13,767 research outputs found
Elastic and electronic properties of PbO-type FeSe1-xTex (x = 0 - 1.0): A first-principles study
The effect of doping on electronic and other related properties of PbO-type
FeSe1-xTex has been investigated theoretically using density functional method.
The elastic properties for mono- and poly-crystalline FeSe1-xTex system are
predicted for the first time and the results discussed. Analysis of doping
dependent band characteristics in conjunction with previous studies reveal that
favorable nesting of Fermi surface indicates a possible basis for understanding
why Tc in FeSe1-xTex is maximum for x ~ 0.5.
Keywords: FeSe superconductors, Substitution effect, Elastic properties,
Electronic properties.
PACS: 74.62.Dh, 74.70.Dd, 74.20.Pq, 74.25.LdComment: 11 pages, 5 figure
Superconducting MAX phases Nb2AC (A = S, Sn): An ab-initio study
An ab-initio investigation of structural parameters, elastic, electronic,
thermodynamic and optical properties of MAX phases Nb2AC (A = S, Sn) has been
carried out by the plane wave psedudopotential method based on density
functional theory (DFT). The effect on results of substitution of heavier Sn
atoms for the lighter S atoms in the nanolaminate network has been made. The
analysis of the electronic band structure shows that these compounds are
electrical conductors, with contribution predominantly from the Nb 4d states.
The temperature and pressure dependence of bulk modulus, Debye temperature,
specific heats, thermal expansion coefficient of the nanolaminates are
calculated for the first time using the quasi-harmonic Debye model with
phononic effects. The estimated values of electron-phonon coupling constants
(lambda ~ 0.49, ~0.59) imply that Nb2SC and Nb2SnC are moderately coupled
superconductors. Further first time detailed analysis of all optical functions
reveals that Nb2SC is a better dielectric material, and also both the phases,
having similar reflectivity spectra, show promise as good coating materials in
the energy regions 10-16.5 eV.
Keywords: Nb2SC; Nb2SnC; First-principles; Mechanical properties;
Quasi-harmonic Debye model; Band structure; Thermodynamic properties; Optical
propertiesComment: 12 pages, 7 figures, 2 tables. Modification of text and Fig.
Sulvanite Compounds Cu3TMS4 (TM= V, Nb and Ta): Elastic, Electronic, Optical and Thermal Properties using First-principles Method
We present a systematic first-principles study of the structural, elastic,
electronic, optical and thermodynamics properties of the sulvanite compounds
Cu3TMS4 (TM = V, Nb and Ta). The structural, elastic and electronic properties
are in fact revisited using a different calculation code than that used by
other workers and the results are compared. The band gaps are found to be
1.041, 1.667 and 1.815 eV for Cu3VS4, Cu3NbS4 and Cu3TaS4, respectively which
are comparable to other available calculated results. The optical properties
such as dielectric function, refractive index, photoconductivity, absorption
coefficients, reflectivity and loss function have been calculated for the first
time. The calculated results are compared with the limited measured data on
energy dependent refractive index and reflectivity coefficient available only
for Cu3TaS4. All the materials are dielectric, transparent in the visible
range. The values of plasma frequencies are found to be 15.36, 15.58 and 15.64
eV for Cu3VS4, Cu3NbS4 and Cu3TaS4, respectively. Furthermore, following the
quasi-harmonic Debye model, the temperature effect on the bulk modulus, heat
capacity, and Debye temperature is calculated reflecting the anharmonic phonon
effects and these are compared with both experimental and other theoretical
data where available.Comment: 13 page
Newly synthesized Ti5Al2C3: Electronic and optical properties by first-principles method
A theoretical study of the newly identified Ti5Al2C3 belonging to the MAX
phases has been performed by using the first-principles pseudopotential
plane-wave method within the generalized gradient approximation (GGA). The
energy band structure and optical properties are reported for the first time.
It is seen that Ti 3d electrons mainly contribute to the DOS at the Fermi
level, and should be involved in the conduction properties. The parameters of
optical properties (dielectric function, absorption spectrum, conductivity,
energy-loss spectrum and reflectivity) for Ti5Al2C3 are calculated and
discussed. The material has a large positive static dielectric constant of 130
which indicates it to be a good dielectric material. Further the reflectivity
of Ti5Al2C3 is high in the infrared-visible-UV region up to ~ 9.7 eV showing
promise as a good coating material to avoid solar heating.
Keywords: A: Ti5Al2C3; B: First-principles; C: Electronic structure; C:
Optical propertiesComment: 5 pages, 3 figures, 1 tabl
Phase stability and physical properties of hypothetical V4SiC3
We study the phase stability, mechanical, electronic, optical properties and
Vicker's hardness of the newly predicted layered compound V4SiC3 using the
first-principles method. This hypothetical compound is found to possess higher
bulk modulus as well as higher hardness than those of a similar V4AlC3. The
Mulliken bond population analysis indicates that the substitution of Al atom
with the Si atom increases the Vicker's hardness of this compound. The
electronic band structure shows that the conductivity is metallic and the main
contribution comes from V 3d states. The partial density of states (PDOS) shows
that the hybridization peak of V 3d and C 2s lies lower in energy than that of
V 3d and Si 3p states which suggests that the V 3d - C 2s bond is stronger than
the V 3d - Si 3p bond. The results are consistent with our bond analysis.
Further we have discussed the origin of the features that appear in the optical
properties. V4SiC3 is seen as a promising dielectric material showing a much
better candidate material as a coating to avoid solar heating than those of
V4AlC3, {\alpha}-Nb4SiC3 and Ti4AlN3 compounds.
Keywords: MAX phase V4SiC3; Phase stability; Electronic properties; Optical
properties; Vicker's hardness.
PACS: 61.66.Fn, 62.20.-x, 62.20.Dc, 71.15Mb, 78.20.CiComment: 9 pages, 4 figures, 3 Table, Correction in Fig. 4 (ref 17 changed to
ref 21
Structural, elastic, electronic and optical properties of a newly predicted layered-ternary Ti4SiN3: A First-principles study
We study a newly predicted layered-ternary compound Ti4SiN3 in its {\alpha}-
and {\beta}-phases. We calculate their mechanical, electronic and optical
properties and then compare these with those of other compounds M4AX3 (M = V,
Ti, Ta; A = Si, Al; X = N, C). The results show that the hypothetical Ti4SiN3
shows an improved behavior of the resistance to shape change and uniaxial
tensions and a slight elastic anisotropy. The electronic band structures for
both {\alpha}- and {\beta}-Ti4SiN3 show metallic conductivity in which Ti 3d
states dominate. The hybridization peak of Ti 3d and N 2s lies lower in energy
than that of Ti 3d and Si 3p states which suggests that the Ti 3d - N 2s bond
is stronger than the Ti 3d - Si 3p bond. Using band structure we discuss the
origin of different features of optical properties. The {\alpha}-phase of
predicted compound has improved behavior in reflectivity compared to those of
similar types of compounds.
Keywords: Ternary nitride; First-principles; Mechanical properties;
Electronic band structure; Optical propertiesComment: 9 pages, 6 figures, 2 table
Synthesized inverse-perovskites Sc3InX (X = B, C, N): A theoretical investigation
We present first-principles density functional theory (DFT) investigations of
mechanical, thermodynamic and optical properties of synthesized
inverse-perovskites Sc3InX (X = B, C, N). The elastic constants at zero
pressure and temperature are calculated and the anisotropic behavior of the
compounds is illustrated. All the three materials are shown to be brittle in
nature. The computed Peierls stress, approximately 3 to 5 times larger than of
a selection of MAX phases, show that dislocation movement may follow but with
much reduced occurrences compared to these MAX phases. The Mulliken bonding
population and charge density maps show stronger covalency between Sc and X
atoms compared with Sc-Sc bond. The Vickers hardness values of Sc3InX are
predicted to be between 3.03 and 3.88 GPa. The Fermi surfaces of Sc3InX contain
both hole- and electron-like topology which changes as one replaces B with C or
N. The bulk modulus, specific heats, thermal expansion coefficient, and Debye
temperature are calculated as a function both temperature and pressure using
the quasi-harmonic Debye model with phononic effects. The results so obtained
are analysed in comparison to the characteristics of other related compounds.
Moreover optical functions are calculated and discussed for the first time. The
reflectivity is found to be high in the IR-UV regions up to ~ 10.7 eV (Sc3InB,
Sc3InC) and 12.3 eV (Sc3InN), thus showing promise as good coating materials.
Keywords: Sc3InX, Mechanical properties; Fermi surface; Quasi-harmonic Debye
model; Thermodynamic properties; Optical propertiesComment: 14 pages, 8 figures, 2 tables, some text modifications. arXiv admin
note: substantial text overlap with arXiv:1208.556
Structural, elastic, thermal and lattice dynamic properties of new 321 MAX phases
A new series of MAX family designated as 321 phases are recently reported
with Nb3As2C, V3As2C, Nb3P2C and Ta3P2C. Most of the physical properties of
these new MAX phase compounds are unexplored and the present study aims to
investigate their structural, elastic, thermal, and lattice dynamical
properties. Their mechanical and dynamical stabilities are examined. All the
phases are elastically anisotropic and brittle in nature. The Debye
temperatures and lattice thermal conductivities have been calculated. Lattice
dynamical features are investigated in detail and infrared and Raman modes are
identified. High melting temperature of these compounds are favorable for their
applications at elevated temperatures
Investigating usability of mobile health applications in Bangladesh
Background: Lack of usability can be a major barrier for the rapid adoption
of mobile services. Therefore, the purpose of this paper is to investigate the
usability of Mobile Health applications in Bangladesh.
Method: We followed a 3-stage approach in our research. First, we conducted a
keyword-based application search in the popular app stores. We followed the
affinity diagram approach and clustered the found applications into nine
groups. Second, we randomly selected four apps from each group (36 apps in
total) and conducted a heuristic evaluation. Finally, we selected the highest
downloaded app from each group and conducted user studies with 30 participants.
Results: We found 61% usability problems are catastrophe or major in nature
from heuristic inspection. The most (21%) violated heuristic is aesthetic and
minimalist design. The user studies revealed low System Usability Scale (SUS)
scores for those apps that had a high number of usability problems based on the
heuristic evaluation. Thus, the results of heuristic evaluation and user
studies complement each other.
Conclusion: Overall, the findings suggest that the usability of the mobile
health apps in Bangladesh is not satisfactory in general and could be a
potential barrier for wider adoption of mobile health services.Comment: 13 pages, 4 figure
New MAX Phase Compound Mo2TiAlC2: First-principles Study
A theoretical study of Mo2TiAlC2 compound belonging to the MAX phases has
been performed by using the firstprinciples pseudopotential plane-wave method
within the generalized gradient approximation. We have calculated the
structural, elastic, electronic and optical properties of Mo2TiAlC2. To confirm
mechanical stability, the elastic constants Cij are calculated. Other elastic
parameters such as bulk modulus, shear modulus, compressibility, Young modulus,
anisotropic factor, Pugh ratio, Poisson ratio are also calculated. The energy
band structure and density of states are calculated and analyzed. The results
show that the electrical conductivity is metallic with a high density of states
at the Fermi level in which Mo 4d states dominate. Furthermore, the optical
properties such as dielectric function, refractive index, photoconductivity,
absorption coefficients, loss function and reflectivity are also calculated.
Its reflectance spectrum shows that it has the potential to be used as a
promising shielding material to avoid solar heating.Comment: 9 page
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