Actinide metals and intermetallic compounds: Electronic structure and magnetic properties

Cohesive properties are calculated for the AnIr₂ and AnRh₃ series of intermetallic systems. The positive and negative deviations from Vegard's law found in both series are emphasized. The development of magnetism and 5f localization as a function of increasing actinide atomic number is studied in detail for the two classes of compounds. A relativistic formulation of the Stoner criterion for ferromagnetism is presented and applied to a number of actinide systems. Finally the ferromagnetism of UFe₂, NpFe₂ and PuFe₂ is treated theoretically. For these intermetallic compounds it is found necessary to implement all three Hund's rules into the calculations, before agreement with experiment is obtained.     

Thermodynamic and crystallographic properties of REPd intermetallic compounds

REPd phases have been extensively studied both by thermal, crystallographic, thermodynamic and micrographic methods. As a result of this investigation a possible sequence of structures is proposed which is correlated with the thermal and thermodynamic data.Europium is a divalent rare earth in EuPd while ytterbium in YbPd seems to be present with certain, fixed percentage of atoms in the trivalent state.     

Synthesis and catalytic properties of nanoparticulate intermetallic Ga-Pd compounds

A two-step synthesis for the preparation of single-phase and nanoparticulate GaPd and GaPd(2) by coreduction of ionic metal-precursors with LiHBEt(3) in THF without additional stabilizers is described. The coreduction leads initially to the formation of Pd nanoparticles followed by a Pd-mediated reduction of Ga(3+) on their surfaces, requiring an additional annealing step. The majority of the intermetallic particles have diameters of 3 and 7 nm for GaPd and GaPd(2), respectively, and unexpected narrow size distributions as determined by disk centrifuge measurements. The nanoparticles have been characterized by XRD, TEM, and chemical analysis to ensure the formation of the intermetallic compounds. Unsupported nanoparticles possess high catalytic activity while maintaining the excellent selectivity of the ground bulk materials in the semihydrogenation of acetylene. The activity could be further increased by depositing the particles on α-Al(2)O(3).     

Hydrogen absorption properties of selected uranium intermetallic compounds

Some results of an investigation of hydrogen absorption by selected intermetallic compounds of uranium and thorium with nickel, cobalt, manganese and palladium are reported. Of the compounds under consideration, ThNiAl and UNiAl revealed the greatest capability for hydrogen absorption. The basic thermodynamic functions were calculated for hydrides of both these compounds and the lattice constants were determined by an X-ray method.     

Magnetic properties of Ln3In intermetallic compounds

Results of magnetic studies of Ln₃In phases (Ln = Pr, Nd, Gd, Dy and Er) are presented. All materials exhibited Curie-Weiss behavior in the paramagnetic regions with effective moments approximating $\text{g[J(J + 1)]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for the tripositive ion. Positive Weiss constants were observed indicating predominance of ferromagnetic exchange. Pr₃In and Nd₃In order ferromagnetically at 62 and 114 K, respectively. However, the ordered moment is less than 10% of gJ. Dy₃In and Er₃In also seem to order ferromagnetically, but with low moments compared to gJ. Gd₃In exhibits metamagnetic behavior with a critical field of about 5 kOe. Neutron diffraction measurements on Nd₃In indicate that it is ferromagnetic and confirm the low Nd³⁺ moment.     

Synthesis,structure, and properties of the new intermetallic compounds SrPdTl2 and SrPtTl2

The title compounds have been synthesized and characterized structurally and through property measurements and electronic structure calculations. Single-crystal X-ray diffraction analyses reveal that the two compounds crystallize in an orthorhombic system, MgCuAl(2) type (Cmcm, Z = 4, a = 4.486(2), 4.491(3) A, b = 10.991(5), 10.990(6) A, c = 8.154(1), 8.140(4) A for SrPdTl(2), and SrPtTl(2), respectively). The structure can be directly derived from that of hexagonal SrTl(2) (CaIn(2) type) in which four-bonded thallium atoms in shared puckered hexagons generate tunnels. The Pd or Pt is encapsulated (with symmetry reduction) on the side of each tunnel within a distorted trigonal prism. Band structure calculations (EHTB) on both SrTl(2) and SrPdTl(2) demonstrate the effects of the conversion, with strong Pd-Tl bonding and appreciable electron transfer from Tl to Pd. Property measurements show that SrPdTl(2) is metallic, as expected.     

Synthesis,characterization, and thermal properties of new flavor compounds

Synthesis, characterization, and thermal properties of new, flavor, long chain esters were presented. The new compounds were obtained in the catalytic esterification process of a stoichiometric ratio of trans-3,7-dimethyl-2,6-octadien-1-ol, succinic anhydride, and aliphatic chain diol. As diols ethylene glycol, 1,4-buthylene glycol, 1,5-pentylene glycol, and 1,6-hexylene glycol were applied. The spectroscopic analyses completely confirmed that the applied synthesis conditions allowed obtaining the new compounds with high yield and purity. Their thermal properties were studied in inert and oxidative atmospheres. The esters were less thermally stable in inert (IDT 186–195 °C) than in oxidative (IDT 210–228 °C) atmosphere. Two, non-completely divided decomposition steps were visible during their pyrolysis. In contrast, the new, long chain compounds decompose in three major steps in air. The analyses of the volatile products emitted during their pyrolysis indicated on the asymmetrical disrupt of their bonds. The formation of acyclic and alicyclic monoterpene hydrocarbons, succinic anhydride, diols, alcohols, alkenes, and water was observed. It indicated mainly on the β-elimination reactions during their pyrolysis. Also, β-elimination reactions of esters are mainly expected in air. Initially, it resulted in the formation of acyclic and alicyclic monoterpene hydrocarbons, hydroxyl compounds (diols, alcohols), and its β-elimination products: aldehydes, alkenes, and water. However, the presence of oxygen in the medium causes the partial decarboxylation and oxygenation of aldehydes and thus the formation of alkenes and carbon dioxide. In addition, the beginning of evaporation of succinic anhydride was detected at T _max1. At T _max2 the evaporation of succinic anhydride, their partial decarboxylation to CO₂, the small amounts of diols, alcohols, and aldehyde fragments were indicated. Finally, succinic anhydride, water, and carbon dioxide were only observed during decomposition of studied esters in air.     

Structural,elastic, electronic and thermal properties of the cubic perovskite-type BaSnO3

First-principles calculations are performed to investigate the structural, elastic, electronic and thermal properties of the cubic perovskite-type BaSnO₃. The ground-state properties are in agreement with experimental data. The independent elastic constants, C₁₁, C₁₂ and C₄₄, are calculated from direct computation of stresses generated by small strains. A linear pressure dependence of the elastic stiffnesses is found. From the theoretical elastic constants, we have computed the elastic wave velocities along [100], [110] and [111] directions. The shear modulus, Young's modulus, Poisson's ratio, Lamé’s coefficients, average sound velocity and Debye temperature are estimated in the framework of the Voigt-Reuss-Hill approximation for ideal polycrystalline BaSnO₃ aggregate. Using the sX-LDA for the exchange-correlation potential, the calculated indirect fundamental band gap value is in very good agreement with the measured one. The analysis of the site-projected l-decomposed density of states, charge transfer and charge density shows that the bonding is of ionic nature. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the temperature effect on the lattice constant, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature is calculated.     

Structural and thermal properties of Co-Cu-Fe hydrotalcite-like compounds

The structural properties and thermal decomposition processes of Co-Cu-Fe ternary hydrotalcites (HT) have been studied through X-ray diffraction, thermogravimetric measurements, Fourier-transform infrared and Mössbauer spectroscopies. Due to the strong Jahn-Teller effect, the Cu-Fe layered system is stabilized only in the presence of Co²⁺. At low Co²⁺ contents, additional phases are segregated in the solids. X-ray patterns show the presence of Cu(OH)₂ and CuO. The decomposition process was investigated by in situ X-ray, in situ Mössbauer and FTIR experiments. By increasing the temperature from 25 °C up to 180 °C we observed that the structural disorder increases. This effect has been likely attributed to the Co²⁺→Co³⁺ oxidation since thermal decomposition was carried out under static air atmosphere. Part of the Co³⁺ cations could migrate to the interlayer region, thus forming a metastable compound that still has a layered structure. Collapse of the layered structure was observed at about 200 °C. By further increasing the temperature the system becomes more crystalline and the formation of Co₃O₄ is observed in the X-ray patterns. In Cu-rich HT, some of the carbonate anions are released at temperatures higher than 550 °C and this phenomenon is attributed to the formation of a carbonate-rich phase. The specific surface area data present its highest values in the temperature range where the collapse of the layered structure takes place.     

Synthesis and thermal properties of spiro phosphorus compounds

Intumescent materials, 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro-[5,5]-undecane-3,9-dioxide and 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro-[5,5]-undecane having the capacity to produce dehydrating agent, blowing agent, and undergo carbonization during burning have been synthesized. The thermal behavior of the synthesized materials was investigated using differential thermal analysis, thermal volatilization analysis, programmed vacuum pyrolysis–mass spectrometry, flash pyrolysis–mass spectrometry and off-line pyrolysis–gas chromatography–mass spectrometry. The materials show exothermic degradation after 250 °C. Monitoring the release of hydrogen chloride and water, the blowing agents for the production of carbon foam, clearly indicated the superior performance of the pentavalent phosphorus compound over the trivalent phosphorus compound. The major gaseous degradation products released during pyrolysis showed the presence of sufficient quantities of several alkyl-substituted benzenes and fused aromatics. Suitable degradation mechanism has been proposed and discussed to explain the formation of various organics during thermal degradation.     

Uranyl compounds and complexes: Electronic structure,chemical bonding and spectral properties

The electronic structure of solid compounds -UO₃, Cs₂UO₂CL₄, UO₂F₄ and complexes UO ₂ ²⁺ and UO₂(NO₃)₂ · 2H₂O has been studied by the cluster discrete variational DV X method in Dirac-Slater and Hartree-Fock-Slater approximation. The analysis of relativistic effects in the electronic structure of uranyl compounds was based on the comparison of non-relativistic and relativistic DV results. The interpretation of X-ray photoelectron spectra of -UO₃ and Cs₂UO₂Cl₄ basing on the MO model is given. The various electronic states contributions to the chemical bonding in uranyl compounds are investigated.     

The electrochromic properties of lutetium and other phthalocyanines

The electrochemical properties of thin films of metal phthalocyanines on conducting substrates are investigated. The electrochromism of lutetium diphthalocyanine is discussed and a film electrode model is proposed based on an irreversible charge transfer step. This model accounts for the main concentration and voltammetric sweep-rate dependencies. The lifetime of lutetium diphthalocyanine films under continuous redox reactions in aqueous solution is restricted due to chemical attack by hydroxide ions. The electrochromic effect is displayed by other phthalocyanines; in monophthalocyamines it is associated with oxidation and reduction of the metal atom. Tin diphthalocyanine behaves similarly to lutetium diphthalcyanine, the redox reaction occurring at the phthalocyanine rings.     

Electronic spectra, solvatochromic behavior and acid-base properties of some azo cinnoline compounds

The electronic spectra of three azo cinnoline derivatives have been studied in pure and mixed organic solvents of different characteristics as well as the effect of concentration of the compounds in the different solvents. The different bands observed have been assigned to the proper electronic transition. The longer wavelength band displayed by the para nitro cinnoline derivative in dimethylformamide (DMF) solution is assigned to an intermolecular CT transition. The solvated H-bonding complexes formed between DMF and the para nitro derivative were investigated. DeltaG and K(f) values of these complexes have been determined. The acidity constants of the para nitro compound were determined from the spectra in aquous-methanolic solution of varying pH values. The effect of temperature on the longer wavelength visible band of p-NO(2) has been investigated.     

Electronic properties of spiro compounds for organic electronics

The electronic properties of p-type, n-type, and ambipolar spiro materials have been investigated using a combination of photoemission spectroscopy, electron energy-loss spectroscopy, and density functional based calculations. Our results provide insight into the occupied density of states as well as the electronic excitation spectra. Comparison of experimental and theoretical data allows the identification of the orbitals responsible for charge transport and optical properties.     

Thorium compounds with non-metals: Electronic structure, chemical bond, and physicochemical properties

The current state of research on the nature of the chemical bond and the physicochemical properties of binary Th-X (X = H, B, C, N, O, P, S, As, Se, Sb) and ternary (carbonitrides, thorates, and silicates) thorium compounds by modern ab initio methods of the band structure theory is reviewed. The possibilities of the ab initio band structure methods in describing the structural states, phase stability, elasticity characteristics, X-ray emission, absorption, and photoelectron spectra of thorium-containing systems are discussed.     

First-principles studies of Al-Ni intermetallic compounds

The structural properties, heats of formation, elastic properties, and electronic structures of Al-Ni intermetallic compounds are analyzed here in detail by using density functional theory. Higher calculated absolute values of heats of formation indicate a very strong chemical interaction between Al and Ni for all Al-Ni intermetallic compounds. According to the computational single crystal elastic constants, all the Al-Ni intermetallic compounds considered here are mechanically stable. The polycrystalline elastic modulus and Poisson's ratio have been deduced by using Voigt, Reuss, and Hill (VRH) approximations, and the calculated ratio of shear modulus to bulk modulus indicated that AlNi, Al₃Ni, AlNi₃ and Al₃Ni₅ compounds are ductile materials, but Al₄Ni₃ and Al₃Ni₂ are brittle materials. With increasing Ni concentration, the bulk modulus of Al-Ni intermetallic compounds increases in a linear manner. The electronic energy band structures confirm that all Al-Ni intermetallic compounds are conductors.