Preparation, thermal stability and electrical transport properties of vaesite, NiS2

Vaesite, a nickel chalcogenide with NiS2 formula, has been synthetized and studied by theoretical and experimental methods. NiS2 was prepared by solid-state reaction under vacuum and densified by hot-pressing, at different consolidation conditions. Dense single-phase pellets (relative densities >94%) were obtained, without significant lattice distortions for different hot-pressing conditions. The thermal stability of NiS2 was studied by thermogravimetric analysis. Both as-synthetized and hot-pressed NiS2 have a single phase nature, although some hot-pressed samples had traces of the sulfur deficient phase, Ni1-xS (<1%vol), due to the strong desulfurization at T > 340 °C. The electronic band structure and density of states were calculated by Density Functional Theory (DFT), indicating a metallic behavior. However, the electronic transport measurements showed p-type semiconductivity for bulk NiS2, verifying its characteristic behavior has a Mott insulator. The consolidation conditions strongly influence the electronic properties, with the best room-temperature Seebeck coefficient, electrical resistivity and power factor being 182 µVK−1, 2,257 µΩ m and 14.1 µWK−2 m−1, respectively, pointing this compound as a good starting point for a new family of thermoelectric materials.

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Preparation, thermal stability and electrical transport properties of vaesite, NiS2

10.7287/peerj.preprints.27825v1 ◽

2019 ◽

Author(s):

Helena M Ferreira ◽

Elsa B Lopes ◽

José F Malta ◽

Luís M Ferreira ◽

Maria H Casimiro ◽

...

Keyword(s):

Thermal Stability ◽

Electrical Transport ◽

Hot Pressing ◽

Density Functional ◽

Single Phase ◽

Electronic Band Structure ◽

Electrical Transport Properties ◽

Electronic Band ◽

Metallic Behavior ◽

Starting Point

Vaesite, a nickel chalcogenide with NiS2 formula, has been synthetized and studied by theoretical and experimental methods. NiS2 was prepared by solid-state reaction under vacuum and densified by hot-pressing, at different consolidation conditions. Dense single-phase pellets (relative densities >94%) were obtained, without significant lattice distortions for different hot-pressing conditions. The thermal stability of NiS2 was studied by thermogravimetric analysis. Both as-synthetized and hot-pressed NiS2 have a single phase nature, although some hot-pressed samples had traces of the sulfur deficient phase, Ni1-xS (<1%vol), due to the strong desulfurization at T > 340ºC. The electronic band structure and density of states were calculated by Density Functional Theory (DFT), indicating a metallic behavior. However, the electronic transport measurements showed p-type semiconductivity for bulk NiS2, verifying its characteristic behavior has a Mott insulator. The consolidation conditions strongly influence the electronic properties, with the best room-temperature Seebeck coefficient, electrical resistivity and power factor being 182µVK-1, 2257μΩm and 14.1µWK-2m-1, respectively, pointing this compound as a good starting point for a new family of thermoelectric materials.

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Computational Analysis of Strain Effects on Electrical Transport Properties of Crystalline Nanocomposite Thin Films

Volume 11: Nano and Micro Materials, Devices and Systems; Microsystems Integration ◽

10.1115/imece2011-64641 ◽

2011 ◽

Author(s):

Hua Li ◽

Gang Li

Keyword(s):

Thin Films ◽

Electrical Conductivity ◽

Band Structure ◽

Transport Properties ◽

Electrical Transport ◽

Electronic Band Structure ◽

Electrical Transport Properties ◽

Electronic Band ◽

Strain Effects ◽

Nanocomposite Thin Films

In this work, we model the strain effects on the electrical transport properties of Si/Ge nanocomposite thin films. We utilize a two-band k·p theory to calculate the variation of the electronic band structure as a function of externally applied strains. By using the modified electronic band structure, electrical conductivity of the Si/Ge nanocomposites is calculated through a self-consistent electron transport analysis, where a nonequilibrium Green’s function (NEGF) is coupled with the Poisson equation. The results show that both the tensile uniaxial and biaxial strains increase the electrical conductivity of Si/Ge nanocomposite. The effects are more evident in the biaxial strain cases.

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Ab-initio prediction of structural, electronic and magnetic properties of Hexafluoromanganete(IV) complexes

International Journal of Modern Physics B ◽

10.1142/s0217979218502703 ◽

2018 ◽

Vol 32 (24) ◽

pp. 1850270 ◽

Cited By ~ 6

Author(s):

M. Faizan ◽

S. H. Khan ◽

A. Khan ◽

A. Laref ◽

G. Murtaza

Keyword(s):

Ab Initio ◽

Density Functional ◽

Correlation Energy ◽

Electronic Band Structure ◽

Wide Bandgap ◽

Energy Bands ◽

Electronic Band ◽

Metallic Behavior ◽

Half Metallic ◽

Exchange Correlation

In this work, detailed electronic structure calculations of alkali metal fluorides A2MnF6 (A = K, Rb, Cs) have been performed using ab-initio calculating techniques based on density functional theory (DFT). We applied different exchange correlation functionals, namely Wu–Cohen generalized gradient approximation (WC-GGA), modified Becke Johnson potential (mBJ) and GGA plus Hubbard U method in order to treat the exchange correlation energy. The calculated lattice constants are found in excellent agreement with earlier experimental results. The electronic band structure and density of states show that Cs2MnF6 is half metallic, exhibiting semiconductivity in spin up direction and metallic behavior in spin down direction. The compounds, K2MnF6 and Rb2MnF6, are predicted as wide bandgap materials. The DFT + U method gives quite accurate results of the electronic bandgap as compared with other approximations. The states Mn-3d and F-2p contribute largely to the conduction and valence energy bands. Additionally, magnetic calculations reveal strong ferromagnetic nature of these compounds. The half-metallic nature along with ferromagnetism make Cs2MnF6 a promising candidate for future applications in spintronics. Furthermore, the wide bandgap observed in K2MnF6 and Rb2MnF6 indicate their utility for light-emitting diodes (LEDs) transparent lenses and optical coatings.

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Ni-rich Nitrides ANNi3 (A = Pt, Ag, Pd) in Comparison with Superconducting ZnNNi3

Journal of Scientific Research ◽

10.3329/jsr.v4i1.9026 ◽

2011 ◽

Vol 4 (1) ◽

pp. 1 ◽

Cited By ~ 21

Author(s):

M. A. Ali ◽

A. K. M. A. Islam ◽

M. S. Ali

Keyword(s):

Optical Properties ◽

Density Functional ◽

Electronic Band Structure ◽

Generalized Gradient ◽

Band Structures ◽

Electronic Band ◽

Metallic Behavior ◽

Reflectivity Spectra ◽

Densities Of States ◽

Parameter Values

This article reports on the elastic, electronic and optical properties of predicted Ni-rich nitrides ANNi3 (A= Pt, Ag, Pd) in comparison with isostructural superconducting counterpart ZnNNi3. We have used first-principles density functional theory (DFT) with generalized gradient approximation (GGA). The independent elastic constants (C11, C12, and C44), bulk modulus B, compressibility K, shear modulus G, and Poisson’s ratio υ, as well as the band structures, total and partial densities of states and finally the optical properties of ANNi3 have been calculated. The results are then analyzed and compared with those of the superconducting ZnNNi3. The electronic band structures of the three compounds show metallic behavior with a high density of states at the Fermi level in which Ni 3d states dominate just like the superconducting ZnNNi3. Analysis of Tc expression using available parameter values suggests that the three compounds are less likely to be superconductors. Optical reflectivity spectra indicate that all the compounds have the potential to be used as a coating to remove solar heating.Keywords: ANNi3; Ab initio calculations; Elastic properties; Electronic band structure; Optical properties.© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v4i1.9026J. Sci. Res. 4 (1), 1-10 (2012)

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A Rare Low Spin Co(IV) Bis-Silyldiamide with High Thermal Stability: Exploring the Origin of an Unusual S = 1/2 Configuration

10.26434/chemrxiv.11691825.v2 ◽

2020 ◽

Author(s):

David Zanders ◽

Goran Bačić ◽

Dominique Leckie ◽

Oluwadamilola Odegbesan ◽

Jeremy M. Rawson ◽

...

Keyword(s):

Thermal Stability ◽

Density Functional ◽

Atomic Layer ◽

Epr Spectrum ◽

Functional Theory ◽

Cluster Calculations ◽

Layer Deposition ◽

Starting Point ◽

Higher Spin ◽

Surface Saturation

Attempted preparation of a chelated Co(II) β-silylamide re-sulted in the unprecedented disproportionation to Co(0) and a spirocyclic cobalt(IV) bis(β-silyldiamide): [Co[(NtBu)2SiMe2]2] (1). Compound 1 exhibits a room temperature magnetic moment of 1.8 B.M and a solid state axial EPR spectrum diagnostic of a rare S = 1/2 configuration. Semicanonical coupled-cluster calculations (DLPNO-CCSD(T)) revealed the doublet state was clearly preferred (–27 kcal/mol) over higher spin configurations for which density functional theory (DFT) showed no energetic preference. Unlike other Co(IV) complexes, 1 had remarkable thermal stability, and was demonstrated to form a stable self-limiting monolayer in initial atomic layer deposition (ALD) surface saturation tests. The ease of synthesis and high-stability make 1 an attractive starting point to begin investigating otherwise inaccessible Co(IV) intermediates and synthesizing new materials.

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Ab initio calculation on the Optical Properties of AA- Stacked two dimensional Graphene, Silicene, Germanene, and Stanene

International Journal of Computational Physics Series ◽

10.29167/a1i1p46-50 ◽

2018 ◽

Vol 1 (1) ◽

pp. 46-50

Author(s):

Rita John ◽

Benita Merlin

Keyword(s):

Optical Properties ◽

Band Structure ◽

Density Functional ◽

Electronic Band Structure ◽

Complex Refractive Index ◽

Single Layer ◽

Generalized Gradient ◽

Electronic Band ◽

Wide Range ◽

Optical Region

In this study, we have analyzed the electronic band structure and optical properties of AA-stacked bilayer graphene and its 2D analogues and compared the results with single layers. The calculations have been done using Density Functional Theory with Generalized Gradient Approximation as exchange correlation potential as in CASTEP. The study on electronic band structure shows the splitting of valence and conduction bands. A band gap of 0.342eV in graphene and an infinitesimally small gap in other 2D materials are generated. Similar to a single layer, AA-stacked bilayer materials also exhibit excellent optical properties throughout the optical region from infrared to ultraviolet. Optical properties are studied along both parallel (||) and perpendicular ( ) polarization directions. The complex dielectric function (ε) and the complex refractive index (N) are calculated. The calculated values of ε and N enable us to analyze optical absorption, reflectivity, conductivity, and the electron loss function. Inferences from the study of optical properties are presented. In general the optical properties are found to be enhanced compared to its corresponding single layer. The further study brings out greater inferences towards their direct application in the optical industry through a wide range of the optical spectrum.

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First principles calculation of structural, electronic and optical properties of (001) and (110) growth axis (InN)/(GaN)n superlattices

Revista Mexicana de Física ◽

10.31349/revmexfis.67.7 ◽

2021 ◽

Vol 67 (1 Jan-Feb) ◽

pp. 7

Author(s):

B. Bachir Bouiadjra ◽

N. Mehnane ◽

N. Oukli

Keyword(s):

Optical Properties ◽

Density Functional ◽

Electronic Band Structure ◽

Scale Up ◽

Energy Scale ◽

First Principles Calculation ◽

Full Potential ◽

Electronic Band ◽

Electronic And Optical Properties ◽

Growth Axis

Based on the full potential linear muffin-tin orbitals (FPLMTO) calculation within density functional theory, we systematically investigate the electronic and optical properties of (100) and (110)-oriented (InN)/(GaN)n zinc-blende superlattice with one InN monolayer and with different numbers of GaN monolayers. Specifically, the electronic band structure calculations and their related features, like the absorption coefficient and refractive index of these systems are computed over a wide photon energy scale up to 20 eV. The effect of periodicity layer numbers n on the band gaps and the optical activity of (InN)/(GaN)n SLs in the both growth axis (001) and (110) are examined and compared. Because of prospective optical aspects of (InN)/(GaN)n such as light-emitting applications, this theoretical study can help the experimental measurements.

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Research on Molecular Structure and Electronic Properties of Ln3+ (Ce3+, Tb3+, Pr3+)/Li+ and Eu2+ Co-Doped Sr2Si5N8 via DFT Calculation

Molecules ◽

10.3390/molecules26071849 ◽

2021 ◽

Vol 26 (7) ◽

pp. 1849

Author(s):

Ziqian Yin ◽

Meijuan Li ◽

Jianwen Zhang ◽

Qiang Shen

Keyword(s):

Molecular Structure ◽

Energy Level ◽

Density Functional ◽

Formation Energy ◽

Electronic Band Structure ◽

Blue Shift ◽

Lanthanide Ions ◽

Partial Replacement ◽

Electronic Band ◽

Charge Imbalance

We use density functional theory (DFT) to study the molecular structure and electronic band structure of Sr2Si5N8:Eu2+ doped with trivalent lanthanides (Ln3+ = Ce3+, Tb3+, Pr3+). Li+ was used as a charge compensator for the charge imbalance caused by the partial replacement of Sr2+ by Ln3+. The doping of Ln lanthanide atom causes the structure of Sr2Si5N8 lattice to shrink due to the smaller atomic radius of Ln3+ and Li+ compared to Sr2+. The doped structure’s formation energy indicates that the formation energy of Li+, which is used to compensate for the charge imbalance, is the lowest when the Sr2 site is doped. Thus, a suitable Li+ doping site for double-doped lanthanide ions can be provided. In Sr2Si5N8:Eu2+, the doped Ce3+ can occupy partly the site of Sr12+ ([SrN8]), while Eu2+ accounts for Sr12+ and Sr22+ ([SrN10]). When the Pr3+ ion is selected as the dopant in Sr2Si5N8:Eu2+, Pr3+ and Eu2+ would replace Sr22+ simultaneously. In this theoretical model, the replacement of Sr2+ by Tb3+ cannot exist reasonably. For the electronic structure, the energy level of Sr2Si5N8:Eu2+/Li+ doped with Ce3+ and Pr3+ appears at the bottom of the conduction band or in the forbidden band, which reduces the energy bandgap of Sr2Si5N8. We use DFT+U to adjust the lanthanide ion 4f energy level. The adjusted 4f-CBM of CeSr1LiSr1-Sr2Si5N8 is from 2.42 to 2.85 eV. The energy range of 4f-CBM in PrSr1LiSr1-Sr2Si5N8 is 2.75–2.99 eV and its peak is 2.90 eV; the addition of Ce3+ in EuSr1CeSr1LiSr1 made the 4f energy level of Eu2+ blue shift. The addition of Pr3+ in EuSr2PrSr2LiSr1 makes part of the Eu2+ 4f energy level blue shift. Eu2+ 4f energy level in EuSr2CeSr1LiSr1 is not in the forbidden band, so Eu2+ is not used as the emission center.

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