which indicates their dynamical instability. Thus, a successful synthesis of these subcarbides at normal conditions is highly improbable.
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•α and β polymorphs of BaZn2As2 as a parent phase of the new DMSs are examined.•Structural, elastic, electronic properties are evaluated from first principles.•Inter-atomic bonding ...picture is discussed.
Very recently, on the example of hole- and spin-doped BaZn2As2, quite an unexpected area of potential applications of 122-like phases was proposed as a promising platform for searching the new diluted magnetic semiconductors (DMSs) (2013; K. Zhao, et al, Nature Commun. 4:1442). Herein, by means of the first-principles calculations, we have examined in detail the basic structural, elastic, electronic properties and the peculiarities of the inter-atomic bonding in α and β polymorphs of 122-like BaZn2As2 – a parent phase of the new DMSs.
Our characterization of these materials covers the optimized structural parameters, the main elastic parameters (elastic constants, bulk, shear, and Young’s moduli, Poisson’s ratio, anisotropy indexes, and Pugh’s criterion), as well as electronic bands and densities of electronic states.
First-principles FLAPW-GGA calculations have been performed with the purpose to determine the peculiarities of the structural, electronic, magnetic properties and stability for a family of related η ...carbides M
3W
3C and M
6W
6C (where M=Fe and Co). The geometries of all phases were optimized and their structural parameters, theoretical density, cohesive and formation energies, total and partial densities of states, atomic magnetic moments have been obtained and analyzed in comparison with available theoretical and experimental data.
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