Influence of uniaxial tensile stress on the mechanical and piezoelectric properties of short-period ferroelectric superlattice

Tetragonal ferroelectric/ferroelectric BaTiO3/PbTiO3 superlattice under uniaxial tensile stress along the c axis is investigated from first principles. We show that the calculated ideal tensile strength is 6.85 GPa and that the superlattice under the loading of uniaxial tensile stress becomes soft along the nonpolar axes. We also find that the appropriately applied uniaxial tensile stress can significantly enhance the piezoelectricity for the superlattice, with piezoelectric coefficient d33 increasing from the ground state value by a factor of about 8, reaching 678.42 pC/N. The underlying mechanism for the enhancement of piezoelectricity is discussed

Subfemtosecond steering of hydrocarbon deprotonation through superposition of vibrational modes

Subfemtosecond control of the breaking and making of chemical bonds in polyatomic molecules is poised to open new pathways for the laser-driven synthesis of chemical products. The break-up of the C-H bond in hydrocarbons is an ubiquitous process during laser-induced dissociation. While the yield of the deprotonation of hydrocarbons has been successfully manipulated in recent studies, full control of the reaction would also require a directional control (that is, which C-H bond is broken). Here, we demonstrate steering of deprotonation from symmetric acetylene molecules on subfemtosecond timescales before the break-up of the molecular dication. On the basis of quantum mechanical calculations, the experimental results are interpreted in terms of a novel subfemtosecond control mechanism involving non-resonant excitation and superposition of vibrational degrees of freedom. This mechanism permits control over the directionality of chemical reactions via vibrational excitation on timescales defined by the subcycle evolution of the laser waveform

Effects of La Dopant on Nanocluster Size and Optical Band Gap of CdO Films Prepared by Sol-Gel Method

The undoped and lanthanum doped cadmium oxide thin films were prepared by sol-gel method. The CdO films were doped with various percentages of La, 0.1, 0.5, 1, and 2 at.%. We have investigated the structural properties of the CdO films by atomic force microscopy. The obtained results show that both the grain size and the surface roughness of CdO films reduce with increase of La doping content. Additionally, the result shows a significant decrease of the transmittance in the range of 300 to 500 nm with increase of La doping level. The optical band gap of CdO films increases with La doped CdO films. It was found that the band gaps to be 2.25, 2.36, 2.4, 2.28, and 2.31 eV for La contents with 0.1, 0.5, 1, and 2 at.% doped CdO, respectively

density functional study of the electronic properties of bismuth subcarbonate Bi2O2CO3

Starting from the X-ray diffraction data of Huang et al. we have optimized the atomic positions by minimization of the forces (1 mRy/au) using Perdew-Burke-Ernzerhof generalized gradient approximation (GGA). From the relaxed geometry the electronic structure and the chemical bonding are determined. We have employed the full potential linear augmented plane wave (FPLAPW) method as embodied in the WIEN2k code. In order to get a better estimate of the energy gap we have used the modified Becke-Johnson potential (mBJ) exchange-correlation potential. Our calculations show that the conduction band minimum (CBM) is situated at the centre of the Brillouin zone (BZ) and the valence band maximum (VBM) is located between W and T symmetry points of the BZ, indicating that bismuth subcarbonate is a semiconductor with an indirect band gap of about 0.8 eV. The electrons effective mass ratio (m(e)(*)/me) around G point are calculated. The partial density of states and the electronic charge density distribution shows that there exists a strong covalent bond between C and O atoms. Our calculated bond lengths and angles show very good agreement with the experimental data. (C) 2014 Elsevier Masson SAS. All rights reserve

Density functional study of electronic, charge density, and chemical bonding properties of 9-methyl-3-Thiophen-2-YI-Thieno [3,2-e] [1,2,4] Thriazolo [4,3-c] pyrimidine-8-Carboxylic acid ethyl ester crystals

A comprehensive theoretical density functional investigation of the electronic crystal structure, chemical bonding, and the electron charge densities of 9-Methyl-3-Thiophen-2-YI-Thieno [3, 2-e] [1, 2, 4] Thriazolo [4,3-c] Pyrimidine-8-Carboxylic Acid Ethyl Ester (C15H12N4O2S2) is performed. The density of states at Fermi level equal to 5.50 (3.45) states/Ry cell, and the calculated bare electronic specific heat coefficient is found to be 0.95 (0.59) mj/mole-K-2 for the local density approximation (Engel-Vosko generalized gradient approximation). The electronic charge density space distribution contours in (1 0 0) and (1 1 0) planes were calculated. We find that there are two independent molecules (A and B) in the asymmetric unit exhibit intramolecular C-H center dot center dot center dot O, C-H center dot center dot center dot N interactions. This intramolecular interaction is different in molecules A and B, where A molecule show C-H center dot center dot center dot O interaction while B molecule exhibit C-H center dot center dot center dot N interaction. We should emphasis that there is pi-pi interaction between the pyrimidine rings of the two neighbors B molecules gives extra strengths and stabilizations to the superamolecular structure. The calculated distance between the two neighbors pyrimidine rings found to be 3.345 angstrom, in good agreement with the measured one (3.424(1) angstrom)

Structural, electronic, optical and thermodynamic properties of cubic REGa3 (RE = Sc or Lu) compounds: ab initio study

Structural, elastic, optoelectronic and thermodynamic properties of REGa3 (RE = Sc and Lu) compounds have been studied self consistently by employing state of the art full potential (FP) linearized (L) approach of augmented plane wave (APW) plus local orbitals method. Calculations were executed at the level of Perdew-Burke and Ernzerhof (PBE) parameterized generalized gradient approximation (GGA) for exchange correlation functional in addition to modified Becke-Johnson (mBJ) potential. Our obtained results of lattice parameters show reasonable agreement to the previously reported experimental and other theoretical studies. Analysis of the calculated band structure of ScGa3 and LuGa3 compounds demonstrates their metallic character. Moreover, a positive value of calculated Cauchy pressure, in addition to reflecting their ductile nature, endorses their metallic character as well. To understand optical behavior calculations related to the important optical parameters; real and imaginary parts of the dielectric function, reflectivity R(ω), refractive index n(ω) and electron energy-loss function L(ω) have also been performed. In the present work, thermodynamically properties are also investigated by employing lattice vibrations integrated in quasi harmonic Debye model. Obtained results of volume, heat capacity and Debye temperature as a function of temperature for both compounds, at different values of pressure, are found to be consistent. The calculated value of melting temperature for both compounds (ScGa3 and LuGa3) is found to be similar to the experimental data with an underestimation of 5%

X-ray photoelectron spectrum, X-ray diffraction data, and electronic structure of chalcogenide quaternary sulfide Ag2In2GeS6: experiment and theory

We report measurements of the X-ray diffraction and X-ray photoelectron spectrum on single crystals of Ag2In2GeS6. We also present first principles calculations of the band structure and density of states using the state-of-the-art full potential augmented plane wave method with different possible approximation for the exchange correlation potential. In this paper, we make a detailed comparison of the density of states deduced from the X-ray photoelectron spectra with our calculations. The theoretical results of the density of states are in reasonable agreement with the X-ray photoelectron spectroscopy (VB-XPS) measurements with respect to peak positions. The calculated density of states shows there is a strong hybridization between the states in the valence and conduction bands states. We have calculated the electron charge density distribution in the (100) and (110) planes. In the plane (100), there exists Ag, In, and S atoms, while the plane (110) Ag, S, and Ge atoms are present. The bonding properties are obtained from the charge density distributions. The calculation show that there is partial ionic and strong covalent bonding between Ag-S, In-S, and Ge-S atoms depending on Pauling electro-negativity difference of S (2.58), Ge (2.01), Ag (1.93), and In (31.78) atoms

Elastıc, electronıc and thermodynamıc propertıes of rh3x ( x = zr, nb and ta) ıntermetallıc compounds

WOS: 000330643000005Structural, electronic, elastic and thermodynamic properties of Rh3X ( X = Zr, Nb, Ta) intermetallic compounds are investigated in the framework of density functional theory (DFT). The exchange-correlation (XC) potential is treated with the generalized gradient approximation (GGA) and local density approximation (LDA). The computed ground state properties agree well with the available theoretical and experimental values. The elastic constants are obtained by calculating the total energy versus volume conserving strains using Mehl model. The electronic and bonding properties are discussed from the calculations of band structures (BSs), densities of states and electron charge densities. The volume and bulk modulus at high pressure and temperature are investigated. Additionally, thermodynamic properties such as the heat capacity, thermal expansion and Debye temperature at high pressures and temperatures are also analyzed.Deanship of Scientific Research at King Saud University [RPG-VPP-088]The authors R. K., A. B., Z. A. A. and S. B. O acknowledge the financial support by the Deanship of Scientific Research at King Saud University for funding the work through the research group project No. RPG-VPP-088. The author A. Sayede thanks the Centre de Ressources Informatiques (CRI) of the University of Lille for providing the computational facilities

Experimental and theoretical investigation of the electronic structure and optical properties of TlHgCl3 single crystal

We have synthesized single crystals of TlHgCl3, which posses an orthorhombic symmetry, space group Pnma, with lattice constants a = 9.1601(4) angstrom, b = 4.3548(2) angstrom and c = 14.0396(5) angstrom. The measurements of the optical absorption of TlHgCl3 are performed on parallel-plate samples with polished optical quality surfaces of d = 0.03 mm. The band gap is estimated to be 2.74 eV from the position of fundamental absorption edge at alpha = 200 cm(-1). We have used our measured crystallographic data of TlHgCl3 as input data for calculating the electronic band structure, density of states, electronic charge density and the optical properties. The all-electron full potential linearized augmented plane wave plus local orbital (FP-L(APW + lo)) method is used. Calculations are performed with three types of exchange correlations; local density approximation (LDA), general gradient approximation (PBE-GGA) and the recently modified Becke-Johnson potential (mBJ). The PBE-GGA is used to optimize the atomic positions by minimization of the forces (1 mRy/au) acting on the atoms. The obtained values of the band gap from various exchange correlations are 2.39 eV (LDA), 2.55 eV (PBE-GGA) and 2.69 eV (mBJ). It is clear that mBJ succeeded by a large amount in bringing the calculated energy gap closer to the experimental one. The calculated electronic band structure exhibits that the conduction band minimum and the valence band maximum are located at Z point of the BZ, resulting in a direct band gap. The calculated density of states provides information about the hybridization between the states and the bonding nature. The electronic charge density show that Hg and Cl atoms form partial ionic/covalent bonding between Cl-Hg-Cl. Furthermore, for a deep insight into the electronic structure we have investigated the optical properties