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International audience; The uranium and plutonium co-conversion process constitutes a continuous subject of interest for MOx fuel fabrication. Among the various routes considered, chemical coprecipitation by the salt effect has been widely investigated regarding its simplicity of integration between the partitioning and purification steps of the PUREX process, and the straightforward recovery of precursors that are easily converted into oxide phases by thermal decomposition. The present study focuses on the coprecipitation behavior of U–Th and U–Pu actinide peroxide mixed systems by examining the precipitation yields and settling properties for nitric acidity in the range of 1 to 3 M and hydrogen peroxide concentration in the range of 4.5 to 7 M. The precipitated solids have been characterized by powder XRD, IR and Raman spectroscopy, laser granulometry and SEM-EDS analyses revealing the synthesis of studtite and actinide(IV) peroxo-nitrates as aggregated particles. The actinide solid phases are uniformly distributed within the filtered cakes. The precursor thermal decomposition results in the formation of oxide phases at low temperature according to a sequential release of water molecules, peroxide ligands and nitrate ions. The calcination step has a limited effect on the morphology of the powders which remain highly divided. The high precipitation rate of actinides makes this chemical route potentially interesting as a co-precipitation process.

The European Mini-Plate Irradiation Experiment (EMPIrE) aims to test the in-pile behavior of various ZrN coated UMo powder batches, produced using different technological processes. UMo(ZrN) particles are typical core-shell systems taking advantages of a dense fissile material, UMo, with a coated ZrN layer acting as a diffusion barrier. The U-7Mo kernels were produced by centrifugal or rotating electrode atomization processes and the ZrN coating was performed by physical vapor deposition or atomic layer deposition processes. A total of ten batches of UMo(ZrN) powders were examined in the as-obtained state, i.e prior to fuel-plate fabrication and before in-pile irradiation. The present investigation gives a characterization of each powder batch mainly in terms of morphological and microstructural features carried out by means of SEM-EDS, LOM, EPMA, AFM and TEM analyses. Digital image processing using ImageJ software was employed to determine several particle size (major axis, minor axis, Feret’s diameters, and equivalent diameter) and shape (aspect ratio, circularity, convexity and concavity) parameters as well as the ZrN deposited layer thickness. The quality of the ZrN layer was examined in terms of surface roughness, grain structure and aggregated habits. Our characterization results draw a detailed portrait of the UMo(ZrN) powders selected for the EMPIrE experiment and allow a classification of the powder batches which is presented as radar chart (Kiviat diagram).

International audience; Nine new ternary uranium transition metal germanides U3TGe5 with T = V, Cr, Mn, Zr, Nb, Mo, Hf, Ta and W have been discovered, in addition to the previously reported compound for T = Ti. These ten intermetallics adopt the anti-CuHf5Sn3-type of structure (hexagonal, P63/mcm, Z = 2). Scanning electron microscopy images, energy dispersive spectroscopy, differential thermal analyses and X-ray data refinements were employed for chemical, thermal and structural characterizations. For the purest samples, obtained for T = Ti, V and Cr, the investigation of the magnetic and transport properties were analyzed revealing the subsequent influence of the 3d metals on the ground-state properties. Ab initio calculations of the band structure of these three U3TGe5 compounds were performed, showing nested Fermi surface which may be associated to the presence of Dirac cones for the magnetically ordered compounds, i.e. for T = Ti and V.

International audience; The phase relations in the binary U-Ga and ternary U-Al-Ga systems were established as an isopleth section and two isothermal sections at 900 K and 1150 K for the whole concentration range, respectively. They were experimentally determined by means of powder and single crystal XRD, SEM-EDS analyses on both as-cast and heat-treated samples and DTA measurements. Both systems were thermodynamically assessed using the Calphad method based on the available data, i.e. phase relations and thermodynamic properties. The new description of the U-Ga phase diagram improves the composition-temperature description for most of invariant reactions. The U-Al-Ga system is characterized by large ternary extensions of the binary phases and the absence of ternary intermediate phase at both 900 K and 1150 K. These experimental results are nicely reproduced by the Calphad assessment, allowing to extract the thermodynamic parameters further used to calculate the liquidus projection and the invariant reactions along with their temperature.

International audience; A novel erbium rich ternary intermetallic compound, Er10Co1+xAl3−x (x = 0.30) has been discovered in the Er–Co–Al ternary system. It crystallizes in a hexagonal ordered variant of the Co2Al5-type in presence of substitutions on two adjacent crystallographic positions. The magnetic behaviour is mainly dominated by an antiferromagnetic ordering observed at TN = 12.7(7) K

A novel gadolinium and cobalt based aluminide, namely Gd3Co4+xAl12−x (x = 0.50(3)) is shown to crystallize in the hexagonal Gd3Ru4Al12 structure-type (space-group P63/mmc, a = 8.6830(1) A, c = 9.3164(2) A at room temperature). The investigation of its magnetic properties revealed a reversible ferromagnetic ordering at TC ≈ 40 K but expanding in a wide temperature range, potentially due to the geometrical magnetic frustrations expected in this structure-type. The magnetocaloric properties of this intermetallic, determined from both magnetization and specific heat data, are dominated by a maximum entropy variation of −3.28 J kg−1 K−1 at 39(1) K and an adiabatic temperature change of about 1.5 K extending from 20 to 40 K, highlighting some interest for low temperature applications.

International audience; The phase relations in the ternary U–Ti–Al system were established for the whole concentration range for two temperatures, 923 K and 1123 K. They were derived from quenched samples annealed at 1123 K for about 500 h and at 923 K for about 720 h using X-ray powder diffraction, scanning electron microscopy and energy dispersive spectroscopic analysis. Only one ternary phase, the Al-rich compound, UTi2Al20, was found. It forms by a peritectic reaction at 1365(5) K, and remains stable at least down to 923 K. Based on single-crystal structure refinements, it was confirmed that it adopts the CeCr2Al20 structure type (cubic, View the MathML sourceFm3¯d, n°227) with lattice parameter at room temperature, a = 14.634(1) Å. Unlike most of the isotypic aluminides, UTi2Al20 should be regarded as a line compound. At 1123 K, the isothermal section is characterized by the extended homogeneity ranges due to mutual exchange between U and Ti and between Ti and Al in the unary phases, whereas at 923 K, the mutual solubility between U and Ti was found null. Regarding the binary phases, only in the Laves phase, UAl2 (cubic-C15, MgCu2-type) such solubilities were observed with limits of about 2 at% of U by Ti and 5.5 at% of Al by Ti, at 1123 K. For the other binary compounds, the solubility of the third component was found negligible at both temperatures.

International audience; Magnetic susceptibility, magnetization, specific heat, electrical resistivity and thermoelectric power of polycrystalline Ce5CoGe2, CeCoGe and CeCo2Ge2 were studied at temperatures down to 2 K and in magnetic fields up to 5 T. The novel phase Ce5CoGe2 was found to be a ferromagnet with the Curie temperature of about 11 K, which exhibits in the paramagnetic region some features of a dense Kondo system with strong crystal field effect. The re-investigated CeCoGe was found to order antiferromagnetically below 4.6 K, while CeCo2Ge2 is an intermediate-valence system, in agreement with previous reports. The thermoelectric power of the latter compound is large (up to 40 μV/K) and positive in the whole temperature range studied, while in the magnetically ordered systems Ce5CoGe2 and CeCoGe it is mostly negative and distinctly smaller (down to −1.5 and −11 μV/K, respectively).

International audience; In the framework of the development of a low 235U enriched nuclear fuel for material testing reactors, γ-U(Mo)/Al based materials are considered as the most interesting prospect. In the process to optimize their composition, addition to both γ-U(Mo) and Al have been proposed. In this paper, the crystallographic composition of Interaction Layers (ILs) in γ-U(Mo,X)/Al and γ-U(Mo,X)/AlSi7 diffusion couples, with X = Cr, Ti, Zr, heat-treated at 600 °C for 2 h, were studied by micro-X-ray diffraction (μ-XRD). When compared to the U(Mo)/Al and U(Mo)/Al(Si) reference systems, all investigated systems involving either Al or Al(Si) as counterparts show interaction products composed of similar phases and related sequences of phase formation. Only relative thicknesses of sub-layers and relative fractions of intermediate phases are correlated with the nature of the X element in the γ-U(Mo,X) alloy. More generally this work shows that γ-U(Mo)/Al and γ-U(Mo)/Al(Si) ILs are now robustly described down to the micrometer scale.

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) A, b = 6.639(1) A and c = 13.702(1) A. 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.

The existence of the binary compounds Th 3 Pt 4 and U 3 Pt 4 has been established in the course of the reinvestigation of the U-Pt and Th-Pt systems. Their structural and physical properties have been studied for the first time. Both compounds solidify from the melt of the elemental components with the stoichiometric ratio. Rietveld refinements reveal that they both adopt the trigonal Pu 3 Pd 4 structure type ( R 3 ¯ space group) with lattice parameters at room temperature of a = 13.6870(3) A, c = 5.7991(2) A for Th 3 Pt 4 and a = 13.2380(2) A, c = 5.6808(2) A for U 3 Pt 4 . Magnetic and specific heat measurements show that Th 3 Pt 4 behaves as a typical metal; it was further used as phonon analogue of the U-counterpart. U 3 Pt 4 undergoes a ferromagnetic ordering below T C = 6.5(5) K. Its low temperature specific heat is dominated by an enhanced Sommerfeld coefficient (246(2) mJ mol U −1 K −2 ) classifying this phase into the heavy fermion family.

The phase relations in the ternary U-Nb-Al system were established for the whole concentration range for 900 K and 1200 K. They were derived from quenched samples annealed at 900 K for three months and at 1200 K for two months by using x-ray powder diffraction, scanning electron microscopy and energy dispersive spectroscopic analyses. The formation of the two ternary phases, UNb 2 Al 20 and U 6 Nb 4 Al 43 was confirmed. Both phases form by peritectic reaction, at 1200(5) K and at 1262(5) K for UNb 2 Al 20 and U 6 Nb 4 Al 43 respectively. Single-crystal structure refinements confirmed that UNb 2 Al 20 adopts the CeCr 2 Al 20 type (cubic, F d 3 ¯ m ) and that U 6 Nb 4 Al 43 crystallizes with the Ho 6 Mo 4 Al 43 type (hexagonal, P 6 3 / mcm ). The isothermal sections are characterized by (i) the extended homogeneity ranges due to mutual exchange between U and Nb and between Nb and Al in the bcc -phases (γU and Nb), at 1200 K, and (ii) a substantial ternary extension with limits of about 6(1) to 10(1) at.% U at 900 K and 1200 K respectively, of the σ-phase (Nb 2 Al, tetragonal, P 4 2 / mnm ). The modeling of these isothermal sections was carried out by the Calphad method. The liquidus projection and the invariant reactions along with their corresponding temperatures were calculated using our optimized database. The electronic properties of both intermediate compounds were measured by means of dc -susceptibility, specific heat and resistivity measurements in the temperature range 2–300 K, revealing for UNb 2 Al 20 enhanced Pauli paramagnetism and complex magnetic features for U 6 Nb 4 Al 43 at low temperature. For the latter compound a composite behavior involving long-and short-range orderings, resulting from intra and inter U dimeric chains along the c -axis is suspected below 12 K.

International audience; The novel intermetallics R3Co4+xAl12-x (R = Tb → Er) crystallize in the hexagonal Gd3Ru4Al12 structure-type where the rare earth atoms form a heavily distorted kagome network. Single crystal X-ray diffraction reveals an unusual 2b substitution site of Co for Al probably driven by steric effects. The four phases order ferromagnetically below 24.0, 17.4, 11.5 and 5.0 K for R = Tb, Dy, Ho and Er, respectively, linearly decreasing with the de Gennes factor of the rare earth. The magnetocaloric properties have been estimated for R = Ho and Er by measuring the magnetization isotherms at various temperatures. The magnetic entropy changes reach maximum values of −12 and −10 J kg−1 K−1 for a magnetic field change from 5 to 0 T. © 2017 Elsevier Ltd

The new compounds U{sub 3}Co{sub 12-x}X{sub 4} with X=Si, Ge were prepared by direct solidification of the corresponding liquid phase, followed by subsequent annealing at 1173 K. Single crystal X-ray diffraction carried out at room temperature showed that they crystallize with the hexagonal space group P6{sub 3}/mmc (no.194) and the unit-cell parameters a=8.130(5), c=8.537(5) A and a=8.256(1), c=8.608(1) A for the silicide and germanide, respectively. Their crystal structure derives from the EuMg{sub 5.2} structure type, and is closely related to the Sc{sub 3}Ni{sub 11}Si{sub 4} and Gd{sub 3}Ru{sub 4-x}Al{sub 12+x} types. For the present compounds, no substitution mechanisms have been observed, the partial occupancy of one Co site results from the presence of vacancies, only. The homogeneity ranges, evaluated by energy dispersive spectroscopy analysis, extend from x=0.0(2) to 0.3(2) and from x=0.0(2) to 1.0(2) for U{sub 3}Co{sub 12-x}Si{sub 4} and U{sub 3}Co{sub 12-x}Ge{sub 4}, respectively. The electronic properties of both compounds were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The U{sub 3}Co{sub 12-x}X{sub 4} compounds are both Pauli paramagnets with their electrical resistivity best described as poor metallic or dirty metallic behavior. - Graphical abstract: The crystal structure of the new compounds U{sub 3}Co{sub 12-x}X{submore » 4}, X=Si, Ge is a ternary ordered variant of the EuMg{sub 5.2}-type with a site preference for the 4e position.« less

The solid state phase equilibria in the Ce–Co–Ge ternary system at 700 °C were investigated by means of X-ray diffraction and scanning electron microscope–energy dispersive X-ray spectroscopy. A total number of nine intermediate phases were characterized and the homogeneity ranges of the various ternary solid solutions of the binary boundary systems (Ce–Co, Ce–Ge and Co–Ge) were studied. The new ternary phase, CeCo 13− x Ge x (4 ≤ x ≤ 4.5) has been discovered. It crystallizes in the tetragonal space group I 4 /mcm (no. 140), with the cell parameters a = 7.974(5) A and c = 11.856(5) A for x = 4. CeCo 9 Ge 4 derives from the CeNi 8.5 Si 4.5 -type, but, with a perfect ordering of the atoms on the crystallographic sites. The phase diagram comprises seven extensions of binaries into the ternary system, eight stoichiometric ternary phases, CeCoGe, CeCo 2 Ge 2 , CeCoGe 3 , Ce 2 Co 3 Ge 5 , Ce 2 CoGe 3 , Ce 3 CoGe 2 , Ce 5 CoGe 2 and Ce 5 Co 4 Ge 13 and two intermediate solid solutions, CeCo 1− x Ge 2 (0 ≤ x ≤ 0.24) and CeCo 13− x Ge x (4 ≤ x ≤ 4.5).

The U3Fe4+xAl12−x (0 < x < 0.5) intermetallic was prepared by arc melting, followed by annealing at 850 °C. This compound crystallizes in the hexagonal Gd3Ru4Al12-type structure (e.g. P63/mmc), with room temperature parameters a = 8.7516(3) A and c = 9.2653(4) A for x = 0. The structure is characterized by planar layers of M3Al4 (M = Gd, U), containing M atoms in a triangular arrangement and forming a distorted Kagome net. Magnetic measurements revealed a spin-glass-type behaviour with a freezing temperature, Tf = 7.9 K. The magnitude of the frequency shift of the freezing temperature is ≈0.03 and a Vogel–Fulcher law is followed with values typical for a spin-glass. 57Fe Mossbauer data show that there is no freezing of the iron magnetic moments directions below Tf, indicating that the origin of the spin-glass-like behaviour is related to topological frustration of the uranium moments.

A systematic study of the U–Fe–Si ternary system was carried out in the whole concentration range, by means of scanning electron microscope observations, associated with energy dispersive X-ray spectroscopy analyses and X-ray powder diffraction measurements performed on as-cast and annealed samples. At 900 °C, the phase diagram is characterized by the existence of nine ternary compounds: U2FeSi3 with the AlB2-type, UFe2Si2 with the ThCr2Si2-type, U3Fe2Si7 with the La3Co2Sn7-type, U2Fe3Si with the MgZn2-type, UFeSi with the TiNiSi-type, U1.2Fe4Si9.7 with the Er1.2Fe4Si9.7-type, U2Fe3Si5 with the Lu2Co3Si5-type, U6Fe16Si7 of the Mg6Cu16Si7-type and UFe5Si3 with its own type of structure. Two intermediate solid solutions, U2Fe17−xSix (3.2

International audience; The phase relations within the U-Al-Ge ternary system were studied for two isothermal sections, at 673 K for the whole Gibbs triangle and at 1173 K for the concentration range 25-100 at% U. The identification of the phases, their composition ranges and stability were determined by x-ray powder diffraction, scanning electron microscopy coupled to energy dispersive spectroscopy and differential thermal analysis. The tie-lines and the solubility domains were determined for the U-Ge and U-Al binaries, the UAl3-UGe3 solid-solution and for the unique ternary intermediate phase U3Al2-xGe3+x. The experimental isopleth section of the pseudo-binary UAl3-UGe3 reveals an isomorphous solid solution based on the Cu3Au-type below the solidus. The U3Al2-xGe3+x solid solution extends for -0.1

The new compounds U6Fe16Si7 and U6Fe16Si7C were prepared by arc-melting and subsequent annealing at 1500 °C. Single-crystal X-ray diffraction showed that they crystallize in the cubic space group Fm 3 ¯ m (No. 225), with unit-cell parameters at room temperature a=11.7206(5) A for U6Fe16Si7 and a=11.7814(2) A for U6Fe16Si7C. Their crystal structures correspond to ordered variants of the Th6Mn23 type. U6Fe16Si7 adopts the Mg6Cu16Si7 structure type, whereas U6Fe16Si7C crystallizes with a novel “filled” quaternary variant. The inserted carbon is located in octahedral cages formed by six U atoms, with U–U interatomic distances of 3.509(1) A. Insertion of carbon in the structure of U6Fe16Si7 has a direct influence on the U–Fe and Fe–Fe interatomic distances. The electronic properties of both compounds were investigated by means of DC susceptibility, electrical resistivity and thermopower. U6Fe16Si7 is a Pauli paramagnet. Its electrical resistivity and thermopower point out that it cannot be classified as a simple metal. The magnetic susceptibility of U6Fe16Si7C is best described over the temperature range 100–300 K by using a modified Curie–Weiss law with an effective magnetic moment of 2.3(2) μB/U, a paramagnetic Weiss temperature, θp=57(2) K and a temperature-independent term χ0=0.057(1) emu/mol. Both the electrical resistivity and thermopower reveal metallic behavior.

The phase equilibria in the ternary Ce-Fe-Si system at 900°C was investigated by means of X-ray diffraction and Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDS). A total number of six ternary compounds were characterized and the homogeneity ranges of the various ternary solid solutions of the binary boundary systems (Ce-Fe, Ce-Si and Fe-Si) were studied. A new ternary phase, Cefe 13-y Si y (3.5

A new ternary compound with stoichiometry U2Co3Al9 has been synthesized. It adopts the orthorhombic Y2Co3Ga9-type structure (space group Cmcm, Z = 4, a = 12.824(2) A, b = 7.515(1) A, c = 9.249(2) A). Measurements of dc- and ac-magnetic susceptibility, electrical resistivity, and magnetoresistivity on polycrystalline samples have been performed. The Curie–Weiss law is strictly followed, with θCW = −48 K and μeff = 3.2 μB. A small kink observed in the temperature dependence of the resistivity is attributed to a phase transition at Tt = 8 K. The magnetoresistivity was found to be negative at all temperatures examined below 45 K, with a sharp minimum at Tt = 8 K.

The isothermal section at 900 °C of the U–Fe–Ge ternary system was assessed using experimental results from X-ray diffraction and observations by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy chemical analysis. The phase diagram at this temperature is characterized by the formation of fourteen stable phases: four homogeneity ranges and ten intermetallic compounds. Among these, there is an extension of the binary compound UFe2 into the ternary system (UFe2−xGex, x

The Ce–Co–Al ternary phase diagram has been reinvestigated at 973 K by means of powder X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and differential thermal analyses. It contains 5 ternary phases (CeCo 2 Al 8 , Ce 2 Co 6 Al 19 , CeCoAl 4 , Ce 3 Co 3 Al 4 and CeCoAl) as well as 7 extensions in the ternary field of pseudo-binaries (CeAl 2 − x Co x with 0 ⩽ x ⩽ 0.18; CeCo 2 − x Al x with 0 ⩽ x ⩽ 0.21; CeCo 3 − y Al y with 0 ⩽ y ⩽ 0.20; Ce 2 Co 7 − x Al x with 0 ⩽ x ⩽ 0.73; Ce 5 Co 19 − y Al y with 0 ⩽ y ⩽ 0.20; CeCo 5 − x Al x with 0 ⩽ x ⩽ 0.71 and Ce 2 Co 17 − y Al y with 0 ⩽ y ⩽ 2.2). Two liquid areas are present at the Al and Ce-rich corners of this isothermal section.

Three new compounds have been found in the U–Pt–Si ternary system, U 3 Pt 23 Si 11 , U 3 Pt 5 Si and U 6 Pt 30 Si 19 . They were prepared by reaction of the elemental components in an arc-melting furnace followed by heat-treatment at 900 °C for several days. Their chemical composition was checked by scanning electron microscopy and by energy dispersive spectroscopy. Their crystal structure was determined by single crystal X-ray diffraction techniques. The compound U 3 Pt 23 Si 11 , formerly reported as U 2 Pt 15 Si 7 , crystallizes in the cubic space group F m 3 ¯ m , with a unit-cell parameter at room temperature, a = 16.8341(3) A. The most striking feature of the structure is the occurrence of octahedral clusters of uranium with short U–U bonds of 3.004(2) A. U 3 Pt 5 Si crystallizes in the orthorhombic space group Imma , in a cell of dimension at room temperature a = 7.1733(3) A, b = 12.9671(6) A and c = 7.3578(3) A. Its crystal structure is closely related to that of Ce 3 Pd 5 Si, from which it only differs by a partial disorder of one Pt-atom site. The dc-magnetic measurement revealed that U 3 Pt 5 Si orders antiferromagnetically at T N = 11(1) K. U 6 Pt 30 Si 19 crystallizes in the hexagonal space group P 6 3 / m , in a cell of dimension at room temperature a = 15.9377(2) A and c = 3.9874(1) A. It belongs to a large family of ternary alloys obeying the general formula, R n ( n + 1 ) T 6 ( n 2 + 1 ) M 4 n 2 + 3 , where R stands for f-metal, T for d-transition metal and M for the main-group element.

The praseodymium cobalt aluminides, PrCo 2 Al 8 and Pr 2 Co 6 Al 19 , were prepared by reaction of the elemental components in an arc-melting furnace, followed by heat treatment at 900 °C for several days. Their chemical composition was checked by scanning electron microscopy and energy dispersive spectroscopy, and their crystal structure was refined from single crystal X-ray diffraction data. PrCo 2 Al 8 adopts the CaCo 2 Al 8 type of structure, crystallizing with the orthorhombic space group Pbam , with four formula units in a cell of dimensions at room temperature: a = 12.4623 ( 3 ) A , b = 14.3700 ( 4 ) A , c = 4.0117 ( 1 ) A . Pr 2 Co 6 Al 19 crystallizes in the monoclinic space group C2/m , with four formula units in a cell of dimensions at room temperature: a = 17.6031 ( 4 ) A , b = 12.1052 ( 4 ) A , c = 8.2399 ( 2 ) A and β = 103.903 ( 1 ) ° . Its structure belongs to the U 2 Co 6 Al 19 type. The crystal structures of both compounds studied can be viewed as three-dimensional structures resulting from the packing of Al polyhedra centred by the transition elements. Along the c -axis, the coordination polyhedra around the Pr atoms pack by face sharing to form strands, which are separated one from another by an extended Co–Al network. Magnetic measurements have revealed that PrCo 2 Al 8 orders antiferromagnetically at T N = 5 K , with a clear metamagnetic transition occurring at a critical field H c =0.9(1) T. The temperature dependence of the susceptibility of Pr 2 Co 6 Al 19 does not provide any evidence for long-range magnetic ordering in the temperature domain 1.7–300 K. At low temperatures ( T μ B and 3.41(2) μ B for PrCo 2 Al 8 and Pr 2 Co 6 Al 19 , respectively. These values are close to the theoretical value of 3.58 μ B expected for a free Pr 3+ ion and exclude any contribution due to the Co atoms. Both compounds exhibit in the temperature range 5–300 K metallic-like electrical conductivity, and their Seebeck coefficient is of the order of several μV/K.

The new compound U 3 Co 4+ x Al 12− x , where x =0.55(2), was prepared by arc-melting of the elemental components, followed by a prolonged annealing at elevated temperature. Scanning electron microscopy-energy-dispersive spectroscopy and powder X-ray diffraction were used to determine the deviation from the ideal stoichiometry. A small homogeneity range, that extends around the composition U 3 Co 4+ x Al 12− x with 0.4(1) ⩽ x ⩽0.7(1), could be detected. Single-crystal diffraction experiments revealed that U 3 Co 4.55 Al 11.45 crystallizes with the Gd 3 Ru 4 Al 12 type-structure, (space group P 6 3 / mmc , Z =2) in a cell of dimensions at room temperature, a =8.6518(2) A, c =9.2620(2) A. The crystal structure can be viewed as an intergrowth of two distinct layers of Co and Al atoms, and U, Al and mixed Al/Co atoms that pile up along the hexagonal axis. The results of the DC magnetization suggest the occurrence of a spin glass state at low temperature ( T f =8 K). The origin of freezing of the magnetic moments may arise from a topological frustration due to the location of the U atoms on the apexes of a distorted Kagome lattice.

Samples with atomic ratios U:Al of 1:3.5 (at.% U:Al=22.2:77.8) and 1:4.5 (at.% U:Al=18.2:81.2) were prepared by standard arc-melting techniques. Two samples were annealed at 600 °C followed by slow cooling to room temperature whereas two other samples were heat-treated at 700 °C over the same period and quenched in ice water. The samples were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray powder diffraction, and single crystal X-ray diffraction experiments. The results show that UAl4 forms as a fully stoichiometric compound without constitutional defect in the U sublattice.

The new compound U2Co6Al19 was prepared by reaction of the elemental components in an arc-melting furnace followed by a heat treatment at 1050°C for 500 h. Its chemical composition was checked by energy-dispersive X-ray analyses and its crystal structure was determined by single crystal X-ray diffraction experiments. It crystallizes with four formula units in the monoclinic space group C2/m in a unit cell of dimensions a=17.4617(3) A, b=12.0474(2) A, c=8.2003(1) A, β=103.915(1)°. The crystal structure of U2Co6Al19 can be regarded as a superstructure of NdCo4−xGa9 structure type. This complex structure consists of a three-dimensional Co–Al framework delimiting tunnels where the U atoms reside. The shortest U–U distances are found in the c direction with alternating values of 3.98(1) and 4.22(1) A. Temperature-dependent magnetization shows a first peak at 12.5 K and a weak ferromagnetic character below the temperature TC=8 K. Magnetization at 1.9 K reaches almost saturation in 5 T with the moment of 0.36 μB/U atom. The complex magnetic behavior of U2Co6Al19 may be ascribed to a canted spin structure resulting from an antiparallel arrangement of the magnetic moments not fully compensated at low temperature. At higher temperature, the compound displays simple paramagnetic behavior.

The two new compounds U 3 Te 5 Ge 0.7 and U 3 Te 5 Sn 0.5 were prepared by heating the binary compound U 3 Te 5 and the corresponding group 14 element at 850°C in a fused-silica tube. Single crystals have been grown by chemical vapor transport using iodine as transporting agent in temperature gradients of 870–840°C and 840–800°C for U 3 Te 5 Ge 0.7 and U 3 Te 5 Sn 0.5 , respectively. They have been characterized by single-crystal X-ray diffraction measurements and by energy dispersive X-ray analysis. The two isostructural compounds crystallize with two formula units in the orthorhombic space group Pmmn in cells of dimensions: U 3 Te 5 Ge 0.7 a =4.2764(1) A, b =13.1029(3) A, c =8.9104(2) A; U 3 Te 5 Sn 0.5 , a =4.3160(1) A, b =13.1999(4) A, c =8.9128(2) A. The crystal structures comprise two independent U atoms with two different coordination geometries. Atom U(1) is surrounded by eight Te atoms in a bicapped trigonal prismatic geometry. Atom U(2) is in a seven coordinate environment of Te atoms, with an arrangement usually described as a 7-octahedron. The three-dimensional packing results in distorted hexagonal cavities where the metalloid atoms are inserted. Magnetic measurements reveal that both compounds U 3 Te 5 Ge 0.7 and U 3 Te 5 Sn 0.5 are hard ferromagnets with ordering temperature of 135 and 140 K, respectively. At low temperature, they display large magnetocrystalline anisotropy with origin on the domain wall pinning at the magnetic domain boundaries.

The binary uranium tellurides U 3 Te 5 and U 2 Te 3 have been studied by neutron powder diffraction as a function of temperature. In the case of U 3 Te 5 ( Pnma space group), the magnetic moments of the three uranium sites (U 1 , U 2 , U 3 ) are lying in the a – c plane with a F x C z -type structure, with different magnetic moments for U 1 , U 2 , U 3 . A spin reorientation towards the c direction occurs around T =45 K. Neutron diffraction data for U 2 Te 3 ( Pnma space group) are consistent with an antiferromagnetic G x A z -type structure. The magnetic moments of uranium atoms in two crystallographic sites (U 1 , U 2 ) are in the a – c plane with different magnetic moments for U 1 and U 2 . A slight spin reorientation on the U 2 site occurs around T =45 K. Close to the ordering temperature, hints of a complex magnetic structure can be detected. In both compounds, these results are correlated with the macroscopic magnetic measurements.

The new compounds La{sub 4}Ti{sub 2}O{sub 4}Se{sub 5} and La{sub 6}Ti{sub 3}O{sub 5}Se{sub 9} have been obtained from stoichiometric reactions of La, Ti, TiO{sub 2}, and Se in fused-silica tubes at 1223 K. Potassium halide fluxes were used to promote the crystallization. The compounds have been characterized by single-crystal X-ray diffraction methods. La{sub 4}Ti{sub 2}O{sub 4}Se{sub 5} crystallizes in the orthorhombic space group Cmcm with eight formula units in a cell at 153 K of dimensions a=3.9695(4) {angstrom}, b=33.115(3) {angstrom}, c=18.6380(18) {angstrom}. The five independent La atoms in the structure are found in four different coordination polyhedra, namely tricapped trigonal prism, bicapped trigonal prism, square antiprism, and 7-octahedron, whereas the three independent Ti atoms have octahedral coordination. The crystal structure comprises infinite layers that stack along the b-axis. Two adjacent layers are linked by La-Se bonds. La{sub 4}Ti{sub 2}O{sub 4}Se{sub 5} represents the first rare-earth titanium oxychalcogenide containing only Ti{sup 3+} cations. La{sub 6}Ti{sub 3}O{sub 5}Se{sub 9} crystallizes in the monoclinic space group C2/m with four formula units in a cell at 153 K of dimensions a=43.999(6) {angstrom}, b=3.9454(6) {angstrom}, c=11.1093(16) {angstrom}, {beta}=96.882(2){degree}. The six independent La atoms in the structure are found in three different coordination polyhedra, namely tricappedmore » trigonal prism, bicapped trigonal prism, and 7-octahedron. The four independent Ti atoms have octahedral coordination. The crystal structure comprises infinite condensed layers of composition {sub {infinity}}{sup 2}[La{sub 2}Ti{sub 1}O{sub 2}Se{sub 3}] that stack successively with extended slabs of composition {sub {infinity}}{sup 2}[La{sub 4}Ti{sub 2}O{sub 3}Se{sub 6}] along the a-axis. La{sub 6}Ti{sub 3}O{sub 5}Se{sub 9} is a mixed-valence compound in which two-thirds of the Ti cations are Ti{sup 3+} and one-third are Ti{sup 4+}.« less

The new compounds Ln 7 VO 4 Se 8 ( Ln =Nd, Sm, Gd) were each prepared by heating V, Se, and the corresponding rare-earth sesquioxide at 1223 K in a sealed fused-silica tube. Single crystals have been grown through the use of an antimony flux. They have been characterized by single-crystal and powder X-ray diffraction measurements and by energy dispersive X-ray analysis. These isostructural compounds crystallize with two formula units in the orthorhombic space group Pbam in cells (at 153 K) of dimensions: Nd 7 VO 4 Se 8 , a =14.3419(9) A, b =15.5528(10) A, c =3.9948(3) A; Sm 7 VO 4 Se 8 , a =14.200(2) A, b =15.451(2) A, c =3.9511(6) A; Gd 7 VO 4 Se 8 , a =14.075(8) A, b =15.424(6) A, c =3.903(1) A. The new structure type comprises four crystallographically independent Ln atoms with three different coordination geometries and one V atom in an octahedral environment. Magnetic measurements reveal that Gd 7 VO 4 Se 8 is paramagnetic down to 5 K.

Thermoelectric properties have been studied on ternary compounds from the U-Fe-Si system in term of resistivity and thermopower. Electrical resistivity measurements were carried out in the range 18-300 K for all samples. The thermoelectric power was measured with a thermal gradient of 1 K. Results for U 3 Fe 2 Si 7 , U 2 FeSi 3 , U 1.2 Fe 4 Si 9.7 , U 2 Fe 3 Si 5 and UFe 2 Si 2 are shown in this paper.

The crystal structure of the binary uranium telluride U{sub 3}Te{sub 5} has been determined for the first time from single-crystal X-ray diffraction data. This compound crystallizes with a new structure type, in the orthorhombic space group Pnma (No. 62), with the unit cell parameters a = 16.098(7) {angstrom}, b = 4.210(2) {angstrom}, c = 14.060(4) {angstrom}, Z = 4. The structure has been refined to an agreement index of R(F) = 0.049 and R{sub w}(F) = 0.050 for 50 variables and 1322 observations [I > 3{sigma}(I)]. The three nonequivalent uranium atoms are coordinated to eight tellurium atoms in bicapped trigonal prismatic arrangements. These prisms are stacked along the b axis by sharing their triangular faces and are linked by edge sharing to form a 6-fold capped triprism which is the repeating building unit of the structure. Magnetic measurements reveal ferromagnetic behavior below {approx}120 K with a significant spin reorientation around 45 K. In the paramagnetic region U{sub 3}Te{sub 5} follows a modified Curie-Weiss law with an effective magnetic moment of 2.69 {mu}{sub B}/U atom and {chi}{sub 0} = 3.0316 {times} 10{sup {minus}3} emu/mol.

The new ternary phase U 34 Fe 4− x Ge 33 has been synthesized and characterized by means of single crystal X-ray diffraction, magnetization, Mossbauer spectroscopy, specific heat, electrical resistivity, magnetoresistivity and thermopower measurements. It crystallizes in its own tetragonal structure type which can be described as derived from the one of the binary USi (U 34 Si 34.5 structure-type, space group I 4/ mmm ), with lattice parameters at room temperature, a = 10.873(5) A and c = 25.274(3) A. Structure refinement confirmed six inequivalent U atoms, occupying sites with dissimilar coordination, the Ge atoms staying on seven positions and Fe on two positions, one of the Fe sites with a partial occupancy. The U sub-lattice is composed by the stacking of a square cupola, two distorted cubes and a square orthobicupola. U 34 Fe 4− x Ge 33 with x = 0.68 undergoes a ferromagnetic-type transition below 28 K. Mossbauer spectroscopy shows that the magnetism is ruled by the U sub-lattice, as Fe atoms have no ordered moments. The Sommerfeld coefficient of the electronic specific heat is γ = 131 mJ/(mol U K 2 ), whereas the estimated magnetic entropy at T C is 0.22 R ln2. A residual resistivity of 314 μΩ cm and a resistivity ratio of 1.1 were found in the electrical resistivity curve, which also exhibits an upturn below T C that shifts towards higher temperatures with the applied magnetic field. This behavior may be related to some disorder in the non-magnetic lattice and/or partial ordering of the magnetic lattice.

Single crystal X-ray studies of U2Te5 revealed that this compound crystallizes in the monoclinic system with a = 34.42(2) A , b = 4.181(1) A , c = 6.074(3) A , β = 95.43(3)°. The crystal structure was solved in the C2/m space group and refined to final values of reliability factors R(F) = 0.031 and Rω(F) = 0.038, corroborating other recent results. The two crystallographically independent uranium atoms are coordinated to eight tellurium atoms in a bicapped trigonal prismatic geometry. The layered structure is built up from stacking along the a-direction of UTe2 slabs separated by Van der Waals gaps. Magnetic measurements reveal that U2Te5 exhibits paramagnetic behaviour down to 2K, and electrical resistivity measurements on a single crystal indicate semiconducting behaviour.

Phase relations in the Er–Cu–Ga ternary system have been established at 973 K by means of powder X-ray diffraction complemented by energy dispersive spectroscopy coupled to scanning electron microscopy. The isothermal section of the phase diagram comprises eight extensions of binaries into the ternary system, ErCu 1− x Ga x ( x ≤ 0.5), ErCu 2− x Ga x ( x ≤ 1.1), ErCu 5− x Ga x ( x ≤ 0.5), Er 5 Cu x Ga 3− x ( x ≤ 0.60), Er 3 Cu x Ga 2− x ( x ≤ 0.24), ErCu x Ga 1− x ( x ≤ 0.10), ErCu x Ga 2− x ( x ≤ 0.30) and ErCu x Ga 3− x ( x ≤ 0.35), as well as six ternary intermediate phases, ErCu x Ga 2− x (0.4 ≤ x ≤ 0.7), Er 14 Cu 51− x Ga x (5.5 ≤ x ≤ 11.0), ErCu 5− x Ga x (0.8 ≤ x ≤ 2.3), Er 2 Cu 17− x Ga x (4.9 ≤ x ≤ 8.0), ErCu 12− x Ga x (5.7 ≤ x ≤ 6.7) and Er 3 Cu x Ga 11− x (1.5 ≤ x ≤ 4.4), all deriving from binary structure-types.

Magnetic susceptibility, magnetization, electrical resistivity and thermoelectric power of polycrystalline Ce 2 CoGe 3 , Ce 3 CoGe 2 , CeCo 0.86 Ge 2 , Ce 5 Co 4 Ge 13 , CeCoGe 3 , and Ce 2 Co 3 Ge 5 were studied in wide temperature and magnetic field ranges. The results of magnetic properties and electrical resistivity measurements carried out for Ce 3 CoGe 2 , CeCo 0.86 Ge 2 , CeCoGe 3 and Ce 2 Co 3 Ge 5 corroborate the data reported in literature. Ce 2 CoGe 3 and Ce 5 Co 4 Ge 13 were found to be ferromagnetically ordered below 10 and 7 K, respectively. Moreover, the resistivity of Ce 2 CoGe 3 shows Kondo-like behavior. The thermoelectric power exhibits in all six phases a large broad maximum, located between 50 and 150 K, most likely due to the presence of 4 f electrons.

A new ternary compound, U 9 Fe 7 Ge 24 , was synthesized by arc-melting the elements, followed by annealing at 900 °C. This compound was characterized by single crystal and powder X-ray diffraction, magnetization, specific heat and electrical transport measurements. It crystallizes in an original tetragonal structure type (space group I4/mmm ), with lattice parameters a = 12.3789(2) A and c = 18.2881(3) A. Three uranium, eighth germanium, and three iron crystallographic sites exist in this structure, with the atoms making a stacking of infinite chains along the a and b axis. From their interatomic distances strong interactions between the uranium and germanium atoms can be predicted. The magnetic and specific heat measurements down to 2 K do not show any magnetic transition. The Curie–Weiss behaviour with a negative paramagnetic Curie temperature θ p = −94 K and reduced effective magnetic moment of μ eff = 2.13 μ B /U indicate that the compound is rather far from onset of magnetism, presumably due to a strong hybridisation of the 5 f and ligand states. The electrical transport measurements show a metallic behaviour.

International audience; We report on the existence in the Uâ€"Ruâ€"Al system of a novel compound, URu2Al10, crystallizing in the orthorhombic YbFe2Al10-type structure, where the uranium atoms are caged in Ruâ€"Al polyhedra, forming a clathrate-like structure. Results of the magnetic susceptibility, electrical resistivity in zero and in magnetic fields up to 8 T, thermopower and specific heat, performed in a wide temperature range, are presented. No magnetically ordered state down to the lowest temperature measured has been found. On the basis of (i) the susceptibility anomaly occurring at about 50 K and (ii) the positive magnetoresistivity, growing with applied magnetic field as αBn (n ≈ 3/2), (iii) a characteristic temperature variation of the thermopower, as well as (iv) a moderate value of the Sommerfeld coefficient, a mixed-valence state of uranium in this compound has been postulated. This points to similarities between the presently studied compound and the behaviour of other Ru-containing uranium ternaries, such as U2Ru2Sn and U2RuGa8, classified earlier as valence-fluctuating type materials.

International audience; The new ternary compounds U2Co3Ge and U6Co12Ge4 have been discovered during the investigation of the U-Co-Ge system. The Laves phase, U2Co3Ge crystallizes in the hexagonal Mg2Cu3Si type structure (P63/mmc) with the lattice parameters a = 5.203(1) Å and c = 7.687(1) Å. U6Co12Ge4 and its carbon-inserted derivative U6Co12Ge4C, crystallize, at room temperature in cubic unit cells, which derive from the Ca3Ag8 type structure (View the MathML source space group) with the lattice parameter a = 8.690(1) Å and a = 8.740(1) Å, respectively. An interesting feature of their crystal structure is the formation of [U6] octahedra, which can be either empty or occupied by light elements such as O, N, or C. Measurements of the physical properties revealed that U2Co3Ge and U6Co12Ge4 are Pauli paramagnets with metallic character of their electrical conductivity. In turn, U6Co12Ge4C showed Curie-Weiss paramagnetism with an effective magnetic moment of 2.3(1)μB per U atom.

International audience; The ternary antimonides Ln3Pd8Sb4 (Ln=Y, Gd, Tb, Dy, Ho, Er, Tm) have been synthesized for the first time. The crystal structure of Er3Pd8Sb4 has been solved from the X-ray single crystal data: own type structure, space group Fm3¯m, a=1.3050(1) nm, RF=0.0484, RW=0.0524 for 17 free parameters and 401 reflections with F(hkl)>4σ(F). The structure of Er3Pd8Sb4 can be viewed as a ternary ordered version of the Sc11Ir4-type. The lattice parameters of the isotypic compounds Ln3Pd8Sb4 (Ln=Y, Gd, Tb, Dy, Ho, Tm) have been refined from the X-ray powder diffraction data. The magnetic and electrical properties of the compounds Ln3Pd8Sb4 (Ln=Tb, Ho, Er) have been studied down to 1.75 K. The Ho- and Er-based phases have been found to order antiferromagnetically at 2.5 and 2.0 K, respectively. For all three compounds, the magnetic susceptibility follows in the paramagnetic region the Curie-Weiss behavior with the effective magnetic moments close to the respective free trivalent ion values. All three antimonides studied exhibit metallic character of the electrical conductivity.

Two novel ternary intermediate phases, namely URuSi 3− x ( x =0.11) and U 3 Ru 2 Si 7 were found in the Si-rich part of the U – Ru – Si phase diagram. Single crystal X-ray diffraction measurements, carried out at room temperature, indicated that URuSi 3− x crystallizes in its own tetragonal type structure (space group P 4/ nmm , no. 129; unit cell parameters: a =12.108(1) A and c =9.810(1) A), being a derivative of the BaNiSn 3 -type structure. U 3 Ru 2 Si 7 adopts in turn a disordered orthorhombic La 3 Co 2 Sn 7 -type structure (space group Cmmm , no. 65; unit cell parameters: a =4.063(1) A, b =24.972(2) A and c =4.072(1) A). As revealed by magnetization, electrical resistivity and specific heat measurements, both compounds order magnetically at low temperatures. Namely URuSi 3− x is a ferromagnet with T C =45 K, and U 3 Ru 2 Si 7 shows ferrimagnetic behavior below T C =29 K.

Physico-chemical analysis techniques, including X-ray diffraction and Scanning Electron Microscope–Energy Dispersive X-ray Spectroscopy, were employed to construct the isothermal section of the Er–Fe–Al system at 800 °C. At this temperature, the phase diagram is characterized by the formation of five intermediate phases, ErFe 12− x Al x with 5 ≤ x ≤ 8 (ThMn 12 -type), ErFe 1+ x Al 1− x with −0.2 ≤ x ≤ 0.75 (MgZn 2 -type), ErFe 3− x Al x with 0.5 x ≤ 1 (DyFe 2 Al-type), Er 2 Fe 17− x Al x with 4.74 ≤ x ≤ 5.7 (TbCu 7 -type) and Er 2 Fe 17− x Al x with 5.7 x ≤ 9.5 (Th 2 Zn 17 -type), seven extensions of binaries into the ternary system; ErFe x Al 3− x with x 3 Cu-type), ErFe x Al 2− x with x ≤ 0.68 (MgCu 2 -type), Er 2 Fe x Al 1− x with x ≤ 0.25 (Co 2 Si-type), ErFe 2− x Al x with x ≤ 0.5 (MgCu 2 -type), ErFe 3− x Al x with x ≤ 0.5 (Be 3 Nb-type), Er 6 Fe 23− x Al x with x ≤ 8 (Th 6 Mn 23 -type), and Er 2 Fe 17− x Al x with x ≤ 4.75 (Th 2 Ni 17 -type) and one intermetallic compound; the ErFe 2 Al 10 (YbFe 2 Al 10 -type).

International audience; The solidification paths for UFeB4, UFe3B2 and UFe4B, ternary compounds, situated along the U:(Fe,B) = 1:5 line in the B-Fe-U phase diagram, are proposed based on x-ray powder diffraction measurements, differential thermal analysis, heating curves and scanning electron microscopy observations complemented with energy and wavelength dispersive x-ray spectroscopies. The compounds melt incongruently and are formed by peritectic reactions. The present work demonstrates the existence of a cascade of peritectic reactions along the U:(Fe,B) = 1:5 composition line, establishes peritectic temperatures and proposes an isopleth diagram along this line

Three new ternary gallides have been found in the Er–Cu–Ga ternary system. Their crystal structure, as well as that of the previously reported ErCu 0.5 Ga 1.5 , has been refined from single crystal X-ray diffraction data. ErCu 2− x Ga x (0.4 ≤ x ≤ 0.7) crystallizes in the CaIn 2 structure-type (space group P 6 3 / mmc ), ErCu 5− x Ga x (0.8 ≤ x ≤ 2.3) in the CaCu 5 -type (space group P 6/ mmm ), ErCu 12− x Ga x (5.7 ≤ x ≤ 6.7) in the ThMn 12 -type (space group I 4/ mmm ) and Er 14 Cu 51− x Ga x (5.5 ≤ x ≤ 11.0) in the Gd 14 Ag 51 -type (space group P 6/ m ). Magnetic measurements show Curie–Weiss paramagnetic behavior down to 2 K for these four phases.

International audience; Abstract Experimental results on dc and ac susceptibility, magnetization and magnetic relaxation, specific heat, electrical resistivity and magnetoresistivity up to 8 T are reported for the novel ternary uranium aluminide U3Co4.55Al11.45. The temperature dependence of the dc susceptibility shows a cusp at a characteristic temperature Tf = 8-10 K that depends weakly on the applied magnetic field. The observed pronounced difference between the ZFC and FC magnetization, as well as the decay in the remanence both give evidence that a highly irreversible, frozen state is formed below Tf which is reminiscent of spin-glass behaviour. The real and imaginary parts of the ac-susceptibility show the corresponding Tf peaks being only slightly dependent on frequency. Electrical resistivity measured at zero and in fields up to 8 T indicates that the Kondo-like state becomes dominant at temperatures above Tf.