Search results for "chemical physics"
showing 10 items of 2553 documents
Ternary transition metals sulfides in hydrotreating catalysis.
2007
International audience; Pure microcrystalline barium molybdate BaMoO4 and barium tungstate BaWO4 materials were prepared by molten flux reaction using alkali metal nitrates as reaction media. The obtained crystals have rhombic shape and expose mostly (111) crystallographic planes. Their mean size depends on the flux temperature and the nature of the alkali metal cation. Monomeric molybdate and tungstate used as precursors yield target products already at 673 K whereas if polymerized ammonium oxosalts were used, then higher temperatures were necessary to obtain barium salts. The optimal temperature for the preparation of pure crystals with well defined shape was found to be near 773 K. UV–vi…
High pressure crystal structures of orthovanadates and their properties
2020
Pressure-induced phase transitions in orthovanadates have led to interesting physical phenomena. The observed transitions usually involve large volume collapses and drastic changes in the electronic and vibrational properties of the materials. In some cases, the phase transitions implicate coordination changes in vanadium, which has important consequences in the physical properties of vanadates. In this Perspective, we explore the current knowledge of the behavior of MVO4 vanadates under compression. In particular, we summarize studies of the structural, vibrational, and electronic properties and a few illustrative examples of high-pressure research in the compounds of interest are discusse…
Insights into Intrinsic Defects and the Incorporation of Na and K in the Cu2ZnSnSe4 Thin-Film Solar Cell Material from Hybrid-Functional Calculations
2016
We have performed density functional theory calculations using the HSE06 hybrid functional to investigate the energetics, atomic, and electronic structure of intrinsic defects as well as Na and K impurities in the kesterite structure of the Cu2ZnSnSe4 (CZTSe) solar cell material. We found that both Na and K atoms prefer to be incorporated into this material as substitutional defects in the Cu sublattice. At this site highly stable (Na–Na), (K–K), and (Na–K) dumbbells can form. While Na interstitial defects are stable in CZTSe, the formation of K interstitial defects is unlikely. In general, the calculated formation energies for Na-related defects are always lower compared to their K-related…
Field effect in the viscosity of magnetic colloids studied by multi-particle collision dynamics
2019
Abstract Colloidal solutions of magnetic nanoparticles are usually employed when the fluidity and magnetic properties are required at the same time, either in technical or biomedical applications. However, when the magnetic size of the nanoparticles is large enough (>12–15 nm) the colloid may form an equilibrium structure with or without the external magnetic field, which can significantly influence its rheology. Using multi-particle collision dynamics we study the internal structure and viscosity of the magnetic colloids at varying magnitudes of the externally applied field. We show a generalized structural behavior across all studied regimes and an appreciable increase of flow resistance …
First experiments on applying the gasdynamic ECR ion source for negative hydrogen ion production
2017
This article has no abstract. peerReviewed
Topological insulator nanoribbon Josephson junctions: Evidence for size effects in transport properties
2020
We have used Bi$_2$Se$_3$ nanoribbons, grown by catalyst-free Physical Vapor Deposition to fabricate high quality Josephson junctions with Al superconducting electrodes. In our devices we observe a pronounced reduction of the Josephson critical current density $J_c$ by reducing the width of the junction, which in our case corresponds to the width of the nanoribbon. Because the topological surface states extend over the entire circumference of the nanoribbon, the superconducting transport associated to them is carried by modes on both the top and bottom surfaces of the nanoribbon. We show that the $J_c$ reduction as a function of the nanoribbons width can be accounted for by assuming that on…
Exploring the transport properties of equatorially low coordinated erbium single ion magnets
2019
Single-molecule spin transport represents the lower limit of miniaturization of spintronic devices. These experiments, although extremely challenging, are key to understand the magneto-electronic properties of a molecule in a junction. In this context, theoretical screening of new magnetic molecules provides invaluable knowledge before carrying out sophisticated experiments. Herein, we investigate the transport properties of three equatorially low-coordinated erbium single ion magnets with C3v symmetry: Er[N(SiMe3)2]3 (1), Er(btmsm)3 (2) and Er(dbpc)3 (3), where btmsm=bis(trimethylsilyl)methyl and dbpc=2,6-di-tert-butyl-p-cresolate. Our ligand field analysis, based on previous spectros…
Ab initio calculations of CaZrO3, BaZrO3, PbTiO3 and SrTiO3 (001), (011) and (111) surfaces as well as their (001) interfaces
2019
We carried out ab initio calculations for technologically important ABO3 perovskites, like, CaZrO3, BaZrO3, PbTiO3 and SrTiO3, their (001), (011) and (111) surfaces as well as (001) interfaces. For...
Explosive crystallization in amorphous CuTi thin films: a molecular dynamics study
2019
Abstract Molecular dynamic simulation was used to study mechanism of self-propagating waves of explosive crystallization (devitrification) in the CuTi metallic glass. Processes in thin rectangular samples composed of one to two million atoms were simulated and compared with experimental data. It was shown that the nucleation of primary crystalline clusters occurs homogeneously due to spontaneous fluctuations of atomic structure; the clusters not
The challenge in realizing an exchange coupled BiFeO3-double perovskite bilayer
2020
Abstract In this work we propose a device design for efficient voltage control of magnetism. The magnetization of a ferrimagnetic double perovskite may be manipulated by an exchange coupled layer of multiferroic BiFeO3. Bilayers of Barium doped BiFeO3 and ferrimagnetic double perovskite Sr2FeMoO6 have been prepared by pulsed laser deposition motivated by the possibility of strong interlayer exchange coupling. While single layers of each material show high quality we observe that in both stacking orders the first layer decomposes during the deposition of the second layer. The reason for the decomposition are strongly differing growth conditions for BiFeO3 and Sr2FeMoO6. This means that the g…