O. Tougait

Evidence for the presence of U–Mo–Al ternary compounds in the U–Mo/Al interaction layer grown by thermal annealing: a coupled micro X-ray diffraction and micro X-ray absorption spectroscopy study

The systematic presence of the ternary phases U6Mo4Al43 and UMo2Al20 is reported in a U–Mo/Al interaction layer grown by thermal annealing. This work shows, therefore, the low Mo solubility in UAl3 and UAl4 binary phases; it contradicts the hypothesis of the formation of (U,Mo)Al3 and (U,Mo)Al4 solid solutions often admitted in the literature. Using µ-XAS (micro X-ray absorption spectroscopy) at the Mo K edge and µ-XRD (micro X-ray diffraction), the heterogeneity of the interaction layer obtained on a γ-U0.85Mo0.15/Al diffusion couple has been precisely investigated. The UMo2Al20 phase has been identified at the closest location from the Al side. Moreover, µ-XRD mapping performed on an annealed fuel plate enabled the characterization of the four phases resulting from the γ-U0.85Mo0.15/Al and (U2Mo + α-U)/Al interactions. A strong correlation between the concentrations of UAl4 and UMo2Al20 and those of UAl3 and U6Mo4Al43 has been shown.

Isothermal section at 750°C of the U–Fe–Sn ternary system

A systematic investigation of the isothermal section at 850 8C of the U–Fe–Al ternary system was done by means of scanning electron microprobe analysis and X-ray powder diffraction. At this temperature the phase diagram is characterized by the formation of seven ternary phases and two extended ranges of solubility. Three compounds form with non-existing, or negligible, homogeneity domains: UFe2Al10 (YbFe2Al10-type, aZ8.9146(3) A u , bZ10.1986(3) A u , cZ9.0114(3) A u ); U2Fe3.6Al13.4 (Th2Ni17-type, aZ8.8589(2) A u , cZ8.9824(2) A u ); and U2Fe12Al5 (Th2Ni17-type, aZ8.5631(7) A u , cZ8.438(1) A u ). Four other phases exhibit more or less extended homogeneity ranges: UFe1CxAl1Kx (MgZn2-type); U3Fe4CxAl12Kx (Gd3Ru4Al12-type); U2Fe17KxAlx (Th2Zn17-type); and UFexAl12Kx (ThMn12-type). The two extended solid solutions, UAl2KxFex and UFe2KxAlx, are formed from the UAl2 and UFe2 binary compounds, respectively, both crystallizing in the cubic MgCu2-type structure. q 2004 Elsevier Ltd. All rights reserved.

Synthesis, crystal structure and magnetic properties of a new ternary uranium telluride : Tl0.56UTe3

Abstract The new ternary uranium telluride Tl0.56UTe3 crystallizes in the orthorhombic system ( a = 4.212(2) A , b = 23.287(7) A , c = 6.091(3) A ), space group Cmcm. The structure was solved from X-ray diffraction data collected from a single crystal grown by the chemical vapor transport method. The structure of Tl0.5656UTe3 is built up from [UTe3] layers separated by Tl planes, with a partial occupation of the Tl sites. Magnetic measurements show that Tl0.56UTe3 is paramagnetic down to 2 K.

Crystal structure and magnetic properties of the diuranium tritelluride U2Te3

Abstract Single crystals of U 2 Te 3 were obtained by solid state reaction between the elements in stoichiometric proportions mixed with a small quantity of cesium chloride. U 2 Te 3 crystallizes in the orthorhombic system, space group Pnma (n o 62), with unit cell parameters a = 12.175(2)A, b = 4.370(1)A, c = 11.828(2)A, and Z = 4. The structure was determined from single crystal X-ray diffraction data and refined to final residual factors R(F) = 0.030 and Rω(F) = 0.035 for 32 variable parameters and a unique data set of 1100 diffraction intensities [I > 3σ(I)]. The U atoms are located on two 4c non equivalent crystallographic positions. U(1) has a 7-fold coordination of Te atoms with a coordination polyhedron deriving from an octahedron in which one apex is split into two positions, and U(2) has a monocapped trigonal prismatic coordination. U 2 Te 3 exhibits rather complex magnetic behaviour, with an onset of ferromagnetic order at T ∼ 110 K and spin reorientation below 105 K.

Uranium cobalt tetraaluminide, UCoAl4.

The structure of UCoAl(4) can be viewed as a succession of atomic layers, with the compositions UCoAl and Al(3), that alternate along the c axis. The packing within the pure Al layer at z = 1/2 results from edge-sharing of triangles, squares and pentagons of Al atoms. Two successive Al(3) layers thus define pentagonal, square-based and trigonal prisms which are centred at z = 0 by the U, Co and remaining Al atoms. UCoAl(4) is a high-temperature phase that is only observed in as-cast samples.

SPIN-GLASS BEHAVIOUR OF NOVEL TERNARY URANIUM ALUMINIDE U3Co4 +xAl12-x (x=0.55)

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 T f = 8–10 K that depends weakly on the applied magnetic field. The observed pronounced difference between the ZFC and FC magnetizations, as well as the decay in the remanent, both give evidence that a highly irreversible, frozen state is formed below T f which is reminiscent of spin-glass behaviour. The real and imaginary parts of the ac susceptibility show that the corresponding T f peaks are 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 T f.

Liquidus Projection of the B-Fe-U Diagram: The Boron-Rich Corner

The liquidus projection at the boron-rich corner of the B-Fe-U phase diagram is proposed based on powder X-ray diffraction measurements, heating curves, and scanning electron microscopy observations, complemented with both energy dispersive X-ray spectroscopy and electron probe microanalysis. Evidence for six ternary reactions is presented, the corresponding 12 monovariant lines are drawn, and the nature and location of the ternary reactions are given. The ternary compounds existing in this region of the B-Fe-U ternary phase diagram, UFeB4 and UFe2B6, were confirmed to be formed by ternary peritectic reactions, yet UFeB4 has a considerably larger primary crystallization field, which points to an easier preparation of single crystals of this compound, when compared with UFe2B6.

Peculiarities of U-based Laves phases

This contribution focuses on the structural and physical properties of U-based Laves phases. It starts with the structural description of the different type of Laves phases, followed by a brief description of the factors that affect their stability. The majority of the uranium Laves phases show a weakly paramagnetic behaviour. The reason is the compact structure of the phases that leads to small a U-U spacing as well as very high coordination numbers, regarding both the uranium and the ligands sublattices, which brings a strong hybridization with non-f states. However, there are some exceptions of uranium Laves phases that do order magnetically (UFe2, UNi2 and the recently discovered U2Fe3Ge compound). These exceptions are discussed in more detail in the present manuscript.

Neutron diffraction study of magnetic ordering of two binary uranium tellurides U3Te5 and U2Te3

Abstract 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.

Crystal structure and properties of the binary uranium telluride U2Te5

Abstract 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.