Chemical bonding in the UFe1-xNixAl alloys

Journal of Electronic Materials, 2017

Cubic uranium compounds such as UX 3 (X is a non-transition element of groups IIIA or IVA) exhibit highly diverse magnetic properties, including Pauli paramagnetism, spin fluctuation and anti-ferromagnetism. In the present paper, we explore the structural, electronic and magnetic properties as well as the hyperfine fields (HFFs) and electric field gradients (EFGs) with quadrupole coupling constant of UX 3 (X = In, Tl, Pb) compounds using local density approximation, Perdew-Burke-Ernzerhof parametrization of generalized gradient approximation (PBE-GGA) including the Hubbard U parameter (GGA + U), a revised version of PBE-GGA that improves equilibrium properties of densely packed solids and their surfaces (PBEsol-GGA), and a hybrid functional (HF-PBEsol). The spin orbit-coupling calculations have been added to investigate the relativistic effect of electrons in these materials. The comparison between the experimental parameters and our calculated structural parameters we confirm the consistency and effectiveness of our theoretical tools. The computed magnetic moments show that magnetic moment increases from indium to lead in the UX 3 family, and all these compounds are antiferromagnetic in nature. The EFGs and HFFs, as well as the quadrupole coupling constant of UX 3 (X = In, Tl, Pb), are discussed in detail. These properties primarily originate from f and p states of uranium and post-transition sites.

Journal of Alloys and Compounds, 2006

The crystallographic and electronic structure of UFe 2 Al 10 was studied as a function of pressure by combining X-ray diffraction results with the full potential linearized augmented plane wave (LAPW) calculations method. The volume-pressure reduction measured at 23.5 GPa is V/V 0 = 0.87, with a B 0 value of 132 ± 8 GPa. The uranium 5f electrons in this compound are located in a narrow and well-defined band above E Fermi , having a very weak interaction with the iron 3d band located below E Fermi . Consequently, the DOS at E Fermi is close to zero, indicating a close to zero-magnetic moment of the uranium atom at low temperature up to a pressure of 23.5 GPa, as expected from the layered crystallographic structure of this compound. The above assumption is supported by preliminary neutron diffraction data, where no long-range magnetic order was detected down to 3 K.

Journal of the Less Common Metals, 1985

The magnetic properties of uranium-3d Laves phases UFez, UCoz, UN& can be understood in terms of a simple band model, which assumes that the 3d band is situated below the 5f band i.n uranium. The electronic transfer towards the 3d band results in an almost total depopulation of the 5f band in the case of UFe2 with a magnetic moment predominantly of 3d origin. The influence of substitution of iron by several percent of titanium in UFez (the solubility limit of 8% was observed) is studied in this paper. A considerable increase in T, and a slight enhancement of the spontaneous moment per Fe atom with increasing titanium concentration was observed. These changes are tentatively attributed to the increasing localization of 3d electrons on the assumption that the Ti 3d states are situated above E, in U(Fei-XTi,)2 compounds.

Journal of Nuclear Materials, 2011

The ground-state properties of U-Mo solid solutions are studied by density functional theory and compared to the similar U-Zr system. We discuss how the heat of formation in both alloys correlates with the charge transfer between the alloy components, and how the specific behavior of the density of states in the vicinity of the Fermi level promotes the stabilization of the U 2 Mo compound. Our calculations suggest that, due to the existence of a single c-phase over the typical fuel operation temperatures, c-U-Mo alloys should indeed have much lower constituent redistribution than c-U-Zr alloys for which binodal decomposition causes a high degree of constituent redistribution.

Journal of Magnetism and Magnetic Materials, 2017

Crystal structure, magnetization, and specific heat were studied on single crystal of uranium intermetallic compound UOsAl. It is a hexagonal Laves phase of MgZn 2 type, space group P6 3 /mmc, with lattice parameters a=536.4 pm, c=845.3 pm. Shortest inter-uranium distance 313 pm (along the c-axis) is considerably smaller than the Hill limit (340 pm). The compound is a weakly temperature-dependent paramagnet with magnetic susceptibility of ≈1.5*10 −8 m 3 mol −1 (at T=2 K), which is slightly higher with magnetic field along the a-axis compared to the c-axis. The Sommerfeld coefficient of electronic specific heat has moderate value of γ=36 mJ mol −1 K −2 .

Journal of Magnetism and Magnetic Materials, 2014

Based on DFT calculations, hydrogen insertion in U 2 Ti intermetallic with AlB 2-type structure leading to U 2 TiH 3 with sites identified from energy discrimination between different hypotheses is found to decrease the cohesive energy through weakening of the Ti-U bonds, to expand the lattice along c hexagonal axis due to strong U-U in-plane bonding and to induce iono-covalent character with H-0.65. The anisotropic volume expansion involves a strong localization of out-of-plane uranium f z 3-3zr 2 orbitals leading to developing a magnetic moment on uranium in a predicted ferromagnetic ground state, oppositely to non magnetic intermetallic.

Surface Science, 2002

We present a comparative study of UNi 2 and UNi 5 intermetallic compounds and U-Ni thin films prepared by sputter deposition. The aim of this work was to study the electronic structure of the U-Ni alloys, and in particular to investigate to what extent thin films are representative of the corresponding bulk materials. Electronic structure and surface composition was investigated by X-ray and ultraviolet photoelectron spectroscopies respectively, and X-ray induced Auger electron spectroscopy. The composition of thin films, sputter deposited from a UNi 5 target, was strongly dependent on deposition conditions (pressure, target voltage), and ranged from U 20 Ni 80 to U 14 Ni 86. Deposition at room temperature resulted in amorphous films, while deposition at a substrate temperature of 473 K lead to the formation of crystalline phases. In all phases, the U 5f electrons are itinerant and remain pinned at the Fermi-level. With increasing U content, the Ni 3d band shifts towards higher binding energies and becomes narrower than in elemental Ni.

Journal of Alloys and Compounds, 2008

The new ternary compound U 3 Fe 4 Ge 4 was prepared by melting the pure metals in the stoichiometric ratio. An ingot of large scale domain was obtained by decreasing the temperature from the liquid state down to 1000°C over 4 h. Single crystal X-ray diffraction revealed that U 3 Fe 4 Ge 4 crystallizes with the Gd 3 Cu 4 Ge 4-type of structure, in the orthorhombic space group Immm (no. 71), Z = 2, with unit-cell parameters at room temperature of, a = 4.090(1) Å, b = 6.639(1) Å and c = 13.702(1) Å. The crystal structure is characterized by two U, one Fe and two Ge independent crystallographic positions and can be described as resulting from the condensation by face-sharing and edge-sharing of U(1)Ge6 octahedrons, U(2)Ge6 trigonal prisms and Fe(1)Ge4 tetrahedrons. The electronic properties of this new compound were investigated by means of electrical resistivity, thermopower, ac and dc magnetic susceptibility and 57 Fe Mossbauer spectroscopy. U 3 Fe 4 Ge 4 undergoes a ferromagnetic transition below T C = 17(1) K. The low temperature (4 K) 57 Fe Mossbauer spectra can be well fitted using a model with Fe atoms in a paramagnetic state, suggesting that the magnetic ordering originates from the U sublattice alone.

Materials Letters, 1994

The U-Fe-M (M= Al, Si) phase diagrams were investigated around UFe12_-xMx compositions by SEM/EDS in order to detect intermetallic congruent melting compounds with ThMn,,-type structure. Single crystals with UFel,_,& (6.26~~ 8.2) and UFe&i,.s compositions, both with ThMn,,-type structure, were grown from the melt using the Czochralski method.

Hyperfine Interactions, 1987

In the pseudo-binary alloy system U(Fe. Co)~, 9. .-X Z the ordering transition temperature andt t~ae ~7agnetic moment decrease rapidly with x. Fe M~Sssbauer measurements on the alloys (x = 0.08 and 0.20) have been performed as a function of t~perature. The observed hyperfine field at the Fe nucleus is much reduced with respect to that in UFe 2. I.

Inorganic Chemistry, 2010

Black prisms of UFeS 3 and UFeSe 3 have been synthesized by solid-state reactions of U, Fe, and S or Se with CsCl as a flux at 1173 K. The structure of these isostructural compounds consists of layers of edge-and corner-sharing FeS 6 or FeSe 6 octahedra that are separated by layers of face-and edge-sharing US 8 or USe 8 bicapped trigonal prisms. The isomer shifts in the iron-57 M € ossbauer spectra of both UFeS 3 and UFeSe 3 are consistent with the presence of highspin iron(II) ions octahedrally coordinated to S or Se. The XANES spectra of UFeS 3 and UFeSe 3 are consistent with uranium(IV). Single-crystal magnetic susceptibility measurements along the three crystallographic axes of UFeSe 3 reveal a substantial magnetic anisotropy with a change of easy axis from the a-axis above 40 K to the b-axis below 40 K, a change that results from competition between the iron(II) and uranium(IV) anisotropies. The temperature dependence of the magnetic susceptibility along the three axes is characteristic of two-dimensional magnetism. A small shoulder-like anomaly is observed in the magnetic susceptibilities along the aand b-axes at 96 and 107 K, respectively. Below 107 K, the iron-57 M€ ossbauer spectra of UFeS 3 and UFeSe 3 show that the iron nuclei experience a magnetic hyperfine field that results from long-range magnetic ordering of at least the iron(II) magnetic moments because the field exhibits Brillouin-like behavior. Below 40 K there is no significant change in the M € ossbauer spectra as a result of change in magnetic anisotropy. The complexity of the iron-57 M € ossbauer spectra and the temperature and field dependencies of the magnetic properties point toward a complex long-range magnetic structure of two independent iron(II) and uranium(IV) two-dimensional sublattices. The temperature dependence of the single-crystal resistivity of UFeSe 3 measured along the a-axis reveals semiconducting behavior between 30 and 300 K with an energy gap of about 0.03 eV below the 53 K maximum in susceptibility, of about 0.05 eV between 50 and 107 K, and of 0.03 eV above 107 K; a negative magnetoresistance was observed below 60 K.

Journal of Alloys and Compounds, 2008

The atomic structure of a new ternary U 2 FeAl 20 phase appearing in the Al-rich corner of a U-Fe-Al system was solved using electron crystallography and X-ray powder diffraction techniques (XRD). The positions of U atoms were determined from crystallographically processed high-resolution electron microscopy (HRTEM) images. These positions were used as a starting set for determining the coordinates of Fe and Al atoms by difference-Fourier synthesis technique. The U 2 FeAl 20 phase is tetragonal and belongs to the I42m space group. Its unit cell contains 80 Al, 4 Fe, and 8 U atoms. The lattice parameters obtained after Rietveld refinement are: a = 12.4138Å, c = 10.3014Å. The reliability factors characterizing the Rietveld refinement procedure are: R p = 8.65%, R wp = 11.2% and R b = 5.93%.

Journal of Materials Chemistry, 1996

Heat capacity experiments, crystal structure determination and transmission electron microscopy have been carried out on U 3 Cu 3 Sn 4 single-crystals. U 3 Cu 3 Sn 4 was confirmed to be a heavy-fermion antiferromagnet (T N = 13(1) K) with a low temperature electronic heat capacity coefficient γ = 390 mJ/mol U K 2 . Low temperature heat capacity experiments on a U 3 Ni 3 Sn 4 singlecrystal indicate that below 0.4 K there is a crossover between the previously observed non-Fermi liquid behavior and a Fermi liquid state.

Journal of Alloys and Compounds, 2002

Journal of Alloys and Compounds, 2012

Several U-based intermetallic compounds (UCoGe, UNiGe with the TiNiSi structure type and UNiAl with the ZrNiAl structure type) and their hydrides were studied from the point of view of compressibility and thermal expansion. Confronted with existing data for the compounds with the ZrNiAl structure type a common pattern emerges. The direction of the U-U bonds with participation of the 5f states is distinctly the "soft" crystallographic direction, exhibiting also the highest coefficient of linear thermal expansion. The finding leads to an apparent paradox: the closer the U atoms are together in a particular direction the better they can be additionally compressed together by applied hydrostatic pressure.