M. M. Hossain

Phase stability, elastic, electronic, thermal and optical properties of Ti3Al1−xSixC2 (0≤x≤1): First principle study

The structural parameters with stability upon Si incorporation and elastic, electronic, thermodynamic and optical properties of Ti3Al1� xSixC2 (0rxr 1) are investigated systematically by the plane wave pseudopotential method based on the density functional theory (DFT). The increase of some elastic parameters with increasing Si-content renders the alloys to possess higher compressive and tensile strength. The Vickers hardness value obtained with the help of Mulliken population analysis increases as x is increased from 0 to 1. The solid solutions considered are all metallic with valence and conduction bands, which have a mainly Ti 3d character, crossing the Fermi level. The temperature and pressure dependences of bulk modulus, normalized volume, specific heats, thermal expansion coefficient, and Debye temperature are all obtained through the quasi-harmonic Debye model with phononic effects for T¼ 0 � 1000 K and P¼ 0 � 50 GPa. The obtained results are compared with other results available. Further an analysis of optical functions for two polarization vectors reveals that the reflectivity is high in the visible–ultraviolet region up to � 10.5 eV region showing promise as a good coating material. & 2012 Elsevier B.V. All rights reserved.

Newly synthesized Zr2AlC, Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX phases: A DFT based first-principles study

The structural, elastic, and electronic properties of newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX nanolaminates have been studied using first-principles density functional theory (DFT) calculations for the first time. Theoretical Vickers hardness has also been estimated for these compounds. All the calculated results are compared with experimental data and also with that of recently discovered Zr2AlC phase, where available. Zr2(Al0.58Bi0.42)C and Zr2(Al0.2Sn0.8)C are the two first Bi and Sn containing MAX compounds. The calculated structural parameters are found to be in good agreement with the experimental data. The single crystal elastic constants Cij and other polycrystalline elastic coefficients have been calculated and the mechanical stabilities of these compounds have been theoretically confirmed. The bulk modulus increases and the shear modulus decreases due to partial Bi/Sn/Sb substitution for Al in Zr2AlC. The calculated elastic moduli show that these Bi/Sn/Sb containing MAX phases are more anisotropic than Zr2AlC, and have a tendency towards ductility. The Vickers hardness decreases in the Bi/Sn/Sb containing compounds. Further, the electronic band structures and electronic density of states (EDOS) are calculated and the effects of different elemental substitution on these properties are investigated. The electronic band structures show metallic characteristics with contribution predominantly coming from the Zr 4d orbitals. Partial presence of Bi/Sn/Sb atoms increases the EDOS at the Fermi level to some extent. Possible implications of the theoretical results for these recently discovered MAX nanolaminates have been discussed in detail in this paper.

Newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX phases: A first-principles study

The structural, elastic, and electronic properties of newly synthesized Zr2(Al0.58Bi0.42)C, Zr2(Al0.2Sn0.8)C, and Zr2(Al0.3Sb0.7)C MAX nanolaminates have been studied using first-principles density functional theory (DFT) calculations for the first time. Theoretical Vickers hardness has also been estimated for these compounds. All the calculated results are compared with experimental data and also with that of recently discovered Zr2AlC phase, where available. Zr2(Al0.58Bi0.42)C and Zr2(Al0.2Sn0.8)C are the two first Bi and Sn containing MAX compounds. The calculated structural parameters are found to be in good agreement with the experimental data. The single crystal elastic constants Cij and other polycrystalline elastic coefficients have been calculated and the mechanical stabilities of these compounds have been theoretically confirmed. The bulk modulus increases and the shear modulus decreases due to partial Bi/Sn/Sb substitution for Al in Zr2AlC. The calculated elastic moduli show that these Bi/Sn/Sb containing MAX phases are more anisotropic than Zr2AlC, and have a tendency towards ductility. The Vickers hardness decreases in the Bi/Sn/Sb containing compounds. Further, the electronic band structures and electronic density of states (EDOS) are calculated and the effects of different elemental substitution on these properties are investigated. The electronic band structures show metallic characteristics with contribution predominantly coming from the Zr 4d orbitals. Partial presence of Bi/Sn/Sb atoms increases the EDOS at the Fermi level to some extent. Possible implications of the theoretical results for these recently discovered MAX nanolaminates have been discussed in detail in this paper.

Effects of lamp power and mirror position on the interface shape of the silicon molten zone during infrared convergent heating

The effects of lamp power and mirror position on the feed–melt and crystal–melt interfaces during the growth of a silicon crystal were examined using the mirror-shifting-type infrared convergent-heating floating-zone (IR-FZ) method. The lamp power used to form the molten zone was carefully changed. The positions of the mirrors along a horizontal plane were also systematically shifted from positions close to the molten zone to more distant positions as compared with the conventional mirror position. The solid–liquid (S–L) interfaces at both the feed–melt and the crystal–melt sides were examined carefully at the different mirror positions under the different lamp powers using a feed rod 15 mm in diameter, and it was found that the convexities (h/r) of the S–L interface shapes at both sides decreased with increasing lamp power. It was also found that the interface shapes were independent of the mirror position. A lower lamp power was enough to maintain the stable molten zone during the crystal growth at the closer mirror position. Therefore, effective heating was realized at the closer mirror position.

Comparative study of Mo2Ga2C with superconducting MAX phase Mo2GaC: First-principles calculations

The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states (DOS) is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters (e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function) are calculated for the first time. The study of dielectric constant (ɛ 1) indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of T c expression using available parameter values (DOS, Debye temperature, atomic mass, etc.) suggests that the compound is less likely to be superconductor.

First‐Principles Study of Superconducting ScRhP and ScIrP Pnictides

For the first time, we have reported in this study an ab initio investigation on elastic properties, Debye temperature, Mulliken population, Vickers hardness, and charge density of the two recently synthesized superconducting ScRhP and ScIrP pnictides. The optimized cell parameters show fair agreement with the experimental results. The mechanical stability of both ternary phosphides is confirmed via the calculated elastic constants. Both compounds are ductile in nature and damage tolerant. ScIrP is expected to be elastically more anisotropic than ScRhP. The estimated value of Debye temperature predicts that ScRhP is thermally more conductive than ScIrP and the phonon frequency in ScRhP is higher than that in ScIrP. Both pnictides are soft and easily machinable due to their low Vickers hardness. Moreover, the hardness of ScRhP is lower due to the presence of antibonding Rh-Rh in ScRhP. The metallic conductivity of ScRhP reduces significantly when Rh is replaced with Ir. The main contribution to the total density of states (TDOS) at Fermi-level (EF) comes from d-electrons of Sc and Rh/Ir in both pnictides. These two ternary compounds are characterized mainly by metallic and covalent bonding with little ionic contribution. The calculated superconducting transition temperatures fairly coincide with the reported measured values.

Predicted MAX Phase Sc 2 InC: Dynamical Stability, Vibrational and Optical Properties

The calculations of phonon dispersion, thermodynamic and optical properties including charge density, Fermi surface, Mulliken population analysis, theoretical Vickers hardness of predicted Sc 2 InC have been performed for the first time. The Sc 2 InC is mechanically as well as dynamically stable. It is promising for optoelectronic devices in the visible and ultraviolet energy regions and as a coating material to avoid solar heating.

Axis symmetry of silicon molten zone interface shape under a mirror-shifting-type infrared convergent-heating floating-zone method

The shape of the silicon crystal, whether spiral or cylindrical, was grown using the infrared convergent-heating floating-zone method, and the stability of the molten zone depended on the position of the mirror-lamp (M-L) system with respect to the grown crystal and molten zone. Through experiment, we studied the changes in the molten zone shape: the melt/feed, melt/gas, and melt/crystal interface shapes of the silicon molten zone under different positions of the M-L system. Although conventional parameters such as convexities (h/r) of the interface toward the melt were found to be independent of the position of the M-L system, the asymmetry of the zone length, L, was found to be inversely proportional to the distance of the M-L system from the center of the molten zone. A spiral crystal would be grown in this case. We introduce some parameters such as growth interface angle (δ), triple point angle (TPA), meniscus angle (MA), and altitude of the interface curvature (aC) to characterize the axis symmetry of the melt/gas and melt/crystal interfaces. The variations in TPA, MA, and aC were significantly reduced when the M-L system was shifted to a distant position from the center of the molten zone. On the other hand, the variations in δ were independent of the position of the M-L system. Thus, a symmetric molten zone was observed when the M-L system was at a distant rather than a close position. These behaviors were validated through observations of the molten zone stability and the crystal shape.

Crystal structure of S-octyl (E)-3-(4-meth­oxy­benzyl­idene)di­thio­carbazate

As already observed in similar molecules, the dithiocarbazate group in the title compound, C17H26N2OS2, adopts an EE configuration with respect to the C=N bond of the benzylidene moiety. In the crystal, molecules are connected into inversion dimers by pairs of N—H⋯S hydrogen bonds. The dimers are linked by weak π–π interactions, with centroid-to-centroid distances of 3.723 (11) Å, forming chains parallel to [110].

Crystal structure of bis-{S-hexyl 3-[4-(di-methyl-amino)-benzyl-idene]di-thio-carbazato-κ(2) N (3),S}copper(II).

In the title complex, the CuII atom exhibits a square-planar coordination geometry and is located on a crystallographic inversion centre, leading to a trans configuration of the N,S-chelating ligands.