254 research outputs found
Elastic properties of superconducting MAX phases from first principles calculations
Using first-principles density functional calculations, a systematic study on
the elastic properties for all known superconducting MAX phases (Nb2SC, Nb2SnC,
Nb2AsC, Nb2InC, Mo2GaC and Ti2InC) was performed. As a result, the optimized
lattice parameters, independent elastic constants, indicators of elastic
anisotropy and brittle/ductile behavior as well as the so-called machinability
indexis were calculated. We derived also bulk and shear moduli, Young's moduli,
and Poisson's ratio for ideal polycrystalline MAX aggregates. The results
obtained were discussed in comparison with available theoretical and
experimental data and elastic parameters for other layered superconductors.Comment: 7 page
Sn1-xBixO2 and Sn1-xTaxO2 (0 \leq x \leq 0.75): A first-principles study
The structural, elastic, electronic and optical (x = 0) properties of doped
Sn1-xBixO2 and Sn1-xTaxO2 (0 \leq x \leq 0.75) are studied by using the
first-principles pseudopotential plane-wave method within the local density
approximation. The independent elastic constants Cij and other elastic
parameters of these compounds have been calculated for the first time. The
mechanical stability of the compounds with different doping concentrations has
also been studied. The electronic band structure and density of states are
calculated and the effect of doping on these properties is also analyzed. It is
seen that the band gap of the undoped compound narrowed with dopant
concentration which disappeared for x = 0.26 for Bi doping and 0.36 for Ta
doping. The materials thus become conductive oxides through the change in the
electronic properties of the compound for x \leq 0.75 which may be useful for
potential application. The calculated optical properties, e.g. dielectric
function, refractive index, absorption spectrum, loss-function, reflectivity
and conductivity of the undoped SnO2 in two polarization directions are
compared with both previous calculations and measurements.
Keywords: Doped SnO2; First-principles; Mechanical properties; Electronic
band structure; Optical properties.Comment: 10 pages, 5 figures, added 10 more references, comparison with
mearements mad
Structural, Elastic, Electronic and Optical Properties of a New Layered-Ternary Ta4SiC3 Compound
We propose a new layered-ternary Ta4SiC3 with two different stacking
sequences ({\alpha}- and {\beta}-phases) of the metal atoms along c axis and
study their structural stability. The mechanical, electronic and optical
properties are then calculated and compared with those of other compounds M4AX3
(M = V, Nb, Ta; A = Al, Si and X = C). The predicted compound in the
{\alpha}-phase is found to possess higher hardness than any of these compounds.
The independent elastic constants of the two phases are also evaluated and the
results discussed. The electronic band structures for {\alpha}- and
{\beta}-Ta4SiC3 show metallic conductivity. Ta 5d electrons are mainly
contributing to the total density of states (DOS). We see that the
hybridization peak of Ta 5d and C 2p lies lower in energy and the Ta 5d-C 2p
bond is stronger than Ta 5d-Si 3p bond. Further an analysis of the different
optical properties shows the compound to possess improved behavior compared to
similar types of compounds.Comment: 9 pages, 5 figures; PACS: 60.20.Dc; 62.20.-x; 71.15.Mb; 78.20.Ci;
Keywords: Ta4SiC3, First-principles; Elastic properties; Electronic
properties; Optical propertie
Synthesis and DFT investigation of new bismuth-containing MAX phases
The M(n + 1)AX(n) phases (M = early transition metal; A = group A element and X = C and N) are materials exhibiting many important metallic and ceramic properties. In the present study powder processing experiments and density functional theory calculations are employed in parallel to examine formation of Zr(2)(Al(1−x)Bi(x))C (0 ≤ x ≤ 1). Here we show that Zr(2)(Al(1−x)Bi(x))C, and particularly with x ≈ 0.58, can be formed from powders even though the end members Zr(2)BiC and Zr(2)AlC seemingly cannot. This represents a significant extension of the MAX phase family, as this is the first report of a bismuth-based MAX phase
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