12 research outputs found
Anatomy of the band structure of the newest apparent near-ambient superconductor LuHN
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 and nitrogen doped lutetium hydride LuHN. We
calculated corresponding bands, density of states and Fermi surfaces. It is
shown that in the stoichiometric system the Lu-5d states cross the Fermi level
while the H-1s states make almost no contribution at the Fermi level. However,
with nitrogen doping, the N-2p states enter the Fermi level in large quantities
and bring together a significant contribution from the H-1s states. The
presence of N-2p and H-1s states at the Fermi level in a doped compound can
facilitate the emergence of superconductivity. For instance, nitrogen doping
almost doubles the value of DOS at the Fermi level. Simple BCS analysis shows
that the nitrogen doping of LuH can provide T more than 100K and even
increase it with further hole doping.Comment: 7 pages, 5 figure
Structural, electronic properties and Fermi surface of ThCr2Si2-type charge-balanced KFe2AsSe phase as a parent system for a new group of "mixed" pnictide-chalcogenide superconductors
The ThCr2Si2-type arsenide-selenide phase KFe2AsSe is proposed as a parent
system for a new "intermediate" group of Fe-based superconducting materials
bridging the known families of Fe-pnictides (such as BaFe2As2) and
Fe-chalcogenides (such as KxFe2-ySe2) superconductors. The characterization of
the proposed charge-balanced phase by means of FLAPW-GGA approach covers the
crystal structure, As/Se atomic ordering, stability, electronic bands, Fermi
surface, and density of electronic states.Comment: 8 pages, 4 figure
Elastic properties of mono- and polycrystalline hexagonal AlB2-like diborides of s, p and d metals from first-principles calculations
We have performed accurate ab initio total energy calculations using the
full-potential linearized augmented plane wave (FP-LAPW) method with the
generalized gradient approximation (GGA) for the exchange-correlation potential
to systematically investigate elastic properties of 18 stable, meta-stable and
hypothetical hexagonal (AlB2-like) metal diborides MB2, where M = Na, Be, Mg,
Ca, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ag and Au. For monocrystalline
MB2 the optimized lattice parameters, independent elastic constants (Cij), bulk
modules (B), shear modules (G) are obtained and analyzed in comparison with the
available theoretical and experimental data. For the first time numerical
estimates of a set of elastic parameters of the polycrystalline MB2 ceramics
(in the framework of the Voigt-Reuss-Hill approximation), namely bulk and shear
modules, compressibility, Young's modules, Poisson's ratio, Lame's coefficients
are performed.Comment: 24 pages, 3 figure
Effect of Li and Li-RE co-doping on structure, stability, optical and electrical properties of bismuth magnesium niobate pyrochlore
New BiMgLixNbO (x = 0.25; 0.40) and BiREMgLiNbO (RE – Eu, Ho, Yb) compounds with the pyrochlore structure were synthesized. The displacements of the A-site atoms (96g) and O' ones (32e) as well as the Li and RE atoms distribution in the A-sites were determined. The dopant distribution was proven by ab initio calculations. The most preferable (BiLi)(NbMg)O model was predicted with a direct band gap of 3.18 eV corresponding to the experimental Eg for BiMgLiNbO. The thermal stability of the compounds in air up to 1100–1220 °C and the reducing atmosphere up to 400 °C was determined. The charge disbalance in the AO' sublattice and the oxygen vacancies predetermine the dielectric behavior of the ceramics up to 200 °C, the mixed conductivity at high temperatures (T > 200 °C), and the proton transport up to 400 °C
Photocatalytic Properties of Bi2xTi2O71.5x (x = 0, 0.5) Pyrochlores: Hybrid DFT Calculations and Experimental Study
Synthesis and characterisation of new MO(OH)2 (M = Zr, Hf) oxyhydroxides and related Li2MO3 salts
Two new solid MO(OH)2 (M = Zr, Hf) oxyhydroxides have been synthesised by an ion-exchange reaction from Li2MO3 (M = Zr, Hf) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P21/c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling