arXiv subjects

I. R. Shein

Publications and source records attributed to I. R. Shein.

At least 55 records · Page 3Linked to original sources

arXiv2008

Band structure of (Sr3Sc2O5)Fe2As2 as a possible parent phase for new FeAs superconductors

By means of first-principles FLAPW-GGA calculations, we have investigated the electronic properties of the newly synthesized layered phase - (Sr3Sc2O5)Fe2As2. The electronic bands, density of states and Fermi surface have been evaluated. The resembling of our data for (Sr3Sc2O5)Fe2As2 with band structure pictures of known FeAs superconducting materials may be considered as the theoretical background specifying the possibility for (Sr3Sc2O5)Fe2As2 to become a parent phase for new FeAs superconductors.

cond-mat.supr-con↗

arXiv2008

Electronic and elastic properties of new nitrogen-containing perovskite-like superconductor ZnNNi3

Full-potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential has been applied for the study of structural, elastic and electronic properties of the newly synthesized nitrogen-containing perovskite-like superconductor ZnNNi3. The optimized lattice parameter, independent elastic constants (C11, C12 and C44), bulk modulus B, compressibility betta, and shear modulus G are evaluated. The band structure, total and site- projected l- decomposed DOSs, the shape of the Fermi surface, the Sommerfeld coefficient and the molar Pauli paramagnetic susceptibility for this novel anti-perovskite are obtained and analyzed in comparison with related anti-perovskites ZnCNi3 and MgCNi3

cond-mat.supr-con↗

arXiv2008

First-principles study of electronic band structure and elastic properties of superconducting nanolaminate Ti2InC

The full-potential linearized augmented plane wave method with the generalized gradient approximation for the exchange-correlation potential (FLAPW-GGA) is used to predict the electronic and elastic properties of the newly discovered superconducting nanolaminate Ti2InC. The band structure, density of states and Fermi surface features are discussed. The optimized lattice parameters, independent elastic constants, bulk and shear moduli, compressibility are evaluated and discussed. The elastic parameters of the polycrystalline Ti2InC ceramics are estimated numerically for the first time.

cond-mat.mtrl-sci↗

arXiv2008

Band structure of tetragonal and orthorhombic fluorine-arsenide SrFeAsF as a parent phases for a new group of oxygen-free FeAs superconductors

The full-potential linearized augmented plane wave method with the generalized gradient approximation for the exchange and correlation potential (LAPW-GGA) is used to understand the electronic band structure of fluorine-arsenide SrFeAsF as a possible parent material for a new group of oxygen-free FeAs superconductors. The electronic bands, density of states, Fermi surface and atomic charges have been evaluated and discussed for high-temperature tetragonal and low-temperature orthorhombic SrFeAsF phases.

cond-mat.supr-con↗

arXiv2008

Band structure of SrFeAsF and CaFeAsF as parent phases for a new group of oxygen-free FeAs superconductors

By means of first-principle FLAPW-GGA calculations, we have investigated the electronic properties of the newly discovered layered quaternary systems SrFeAsF and CaFeAsF as parent phases for a new group of oxygen-free FeAs superconductors. The electronic bands, density of states, Fermi surfaces, atomic charges, together with Sommerfeld coefficients and molar Pauli paramagnetic susceptibility have been evaluated and discussed in comparison with oxyarsenide LaFeAsO - a parent phase for a new class of high-temperature (Tc about 26-56K) oxygen-containing FeAs superconductors. Similarity of our data for SrFeAsF and CaFeAsF with the band structure of oxygen-containing FeAs superconducting materials may be considered as theoretical background specifying the possibility of superconductivity in these oxygen-free systems.

cond-mat.supr-con↗

arXiv2008

Electronic band structures and intra-atomic interactions in layered quaternary oxyarsenides LaZnAsO and YZnAsO

First-principle FLAPW-GGA band structure calculations are employed to obtain the structural, electronic properties and chemical bonding picture for two related layered phases, namely, quaternary oxyarsenides LaZnAsO and YZnAsO. These compounds are found to be direct-transition type semiconductors with the GGA gaps of about 0.65-1.30 eV. The peculiarities of chemical bonding in these phases are investigated and discussed in comparison with quaternary oxyarsenide LaFeAsO - a basic phase for the newly discovered 26-52K superconductors.

cond-mat.mtrl-sci↗

arXiv2008

Elastic properties and chemical bonding in ternary arsenide SrFe2As2 and quaternary oxyarsenide LaFeAsO - basic phases for new 38-55K superconductors

We report the first-principle FLAPW-GGA calculations of the elastic properties of two related layered phases, namely, the ternary arsenide SrFe2As2 and the quaternary oxyarsenide LaFeAsO - basic phases for the newly discovered "122" and "1111" 38-55K superconductors. The independent elastic constants (Cij), bulk moduli, compressibility, and shear moduli are evaluated and discussed. The numerical estimates of the elastic parameters of the polycrystalline SrFe2As2 and LaFeAsO ceramics are performed for the first time. Additionally, the peculiarities of chemical bonding in these phases are discussed.

cond-mat.supr-con↗

arXiv2008

Elastic properties of ternary arsenide SrFe2As2 and quaternary oxyarsenide LaOFeAs as basic phases for new 38-55K superconductors from first principles

Here we report the first-principle FLAPW-GGA calculations of the elastic properties of two related phases, namely, the ternary arsenide SrFe2As2 and the quaternary oxyarsenide LaOFeAs as the basic phases for the newly discovered "1111" and "122" 38-52K superconductors. The independent elastic constants (Cij), bulk moduli, compressibility, and shear moduli are evaluated and discussed. Additionally, numerical estimates of the elastic parameters of the polycrystalline LaOFeAs and SrFe2As2 ceramics are performed for the first time.

cond-mat.supr-con↗

arXiv2008

Electronic structure of oxygen-free 38K superconductor Ba1-xKxFe2As2 in comparison with BaFe2As2 from first principles

Based on first-principles FLAPW-GGA calculation, we have investigated electronic structure of newly discovered oxygen-free 38K superconductor Ba1-xKxFe2As2 in comparison with parent phase - tetragonal ternary iron arsenide BaFe2As2. The density of states, magnetic properties, near-Fermi bands compositions, together with Sommerfeld coefficients and molar Pauli paramagnetic susceptibility are evaluated. The results allow us to classify these systems as quasi-two-dimensional ionic metals, where the conduction is strongly anisotropic, only happening on the (Fe-As) layers. According to our calculations, at the hole doping of BaFe2As2 the density of states at the Fermi level grows, and this can be a possible factor of occurrence of superconductivity for Ba1-xKxFe2As2. On the other hand, Ba1-xKxFe2As2 lays at the border of magnetic instability and the pairing interactions might involve magnetic or orbital fluctuations.

cond-mat.supr-con↗

arXiv2008

Electronic structure of new quaternary superconductors LaONiBi and LaOCuBi from first principles

Based on first-principles FLAPW-GGA calculations, we have investigated the electronic structure of newly synthesized novel superconductors LaONiBi and LaOCuBi, the first bismuth-containing compounds from the family of quaternary oxypnictides which attract now a great deal of interest in search for novel 26-55K superconductors. The band structure, density of states and Fermi surfaces are discussed. Our results indicate that the bonding inside of the (La-O) and (Ni(Cu)-Bi) layers is covalent whereas the bonding between the (La-O) and (Ni(Cu)- Bi) blocks is mostly ionic. For both oxybismuthides, the DOSs at the Fermi level are formed mainly by the states of the (Ni(Cu)-Bi) layers, the corresponding Fermi surfaces have a twodimensional character and the conduction should be strongly anisotropic andhappen only on the (Ni(Cu)-Bi) layers. As a whole, the new oxybismuthides may be described as low-TC superconducting non-magnetic ionic metals.

cond-mat.supr-con↗

arXiv2008

Electronic structure and magnetism in BeO nanotubes induced by boron, carbon and nitrogen impurities

We have performed ab initio calculations to systematically investigate electronic properties and magnetism of insulating non-magnetic beryllium monoxide nanotubes induced by non-magnetic sp impurities: boron, carbon and nitrogen. We found that in the presence of these sp impurities, which replace oxygen atoms, the non-magnetic BeO NTs transform into magnetic semiconductors, which acquire magnetization caused by spin splitting of (B,C,N) 2p states located in the forbidden gap of a BeO tube. The magnetic moments of the impurities vary from 0.65 to 1.60. On the contrary, when (B,C,N) dopants substitute for Be atoms or in the presence of an oxygen vacancy, the nonmagnetic state of the BeO tubes is retained.

cond-mat.mtrl-sci↗

arXiv2008

Atomic models of non-stoichiometric layered diborides M$_{1-x}$B$_2$ (M = Mg, Al, Zr and Nb) from first principles

Two atomic models of non-stoichiometric metal diborides M$_{1-x}$B$_2$ are now assumed: (i) the presence of cation vacancies and (ii) the presence of 'super-stoichiometric' boron which is placed in cation vacancy site. We have performed first principle total energy calculations using the VASP-PAW method with the generalized gradient approximation (GGA) for the exchange-correlation potential in a perspective to reveal the trends of M$_{1-x}$B$_2$ possible stable atomic configurations depending on the type of M cations (M = Mg, Al, Zr or Nb) and the type of the defects (metal vacancies versus metal vacancies occupied by 'super-stoichiometric' boron in forms of single atoms, dimers B$_2$ or trimers B$_3$). Besides we have estimated the stability of these non-stoichiometric states (on the example of magnesium-boron system) as depending on the possible synthetic routes, namely via solid state reaction method, as well as in reactions between solid boron and Mg vapor; and between these reagents in gaseous phase. We demonstrate that the non-stoichiometric states such as B$_2$ and B$_3$ placed in metal sites may be stabilized, while the occupation of vacancy sites by single boron atoms is the most unfavorable.

cond-mat.mtrl-sci↗

arXiv2008

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.

cond-mat.mtrl-sci↗

arXiv2008

Elastic properties of quaternary oxyarsenide LaOFeAs as basic phase for new 26-52K superconductors

The full-potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential has been applied to predict the elastic properties of quaternary oxyarsenide LaOFeAs - the basic phase for the newly discovered 26-52K superconductors. The optimized lattice parameters, independent elastic constants (Cij), bulk modulus B, compressibility betta, and shear modulus G are evaluated and discussed. For the first time the numerical estimates of the elastic parameters for polycrystalline LaOFeAs ceramics are performed. Our analysis shows that LaOFeAs belong to the anisotropic mechanically stable systems; a parameter limiting the mechanical stability of this material is the shear modulus. In addition, LaOFeAs is a soft material (B -98 GPa) with high compressibility (betta - 0.0102 1/GPa); lays at the border of a brittle behavior and adopts a high ionic contribution in intra-atomic bonding.

cond-mat.supr-con↗

arXiv2005

First-principles study of cubic perovskites SrMO_3 (M = Ti, V, Zr and Nb)

Using the full-potential linearized-augmented-plane-wave (FLAPW) method, we have analyzed systematically the trends in the structural and electronic properties of the 3d and 4d transition-metal oxides SrMO_3 (M = Ti, V, Zr and Nb). The optimized lattice parameters, bulk modules, densities of states, band structures and charge density distributions are obtained and compared with the available theoretical and experimental data. The energy gap between O2p - Md bands increases as the covalency of the system decreases going from 3d to 4d based perovskites. The electron configurations of Sr(Ti,Zr)O_3 and Sr(V,Nb)O_3 usually referred to as d^0 and d^1 oxides, respectively, differ considerably from these idealized "ionic" configurations, and the deviations increase with increasing of the d-p covalent overlap in the oxides.

cond-mat.mtrl-sci↗

arXiv2004

Electronic structure of silver-deficient hexagonal AgB$_2$

Electronic structure and cohesive properties of metastable hexagonal AgB_{2} and silver-deficient borides Ag_{0.875}B_{2} and Ag_{0.750}B_{2} were investigated by means of the projected augmented wave method in the framework of the density functional theory (VASP package). We found that the density of states at the Fermi level for nonstoichiometric diborides is almost constant within a range of vacancy content up to 25%. The formation energy of metal vacancies in silver diboride is the least among all 4d metal diborides, i.e. for AgB_{2} is possible to expect the wide homogeneity region.

cond-mat.mtrl-sci↗

arXiv2004

Electronic band structure and chemical bonding in the novel antiperovskite ZnCNi3 as compared with 8-K superconductor MgCNi3

Energy band structure of the discovered ternary perovskite-like compound ZnCNi3 reported by Park et al (2004) as a non-superconducting paramagnetic metal was investigated using the FLMTO-GGA method. The electronic bands, density of states, Fermi surface, charge density and electron localization function distributions for ZnCNi3 are obtained and analyzed in comparison with the isoelectronic and isostructural 8K superconductor MgCNi3. The effect of external pressure on the electronic states of ZnCNi3 and MgCNi3 is studied.

cond-mat.supr-con↗

arXiv2003

Electronic band structure of novel 18-K superconductor Y2C3 as compared with YC and YC2

The electronic band structure of yttrium sesquicarbide Y2C3(Pu2C3 structural type) reported by Akimitsu et al. (2003) as a novel 18-K superconductor is investigated using the first-principle full-potential LMTO method and compared with those of yttrium mono- and dicarbide: cubic YC and 4-K superconductor YC2 (CaC2 structural type). Our results show that the enhanced Tc of Y2C3 as compared with YC2 may be interpreted by the electronic factors: the near-Fermi DOS for Y2C3 was found to be about 70% higher that for YC2, and the contribution from the C2p states increases. The Fermi level of the "ideal" bcc Y2C3 is located near the local DOS minimum, and the superconducting properties of Y2C3-based materials would be very sensitive to synthesis conditions and the presence of impurities and lattice vacancies. We suppose that by changing these factors it is possible to vary Tc for the yttrium sesquicarbide.

cond-mat.supr-con↗