Is RuAs a candidate for high temperature thermoelectric applications?

The mineral inspired material RuAs2 shows promise as a thermoelectric material with its high stability and attractive band structure. In order to validate these expectations phase-pure polycrystalline ruthenium arsenide was synthesized and densified using Spark Plasma Sintering. RuAs2 is an n-type semiconductor with an indirect band gap 0.

generation of stoichiometric HCN and its application in the Pd-catalysed cyanation of aryl bromides: evidence for a transmetallation step between two oxidative addition Pd-complexes.

A protocol for the Pd-catalysed cyanation of aryl bromides using near stoichiometric and gaseous hydrogen cyanide is reported for the first time. A two-chamber reactor was adopted for the safe liberation of generated HCN in a closed environment, which proved highly efficient in the Ni-catalysed hydrocyanation as the test reaction. Subsequently, this setup was exploited for converting a range of aryl and heteroaryl bromides (28 examples) directly into the corresponding benzonitriles in high yields, without the need for cyanide salts.

Exploring the Binding of Barbital to a Synthetic Macrocyclic Receptor. A Charge Density Study.

Experimental charge density distribution studies, complemented by quantum mechanical theoretical calculations, of a host-guest system composed of a macrocycle (1) and barbital (2) in a 1:1 ratio (3) have been carried out via high-resolution single-crystal X-ray diffraction. The data were modeled using the conventional multipole model of electron density according to the Hansen-Coppens formalism. The asymmetric unit of macrocycle 1 contained an intraannular ethanol molecule and an extraannular acetonitrile molecule, and the asymmetric unit of 3 also contained an intraannular ethanol molecule.

X-ray electron density investigation of chemical bonding in van der Waals materials.

Van der Waals (vdW) solids have attracted great attention ever since the discovery of graphene, with the essential feature being the weak chemical bonding across the vdW gap. The nature of these weak interactions is decisive for many extraordinary properties, but it is a strong challenge for current theory to accurately model long-range electron correlations. Here we use synchrotron X-ray diffraction data to precisely determine the electron density in the archetypal vdW solid, TiS, and compare the results with density functional theory calculations.

Structure and Hydrogenation Properties of a HfNbTiVZr High-Entropy Alloy.

A high-entropy alloy (HEA) of HfNbTiVZr was synthesized using an arc furnace followed by ball milling. The hydrogen absorption mechanism was studied by in situ X-ray diffraction at different temperatures and by in situ and ex situ neutron diffraction experiments. The body centered cubic (BCC) metal phase undergoes a phase transformation to a body centered tetragonal (BCT) hydride phase with hydrogen occupying both tetrahedral and octahedral interstitial sites in the structure.

Probing the accuracy and precision of Hirshfeld atom refinement with interfaced with .

Hirshfeld atom refinement (HAR) is a novel X-ray structure refinement technique that employs aspherical atomic scattering factors obtained from stockholder partitioning of a theoretically determined tailor-made static electron density. HAR overcomes many of the known limitations of independent atom modelling (IAM), such as too short element-hydrogen distances, (-H), or too large atomic displacement parameters (ADPs). This study probes the accuracy and precision of anisotropic hydrogen and non-hydrogen ADPs and of (-H) values obtained from HAR.

Structural evolution and stability of Sc(WO) after discharge in a sodium-based electrochemical cell.

Sc(WO), prepared by solid state synthesis and constructed as an electrode, is discharged to different states in half-cell batteries, versus a Na negative electrode. The structural evolution of the Na-containing electrodes is studied with synchrotron powder X-ray diffraction (PXRD) revealing an increase in microstrain and a gradual amorphization taking place with increasing Na content in the electrode. This indicates that a conversion reaction takes place in the electrochemical cell.

Fluoride substitution in LiBH; destabilization and decomposition.

Fluoride substitution in LiBH is studied by investigation of LiBH-LiBF mixtures (9 : 1 and 3 : 1). Decomposition was followed by in situ synchrotron radiation X-ray diffraction (in situ SR-PXD), thermogravimetric analysis and differential scanning calorimetry with gas analysis (TGA/DSC-MS) and in situ infrared spectroscopy (in situ FTIR). Upon heating, fluoride substituted LiBH forms (LiBHF) and decomposition occurs, releasing diborane and solid decomposition products.

Efficient Water Reduction with sp -sp Diboron(4) Compounds: Application to Hydrogenations, H-D Exchange Reactions, and Carbonyl Reductions.

A series of crystalline sp -sp diboron(4) compounds were synthesized and shown to promote the facile reduction of water with dihydrogen formation. The application of these diborons as simple and effective dihydrogen and dideuterium sources was demonstrated by conducting a series of selective reductions of alkynes and alkenes, and hydrogen-deuterium exchange reactions using two-chamber reactors. Finally, as the water reduction reaction generates an intermediate borohydride species, a range of aldehydes and ketones were reduced by using water as the hydride source.

Atomistic Explanation for Interlayer Charge Transfer in Metal-Semiconductor Nanocomposites: The Case of Silver and Anatase.

A concerted theoretical and experimental investigation of the silver/anatase hybrid nanocomposite, a very promising material for advanced sensing applications, is presented. We measure its exceptional electrochemical virtues in terms of current densities and reproducibility, providing their explanation at the atomic-scale level and demonstrating how and why silver acts as a positive electrode. Using periodic plane-wave DFT calculations, we estimate the overall amount of electron transfer toward the semiconductor side of the interface at equilibrium.

The structure-directing amine changes everything: structures and optical properties of two-dimensional thiostannates.

Two different two-dimensional thiostannates (SnS) were synthesized using tris(2-aminoethyl)amine (tren) or 1-(2-aminoethyl)piperidine (1AEP) as structure-directing agents. Both structures consist of negatively charged thiostannate layers with charge stabilizing cations sandwiched in-between. The fundamental building units are SnS broken-cube clusters connected by double sulfur bridges to form polymeric (SnS) honeycomb hexagonal layers.

Synthesis, stability and Li-ion mobility of nanoconfined LiBH.

This communication presents the first synthesis of nanoconfined Lithium closo-borate, LiBH, using nanoporous SiO as scaffold. The yield of LiBH is up to 94 mol%. The as-synthesized nanoconfined LiBH exhibits a structural transition around 380 °C and conversion to H-deficiency LiBH at 580 °C.

Crystal structure across the β to α phase transition in thermoelectric Cu Se.

The crystal structure uniquely imparts the specific properties of a material, and thus provides the starting point for any quantitative understanding of thermoelectric properties. Cu Se is an intensely studied high performing, non-toxic and cheap thermoelectric material, and here for the first time, the average structure of β-Cu Se is reported based on analysis of multi-temperature single-crystal X-ray diffraction data. It consists of Se-Cu layers with additional copper between every alternate layer.

Accurate charge densities from powder X-ray diffraction - a new version of the Aarhus vacuum imaging-plate diffractometer.

In recent years powder X-ray diffraction has proven to be a valuable alternative to single-crystal X-ray diffraction for determining electron-density distributions in high-symmetry inorganic materials, including subtle deformation in the core electron density. This was made possible by performing diffraction measurements in vacuum using high-energy X-rays at a synchrotron-radiation facility. Here we present a new version of our custom-built in-vacuum powder diffractometer with the sample-to-detector distance increased by a factor of four.

Redox-Driven Migration of Copper Ions in the Cu-CHA Zeolite as Shown by the In Situ PXRD/XANES Technique.

Using quasi-simultaneous in situ PXRD and XANES, the direct correlation between the oxidation state of Cu ions in the commercially relevant deNO NH -SCR zeolite catalyst Cu-CHA and the Cu ion migration in the zeolitic pores was revealed during catalytic activation experiments. A comparison with recent reports further reveals the high sensitivity of the redox-active centers concerning heating rates, temperature, and gas environment during catalytic activation. Previously, Cu was confirmed present only in the 6R.

Revealing the slow decomposition kinetics of type-I clathrate BaGaGe.

Inconsistencies in high temperature thermoelectric property measurements of BaGaGe have prompted our study on the thermal stability of this heavily studied inorganic clathrate. Using X-ray diffraction, thermal analysis, and imaging techniques on both powder and spark plasma sintered pelletized samples, we probe the structure and decomposition characteristics of this important high temperature thermoelectric material. We demonstrate that the decomposition of BaGaGe is extremely dependent on the heating conditions employed and, as a result of the slow decomposition kinetics of the clathrate, reveal that the true stability of this system has been overlooked in the extensive literature available.

Synthesis, structures and thermal decomposition of ammine MBH complexes (M = Li, Na, Ca).

A series of ammine metal-dodecahydro-closo-dodecaboranes, MBH·nNH (M = Li, Na, Ca) were synthesized and their structural and thermal properties studied with in situ time-resolved synchrotron radiation powder X-ray diffraction, thermal analysis, Fourier transformed infrared spectroscopy, and temperature-programmed photographic analysis. The synthesized compounds, LiBH·7NH, NaBH·4NH and CaBH·6NH, contain high amounts of NH, 43.3, 26.

Carrier concentration dependence of structural disorder in thermoelectric Sn Te.

SnTe is a promising thermoelectric and topological insulator material. Here, the presumably simple rock salt crystal structure of SnTe is studied comprehensively by means of high-resolution synchrotron single-crystal and powder X-ray diffraction from 20 to 800 K. Two samples with different carrier concentrations (sample = high, sample = low) have remarkably different atomic displacement parameters, especially at low temperatures.

The chemistry of ZnWO nanoparticle formation.

The need for a change away from classical nucleation and growth models for the description of nanoparticle formation is highlighted. By the use of total X-ray scattering experiments the transformation of an aqueous polyoxometalate precursor mixture to crystalline ZnWO nanoparticles under hydrothermal conditions was followed. The precursor solution is shown to consist of specific Tourné-type sandwich complexes.

High-Temperature Crystal Structure and Chemical Bonding in Thermoelectric Germanium Selenide (GeSe).

The discovery of the ultra-high thermoelectric figure of merit of 2.6 in SnSe has drawn attention to other lead-free IV-VI orthorhombic semiconductors. GeSe has been predicted to possess thermoelectric performances comparable to SnSe.

Variable-temperature structural studies on valence tautomerism in cobalt bis(dioxolene) molecular complexes.

A variable-temperature single-crystal structural study of five valence tautomeric cobalt molecular complexes, Co(3,5-DBSQ)(DBPy) (1), Co(3,5-DBSQ)(DBPy)·1.33CH (1S), Co(3,5-DBSQ)(DCPy)·CH (2S), Co(3,5-DBSQ)(TBPy) (3) and Co(3,5-DBSQ)(TCPy) (4) (S = toluene, 3,5-DBSQ = 3,5-di-tert-butylsemiquinonate, DBPy = 3,5-dibromopyridine, DCPy = 3,5-dichloropyridine, TBPy = 3,4,5-tribromopyridine and TCPy = 3,4,5-trichloropyridine) is reported. The re-crystallization of (1S) in toluene at 277 K resulted in a concomitant formation of a solvent-free polymorph, Co(3,5-DBSQ)(DBPy) (1).

Metal borohydrides and derivatives - synthesis, structure and properties.

A wide variety of metal borohydrides, MBH, have been discovered and characterized during the past decade, revealing an extremely rich chemistry including fascinating structural flexibility and a wide range of compositions and physical properties. Metal borohydrides receive increasing interest within the energy storage field due to their extremely high hydrogen density and possible uses in batteries as solid state ion conductors. Recently, new types of physical properties have been explored in lanthanide-bearing borohydrides related to solid state phosphors and magnetic refrigeration.

Low-Temperature Anharmonicity in Cesium Chloride (CsCl).

Anharmonic lattice vibrations govern heat transfer in materials, and anharmonicity is commonly assumed to be dominant at high temperature. The textbook cubic ionic defect-free crystal CsCl is shown to have an unexplained low thermal conductivity at room temperature (ca. 1 W/(m K)), which increases to around 13  W/(m K) at 25 K.

A Close Look at the Structure of the TiO-APTES Interface in Hybrid Nanomaterials and Its Degradation Pathway: An Experimental and Theoretical Study.

The surface functionalization of TiO-based materials with alkylsilanes is attractive in several cutting-edge applications, such as photovoltaics, sensors, and nanocarriers for the controlled release of bioactive molecules. (3-Aminopropyl)triethoxysilane (APTES) is able to self-assemble to form monolayers on TiO surfaces, but its adsorption geometry and solar-induced photodegradation pathways are not well understood. We here employ advanced experimental (XPS, NEXAFS, AFM, HR-TEM, and FT-IR) and theoretical (plane-wave DFT) tools to investigate the preferential interaction mode of APTES on anatase TiO.