Adlane Sayede

Density functional calculations of the structural, electronic, and ferroelectric properties of high-k titanate Re2Ti2O7 (Re= La and Nd)

We have studied the structural, electronic, and ferroelectric properties of La2Ti2O7 (LTO) and Nd2Ti2O7 (NTO) by first-principles density functional theory calculations. The computed structural parameters are found to be in good agreement with experimental findings. In particular, the P21 phase is confirmed to be energetically preferred over the other configurations for both titanates. The calculations revealed the possible existence of an unidentified phase, namely, the P21/m paraelectric structure. From the modern theory of polarization the spontaneous polarization of LTO and NTO was calculated to be 7.72 μC/cm2 and 7.42 μC/cm2, respectively, in accordance with experimental findings. Its origin is ascribed to the displacement of the rare earth (Re) cations in the [100] cleavage plane and parallel to the b axis. Electronic charge density distributions and Bader’s topological analysis indicates that the bonding interactions between Re and O as well as Ti and O are not purely ionic, a noticeable covalent b...

Alkaline-earth metal hydrides as novel host lattices for Eu(II) luminescence.

Luminescence of divalent europium has been investigated for the first time in metal hydrides. A complete solid-solution series was found for the pseudobinary system Eu(x)Sr(1-x)H(2) [a = 637.6(1) pm -12.1(3)x pm, b = 387.0(1)-6.5(2)x pm, c = 732.2(2)-10.1(4)x pm]. Europium-doped alkaline-earth hydrides Eu(x)M(1-x)H(2) (M = Ca, Sr, Ba) with a small europium concentration (x = 0.005) exhibit luminescence with maximum emission wavelengths of 764 nm (M = Ca), 728 nm (M = Sr), and 750 nm (M = Ba); i.e., the emission energy of divalent europium shows an extremely large red shift compared to the emission energies of fluorides or oxides. Theoretical calculations (LDA+U) confirm decreasing band gaps with increasing europium content of the solid solutions.

A Property-Matched Water-Soluble Analogue of the Benchmark Ligand PPh3

A series of sulfonated biphenylphosphanes were readily prepared from commercially available, inexpensive, and air-stable organic compounds. Of these, the trisulfonated trisbiphenylphosphane can be considered as a true water-soluble analogue of PPh(3) as the cone angle and basicity of both phosphanes are very close and result in a similar coordination mode on palladium and rhodium complexes. The catalytic performance of the trisulfonated trisbiphenylphosphane was evaluated in the aqueous hydroformylation of 1-decene and the Tsuji-Trost reaction.

A novel theoretical design of electronic structure and half-metallic ferromagnetism in the 3d (V)-doped rock-salts SrS, SrSe, and SrTe for spintronics

The exploration of new dilute magnetic semiconductors (DMSs) designed for the development of practical semiconductor spintronics devices has attracted increasing interest in recent years. In the present study, we have investigated the structural, electronic and magnetic properties of strontium chalcogenide semiconductors (SrS, SrSe and SrTe) doped with the transition metal vanadium (V) in the rock-salt structure as Sr1−xVxZ (Z = S, Se and Te) ternary DMSs at a concentration x = 0.125, using first-principles calculations of density functional theory with the generalized gradient approximation functional of Wu and Cohen (GGA-WC). The electronic structure of each compound revealed half-metallic (HM) ferromagnetic behavior with a HM gap and 100% spin polarization. The HM gap is an important parameter in determining the importance of DMSs in spintronics; it is 0.937, 0.585 and 0.245 eV for Sr0.875V0.125S, Sr0.875V0.125Se and Sr0.875V0.125Te, respectively. Therefore, the Sr0.875V0.125Z (Z = S, Se and Te) seems to be a new potential candidate for future spintronics applications.

Relaxed energetic maps of κ‐carrabiose: A DFT study

The B3LYP density function was used with the 6‐31G(d) basis set to perform relaxed energetic contour maps of the charged form of κ‐carrabiose in the gas phase and for the neutral form first in the gas phase and then by simulating the presence of water as solvent using the Onsager model. Only one starting conformation has been considered to perform all the calculations. Rigid energetic maps have been then constructed either by addition of diffuse or polarization functions to the basis set obtaining in that way 6‐31+G(d)//6‐31G(d), 6‐31+G(d,p)//6‐31G(d), and 6‐311++G(d,p)//6‐31G(d) energetic maps that have been carefully examined. The obtained structures corresponding to the lower energy conformers have been then fully optimized using different basis sets with the B3LYP method, a reversion in term of energy has been observed for the two first minima in the case of the charged disaccharide in the gas phase, this was attributed to the large grid of 30° that could lead to the exclusion of an intermediate value corresponding to the real minimum of energy. We thus suggest that after establishing potential energy maps it is essential to proceed to full optimizations of the lower energy conformers. Calculations using the more accurate correlated method MP2 with the 6‐31G(d) basis set have also been performed for conformers of the two disaccharides in the gas phase.

Electronic and optical properties of layered RE2Ti2O7 (RE = Ce and Pr) from first principles

We have studied the structural and electronic properties of Ce2Ti2O7 (CeTO) and Pr2Ti2O7 (PrTO) by first-principles density functional theory calculations. The computed structural parameters are in fairly good agreement with the available experimental findings. Band structure calculations using the GGA+U approach predict an insulating ground state for the herein studied compounds. The insulating band gaps of 2.00 eV and 2.83 eV are found for CeTO and PrTO, respectively. The analysis of the density of states reveals that the strongly localized RE 4f levels act as charge-trapping sites, predicting a lower photocatalytic activity for CeTO. We have also calculated the optical properties for both CeTO and PrTO. Based on these properties, it is predicted that these titanates are insensitive to ultra-violet radiation, while they are more sensitive to frequencies of the radiation in visible and early UV regions.

New supramolecular amphiphiles based on renewable resources

The complexation between esters derived from sorbitol and β-cyclodextrin was studied. Isosorbide dioleate and sorbitan trioleate formed well-defined inclusion complexes with β-cyclodextrin and these inclusion complexes exhibited surfactant behaviour.

Density functional conformational study of 2-O-sulfated 3,6 anhydro-α-D-galactose and of neo-κ- and ι-carrabiose molecules in gas phase and water

We examined the conformational preferences of the 2-O-sulfated-3,6-α-D-anhydrogalactose (compound I) and two 1,3 linked disaccharides constituting-κ or ι-carrageenans using density functional and ab initio methods in gas phase and aqueous solution. Systematic modifications of two torsion angles leading to 324 and 144 starting geometries for the compound I and each disaccharide were used to generate adiabatic maps using B3LYP/6-31G(d). The lower energy conformers were then fully optimized using B3LYP, B3PW91 and MP2 with several basis sets. Overall, we discuss the impact of full relaxation on the energy and structure of the dominant conformations, present the performance comparison with previous molecular mechanics calculations if available, and determine whether our results are impacted, when polarization and diffuse functions are added to the 6-31G(d) basis set, or when the MP2 level of theory is used.

A self-emulsifying catalytic system for the aqueous biphasic hydroformylation of triglycerides

The Rh-catalyzed hydroformylation of the CC double bonds of triglycerides (T) was performed in aqueous medium through the formation of supramolecular complexes resulting from the inclusion of the alkenyl chains of T into the cavity of modified cyclodextrins (CDs). Mixing T and the aqueous catalytic phase in the presence of CDs led to emulsions that were characterized by phase diagrams and nephelometric measurements. Variations of the nature of the CDs, the reaction temperature, the CO/H2 pressure and the nature of the catalyst allowed for the optimization of the catalytic conditions. The concept was efficiently applied to commercial oils. Molecular dynamics simulations corroborated the experimental data.

Microstructure and oxidation resistance of relaxed epitaxial nickel thin films grown on (100)- and (110)-SrTiO3 substrates by pulsed laser deposition

The relaxed epitaxial growth of Ni thin films has been successfully performed on both (100)- and (110)-oriented SrTiO3 substrates by pulsed laser deposition, as revealed by pole figures realized by X-ray micro-diffraction and rocking curve measurements. In the case of Ni films deposited on the (110)-SrTiO3 substrate, the advanced microstructural X-ray diffraction study (ω-scans vs. φ and reciprocal space maps) evidences the existence of two domains disoriented with respect to the substrate crystallographic axes (both in-plane with +5° and −5° tilts (±1°) and out-of-plane with +3.7° and −3.7° tilts (±0.1°), respectively). Besides the lattice misfit constraints, the layer orientation can also be controlled by strain/surface energy balance. The surface energy modeling of nickel makes it possible to explain the observed growth by low surface energy anisotropy. Furthermore, the high temperature oxidation resistance of the films under air has been studied by in situ high-temperature X-ray diffraction. While the results show the formation of a NiO oxide layer which retains the initial orientation of the Ni film, the Ni corrosion temperature is found to be 500 °C and 375 °C when grown on (100)- and (110)-SrTiO3 substrates, respectively. Such a high corrosion temperature for Ni films grown on the (100)-SrTiO3 substrate is linked to their high density, as observed by atomic force microscopy.