Properties Of Th Research Articles

High-pressure lattice dynamics and thermodynamic properties of Th: Anab initiostudy of phonon dispersion curves

Phonon dispersion curves and thermodynamics of actinides are hardly accessible for both theory and experiments. In this paper we present an ab initio study of the thermodynamics properties of thorium within the framework of the quasiharmonic approximation and by using density-functional theory and the pseudopotential method. First we compare the phonon spectrum we obtained at zero pressure with inelastic neutron scattering experiments. Thereafter we use the phonon dispersions to obtain the $PVT$ equations of state and derive thermodynamic quantities from the free energy. Then we compare our results for the thermal volume expansion, bulk modulus, heat capacity, or Debye temperature with experimental values when existing. The results show a promising agreement with experiment and propose several predictive behaviors.

Extended networks, porous sheets, and chiral frameworks. Thorium materials containing mixed geometry anions: Structures and properties of Th(SeO 3)(SeO 4), Th(IO 3) 2(SeO 4)(H 2O) 3·H 2O, and Th(CrO 4)(IO 3) 2

Three novel Th(IV) compounds containing heavy oxoanions, Th(SeO 3)(SeO 4) ( 1), Th(IO 3) 2(SeO 4)(H 2O) 3·H 2O ( 2), and Th(CrO 4)(IO 3) 2 ( 3), have been synthesized under mild hydrothermal conditions. Each of these three distinct structures contain trigonal pyramidal and tetrahedral oxoanions. Compound 1 adopts a three-dimensional structure formed from ThO 9 tricapped trigonal prisms, trigonal pyramidal selenite, SeO 3 2–, anions containing Se(IV), and tetrahedral selenate, SeO 4 2–, anions containing Se(VI). The structure of 2 contains two-dimensional porous sheets and occluded water molecules. The Th centers are found as isolated ThO 9 tricapped trigonal prisms and are bound by four trigonal pyramidal iodate anions, two tetrahedral selenate anions, and three coordinating water molecules. In the structure of 3, the Th(IV) cations are found as ThO 9 tricapped trigonal prisms. Each Th center is bound by six IO 3 1– anions and three CrO 4 2– anions forming a chiral three-dimensional structure. Second-harmonic generation of 532 nm light from 1064 nm radiation by a polycrystalline sample of 3 was observed. Crystallographic data (193 K, Mo Kα, λ = 0.7 1 0 7 3 ): 1; monoclinic, P2 1/ c; a = 7.0 3 5 1 ( 5 ) Å , b = 9.5 2 5 9 ( 7 ) Å , c = 9.0 2 6 6 ( 7 ) Å , β = 1 0 3.1 2 8 ( 1 ) , Z = 4 , R ( F ) = 2.4 7 % for 91 parameters with 1462 reflections with I > 2 σ ( I ) ; 2, monoclinic, P2 1/ n, a = 7.4 8 8 9 ( 9 ) Å , b = 8.0 0 2 ( 1 ) Å , c = 2 0.1 6 5 ( 3 ) Å , β = 1 0 0.1 4 2 ( 2 ) , Z = 4 , R ( F ) = 4.7 1 % for 158 parameters with 2934 reflections with I > 2 σ ( I ) ; 3, orthorhombic, P2 12 12 1, a = 7.3 6 7 2 ( 5 ) Å , b = 9.3 6 1 7 ( 6 ) Å , c = 1 1.9 2 0 1 ( 7 ) Å , Z = 4 , R ( F ) = 2.0 4 % for 129 parameters with 2035 reflections with I > 2 σ ( I ) .

Atomistic simulation for the structural properties of Th–T and Th–T–In compounds (T = Fe, Co, Ni, Cu)

A series of lattice inversion pair potentials are used to evaluate the phase stability and corrresponding structures for 32 kinds of thorium intermetallics. In particular, the site preference of In atoms in ThCu 6 compound is studied. The calculated results agree well with experiments; this indicates the effectiveness of these potentials for studying the structural properties of these thorium compounds. In addition, the phase stability of ThT 5, Th 2T 17, Th 3T 29 and ThT 12 (T = Fe, Co, Ni) are evaluated and compared also with the same potentials.

ChemInform Abstract: Synthesis and Electronic Properties of Th—N Films.

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Antioxidant properties of Thonningianin A, isolated from the African medicinal herb, Thonningia sanguinea

The antioxidant properties of Thonningianin A (Th A), an ellagitannin, isolated from the methanolic extract of the African medicinal herb, Thonningia sanguinea were studied using the NADPH and Fe2+/ascorbate-induced lipid peroxidation (LPO), electron spin resonance spectrometer and the deoxyribose assay. Th A at 10μM inhibited both the NADPH and Fe2+/ascorbate-induced LPO in rat liver microsomes by 60% without inhibitory effects on cytochrome P450 activity. Th A was similar to the synthetic antioxidant, tannic acid, as an inhibitor of both the NADPH and Fe2+/ascorbate-induced LPO but potent than gallic acid, vitamin C and vitamin E. While Th A poorly scavenged the hydroxyl radical generated by the Fenton reaction it dose-dependently scavenged 1,1-diphenyl-2-picrylhydrazyl, superoxide anion and peroxyl radicals with ic50 of 7.5, 10 and 30μM, respectively. Furthermore, Th A showed inhibitory effects on the activity of xanthine oxidase with an ic50 of 30μM. In the deoxyribose assay both T. sanguinea and its methanolic component Th A showed only site-specific (Fe3++H2O2) but not non-site-specific (Fe3++EDTA+H2O2) hydroxyl radical scavenging suggesting chelating ability for iron ions. Spectroscopic studies showed that Th A enhanced absorbance in the visible region in the presence of Fe2+ ions. These results indicate that the antioxidant properties of Th A involve radical scavenging, anti-superoxide formation and metal chelation.

Synthesis and electronic properties of Th–N films

Thin layers of Th, ThN, and Th3N4 were synthesized by sputter deposition of Th in an Ar atmosphere with variable nitrogen partial pressure. The phase purity and crystal structure of the nitrides were confirmed by X-ray diffraction. Photoelectron spectroscopy studies demonstrate that ThN is metallic, with a rather high density of 6d states at the Fermi level, while Th3N4 is non-metallic.

Electronic structure, phase stability, and chemical bonding inTh2AlandTh2AlH4

We present the results of theoretical investigation on the electronic structure, bonding nature and ground state properties of Th$_2$Al and Th$_2$AlH$_4$ using generalized-gradient-corrected first-principles full-potential density-functional calculations. Th$_2$AlH$_4$ has been reported to violate the "2 \AA rule" of H-H separation in hydrides. From our total energy as well as force-minimization calculations, we found a shortest H-H separation of 1.95 {\AA} in accordance with recent high resolution powder neutron diffraction experiments. When the Th$_2$Al matrix is hydrogenated, the volume expansion is highly anisotropic, which is quite opposite to other hydrides having the same crystal structure. The bonding nature of these materials are analyzed from the density of states, crystal-orbital Hamiltonian population and valence-charge-density analyses. Our calculation predicts different nature of bonding for the H atoms along $a$ and $c$. The strongest bonding in Th$_2$AlH$_4$ is between Th and H along $c$ which form dumb-bell shaped H-Th-H subunits. Due to this strong covalent interaction there is very small amount of electrons present between H atoms along $c$ which makes repulsive interaction between the H atoms smaller and this is the precise reason why the 2 {\AA} rule is violated. The large difference in the interatomic distances between the interstitial region where one can accommodate H in the $ac$ and $ab$ planes along with the strong covalent interaction between Th and H are the main reasons for highly anisotropic volume expansion on hydrogenation of Th$_2$Al.

Critical evaluation of the thermal properties of Th0 2 and Th 1− yU y0 2 and a survey of the literature data on Th 1− yPu y0 2

The thermal properties of Th0 2 and Th 1− y U y 0 2 are critically assessed. These properties include melting point, heat capacity, enthalpy of formation, oxygen potential, thermal conductivity and linear thermal expansion. The literature survey of the thermal properties of Th 1− y PU y O 2 shows a limited amount of data, as a result a critical evaluation is not possible. In addition, the phase diagrams of the binary systems Th0 2−U0 2 and Th0 2−Pu0 2 are discussed.

Magnetic, Transport and Thermal Properties of Ce2CuxAl17-x

To clarify the heavy fermion properties of Th 2 Zn 17 -type Ce 2 Cu x Al 17- x (6.75 ≤ x ≤8.25), we have systematically measured the electrical resistivity including the magnetoresistance, the magnetic susceptibility and the specific heat. In the electrical resistivity measurement for x =8.0, no magnetic order was clearly observed down to 60 mK and the magnetic contribution to the specific heat, C m / T , reached extremely large values of C m / T =3.0 (at 0.7 K), 2.4 (at 0.8 K) and 1.7 J/K 2 mol-Ce (at 1.4 K) for x =8.0, 7.5 and 7.0, respectively. A T 2 dependence of the electrical resistivity was also observed below 0.4 K for x =8.0 and below 0.6 K for x =7.0 and 7.5, indicating that Ce 2 Cu x Al 17- x is a coherent heavy fermion system. However, the possibility of the coexistence of short-range magnetic order resulting from the random distribution of Cu and Al could not be entirely excluded. We discuss the large C m / T values at temperatures close to 0 K in terms of the x dependence of the Kondo temper...

Tb impurities in Th: A Kondo system with undercompensated magnetic moment?

Dilute TbxTh1−x alloys have been thoroughly studied in the light of a possible valence instability and Kondo effect in Tb3+ and Tb4+ ions. We review the experimental data for the specific heat, magnetic susceptibility, magnetization, magnetoresistivity, and the change of the superconducting properties of Th. In analogy to Tm (Tm2+ and Tm3+) and Pr (Pr3+ and Pr4+) impurities in metals, Tb involves two electronic configurations each with a magnetic Hund’s rule ground multiplet. Two classes of models for valence admixtures of two magnetic configurations have been investigated in the past. Depending on the form of the hybridization and the jj coupling within the 4f shell, the models either have a singlet or a magnetic ground state. As for Tm impurities the latter class of models, related to the undercompensated Kondo effect, appears to describe the system TbTh more appropriately. A qualitative explanation of the data is attempted within a scheme that combines Kondo screening with crystalline field splitting.

A Mössbauer effect study of the microscopic magnetic properties of Th2Fe17 and its nitride, Th2Fe17N2.6

The Mössbauer spectra of Th2Fe17 and Th2Fe17N2.6 have been measured at various temperatures between 85 and 295 K and analyzed with a model that is based on the Wigner–Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron-diffraction measurements or band-structure calculations. Upon nitrogenation of Th2Fe17, the 85 K weighted average isomer shift increases from 0.037 to 0.156 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed in their Wigner–Seitz cell volumes and the presence of a nitrogen near neighbor for two of the sites. The nonmagnetic thorium in Th2Fe17N2.6 yields an easy axis of magnetization which, in contrast to magnetic rare earths in R2Fe17 and R2Fe17Nx, is in a general basal direction and not oriented along one of the basal axes. The isomer shift and its temperature dependence for both Th2Fe17 and its nitride are very similar to those observed in related rare-earth R2Fe17 compounds and their nitrides. Upon nitrogenation of Th2Fe17, the 85 K weighted average hyperfine field increases from 256.3 to 336.5 kOe. However, the increases on the 6c and 18f sites are smaller than those observed on the 9d and 18h sites; changes which are in agreement with changes in the magnetic moments observed by neutron diffraction and calculated for the nitrogenation of Nd2Fe17, Gd2Fe17, and Y2Fe17.

Change of magnetic properties of Th2Fe17 due to interstitial solution of C and N

The changes in magnetic and crystallographic properties in the series Th2Fe17Cx and Th2Fe17Nx have been studied. The changes in the latter series were also studied by 57Fe Mössbauer spectroscopy. The ultimate enhancements of the saturation moments in these series are 13% and 24%, respectively. This is much larger than observed previously in the corresponding rare-earth compounds, although the Curie temperature enhancements are of comparable magnitude. In the Th–Fe–C system a novel compound of the BaCd11 type was found, having a Curie temperature around 370 K.

The Effect of Sm, Eu and Yb on the Thermoelectric Properties of Th3P4,-Type Lanthanum Sulfide

ABSTRACTThe Th3P4-type lanthanum sulfides are n-type semiconductors and a continuous series of solid solutions is found between the compositions of La3S4 and La2S3. These materials are attractive for use in high temperature thermoelectric applications because of their high melting points, low thermal conductivities and their inherent ability to vary the electron concentration from a maximum of 6.02 × 1021 cm−3 for La3S4 to zero for La2S3 (i.e., self-doping). In this study, La3S4 compounds in which trivalent La has been partially substituted by divalent Sm, Eu or Yb (La3−xMxS4 , x = 0.1 to 0.9) have been prepared by the pressure assisted reaction sintering method and were found to have the Th3P4 structure. The thermoelectric properties (Seebeck coefficient and electrical resistivity) were measured as a function of temperature and the optimum composition was found for x between 0.2 and 0.3 in which the electrical power factor was a maximum at 1000°C.

Neutron diffraction study of the Th(Co1-xFex)5alloys

We have studied the ordering of Fe atoms and the magnetic properties of Th(Co 1-x Fe x ) 5 alloys with the CaCu 5 - type structure. From the neutron diffraction analysis it is concluded that the larger Fe atoms prefer to occupy the site 3g whereas the smaller Co prefer to occupy the site 2c. The ordering between Fe and Co in these alloys is mainly determined by stearic considerations. The Curie temperatures are found to be sensitive to the type of heat treatment. Although the bulk anisotropy of the alloys up to x \leq 0.7 remains essentially unchanged, the coercivity decreases with increasing iron concentration. The possibility of disordered substitution of a Th atom by a pair of transition metal atoms and its role on the structural and magnetic properties is discussed.

Transport and Magnetic Properties of Th–Np Alloys

The magnetic susceptibilities and electrical resistivities of dilute Th(Np) alloys containing 0.1, 0.5, and 1.0 at.% Np have been measured from below 2°, 59°, 300°K. At the lowest temperatures of the measurements, the resistivities decrease monotonically with temperature, and are proportional to T2. The susceptibilities follow a Curie-Weiss law of the form χ=χ0+C/(T−θ), where θ=−11° and −19° for 0.5% and 1.0% Np, respectively. The Curie-Weiss constant C yields effective moments of 0.8 and 1.1 μβ per Np atom for 0.5% and 1.0% Np. These values are considerably lower than would be expected from the free ionic configuration of 5f46d17s2, and are probably due to hybridization of the 5f electrons, as is the case in pure Np and Pu. The data indicate the formation of a broad 5f virtual bound state at the Fermi level, which then causes paramagnon-conduction electron scattering, as has recently been found for Th(U).1