Computational study of mechanical stability and phonon properties of MXenes Mo2ScC2T2(T = O and F): 2D materials

The structural, electronic, elastic, and phonon properties of pristine Mo2ScC2 and surface terminated Mo2ScC2T2 (T = O and F) were investigated by employing density functional theory calculations. Generalized gradient approximation was used to model exchange-correlation effects. The electronic band structure was calculated using both Perdew-Burke-Ernzerhof and Heyd-Scuseria-Ernzerhof functional and found that all considered materials are metallic. Elastic constants, Young's moduli, shear moduli, in-plane stiffnesses, and Poisson's ratios were tabulated and showed that pristine Mo2ScC2 and surface terminated Mo2ScC2T2 satisfy the mechanical stability criteria. Furthermore, Mo2ScC2O2 has been found to be a significant candidate for ultrasensitive sensors due to its ultrahigh Young's modulus. The absence of the imaginary line in phonon band structures confirms the dynamic stability of Mo2ScC2, Mo2ScC2O2, and Mo2ScC2F2. Furthermore, Debye temperatures, phonon group velocities, thermodynamic properties, and Grüneisen parameters were calculated for Mo2ScC2 and Mo2ScC2O2. Finally, it is understood that Mo2ScC2 and Mo2ScC2O2 are suitable candidates for applications that require low thermal conductivity

Comparative studies on the solvent extraction of transition metal cations by calixarene, phenol and ester derivatives.

The ionophore solvent extraction of various alkali metal and transition metal cations from the aqueous phase to the organic phase was carried out by using diazo-coupling calix[n]arenes [p-(4-phenylazophenylazo)calix[4]arene (L1) and p-phenylazocalix[6]arene (L2)], phenol derivatives [2,6-dimethyl-3-phenylazophenol (L3), 2-(5-bromo-2-pyridylazo)-5-diethylamino phenol (L4), 2-chloro-4-nitro(phenylazo)-5-sec-butyl-2-phenol (L5) and 2-chloro-4-nitro(phenylazo)-5-tert-butyl-2-phenol (L6)], and ester derivatives [quinoline-8-benzoate (L7), phenyl-1,4-dibenzoate (L8), p-tolyltiobenzoate (L9)]. It was found that, all the compounds (L1-L9) examined showed selectivity for transition metal cations such as Ag+, Hg+ Hg2+, and poor efficiency for alkali metal cations (Na+ and K+). The best extraction efficiency was obtained with L1 and L4

The elastic, electronic, and optical properties of PtSi and PtGe compounds

The structural, mechanical, electronic and optical properties of orthorhombic PtSi and PtGe were investigated using norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters and bulk modulus for PtSi and PtGe have been compared with the experimental and theoretical values. The second-order elastic constants were calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities and Debye temperature have also been estimated. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valance electrons and the effective optical dielectric constant were calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. © 2011 Taylor & Francis

Origin of low thermal conductivity in monolayer PbI2

The mechanical, dynamical, and thermodynamic properties of monolayer PbI2 were investigated comprehensively via first-principles calculations. The generalized gradient approximation was chosen for exchange-correlation effects. Thermodynamical properties, Debye temperature, sound velocity, charge density, Grüneisen parameter, and thermal conductivity were examined in detail. The present elastic constants and phonon spectra have shown that PbI2 is stable both mechanically and dynamically. It was revealed that the relationship among atomic mass, interatomic bonds, phonon scattering, specific heat, sound velocities, Grüneisen parameter, and Debye temperature cause low thermal conductivity. These results are matching with is predictions of Slack's theory

A first-principle study of the structural and lattice dynamical properties of CaX (X=S, Se, and Te)

WOS: 000266245900002We have studied structural, elastic, thermodynamic (Debye temperature and melting temperature), and lattice dynamical (phonon dispersion curves, heat capacity, and entropy) properties of CaX via ab initio calculations within the local density approximations. The results are compared with the available experimental and other theoretical data, and the agreement is, generally, quite good. We also predict the temperature and/or pressure-dependent behaviors of some mechanical, lattice dynamical, and thermodynamic properties for the same compounds.Gazi University [05/2008-16]This work was supported by the Gazi University Research Project Unit under Project No: 05/2008-16

A first-principles study on the structural, elastic, vibrational, and thermodynamical properties of BaX (X = S, Se, and Te)

WOS: 000263940300022Ab-initio calculations based on norm-conserving pseudopotentials and density functional theory (DFT) have been performed to investigate the structural, elastic, thermodynamic, and lattice dynamical (phonon dispersion curves) properties of BaX in rock-salt (B1) and CsCl (132) structures. The results support the experimental and theoretical data in the existing literature. Findings are also presented for the temperature-dependent behaviors of some thermodynamic properties such as entropy, heat capacity, internal energy, and free energy for the same compounds in the B1 phase. (C) 2008 Elsevier Ltd. All rights reserved.Gazi University [05/2008-16]This work is supported by the Gazi University Research-Project Unit under Project no. 05/2008-16

Seasonal and needle age-related variationsin the biochemical characteristics of Pinus nigrasubsp. Pallasiana (Lamb.) Holmboe

Variations in the photosynthetic pigments and total carbohydrate contents of needles of different age classes (current-year, 1-year-old, 2-year-old and 3-year-old) of Pinus nigra subsp. pallasiana (Lambert) Holmboe trees in a young natural stand were investigated during the growing season. In current-year needles, total carbohydrate content was lower during June and July when the needle growth continued than in older age classes, but it was similar to other age classes in the months of August to October. Seasonal patterns of variations in total carbohydrate content were almost similar in 1-, 2-, and 3-year-old needles. Chlorophyll and carotenoid contents increased from May to June, remained relatively constant or declined slightly during summer and autumn in 1-, 2-, and 3-year-old needles. In October, the pigment content was highest in 1-year-old needles, and lowest in 3-year-old needles. Our study indicated that total carbohydrate and pigment contents were affected by needle age classes and seasons. © 2018 Czech Academy of Agricultural Sciences. All rights reserved

Transformation of bonds and redistribution of partial states of valence electrons at α(С23)-WGe 2 →β(С11b )-WGe 2 high-pressure polymorphic transformation

The electronic properties and phase transition of β(C11b)-WGe2 and α(C23)-WGe2 phases were investigated via x-ray emission spectroscopy method and first-principles calculations. The analysis of the comparison of the partial energy distributions of the valence electrons of the β(C11b)-WGe2 and α(C23)-WGe2 phases was also studied. The transformation of interatomic bonds during the polymorphic transition α(C23)-WGe2→β(C11b)-WGe2 under comprehensive compression was proposed. The first-principles calculations showed that the phase transition from the α(C23)-WGe2 phase to the β(C11b)-WGe2 phase occurs under high pressure. Furthermore, the electronic structure calculations indicate that the considered phases are metallic in nature. The results have revealed that the fine-structure peculiarities of the WLβ 5- and GeKβ 2-emission bands match well with the main peaks of the partial densities of the W d- and Ge p- electronic states for the both phases