J.C. Spirlet

A new family of actinide ternary intermetallic compounds

Abstract We have prepared an extended group of compounds of the general formula An 2 T 2 X (AnU, Np; T Ni, Co, Rh, Pd, Pt, Ir; XIn, Sn), which crystallize in the tetragonal structure (U 3 Si 2 type). The lattice parameters and atomic positions were determined using X-ray diffraction on single crystals. Preliminary magnetic and Mossbauer spectroscopy data show that we can follow the onset of magnetism within this group, which can be correlated with the Hill criterion and the development of 5f-d hybridization.

The preparation and purification of americium metal by evaporation

Abstract In order to redetermine some physical and chemical properties of americium metal, several grams of 241 Am have been prepared by two independent methods: lanthanum reduction of the oxide and thermal dissociation of the intermetallic compound Pt 5 Am. After its separation from excess lanthanum or alloy constituent by evaporation, americium metal was further purified by sublimation at 1100 C and 10 −6 Torr. Irrespective of the method of preparation, the temperatures of evaporation or condensation and the material of the condenser, the americium samples displayed the same d.h.c.p. crystal structure. As determined by vacuum hot extraction, the oxygen, nitrogen and hydrogen contents are equal or smaller than 250, 50 and 20 ppm, respectively.

Heavy fermion behavior of U2T2X compounds

Magnetic and specific-heat studies of U[sub 2][ital T][sub 2][ital X] compounds show a frequent occurrence of the [gamma] enhancement in conjunction with the onset of antiferromagnetic ordering. The largest value of 830 mJ/mol K[sup 2] was observed in U[sub 2]Pt[sub 2]In, which is nonmagnetic down to 1.2 K. Variations of electronic structure are documented by optimized relativistic LCAO calculation.Magnetic and specific‐heat studies of U2T2X compounds show a frequent occurrence of the γ enhancement in conjunction with the onset of antiferromagnetic ordering. The largest value of 830 mJ/mol K2 was observed in U2Pt2In, which is nonmagnetic down to 1.2 K. Variations of electronic structure are documented by optimized relativistic LCAO calculation.

Phase transformation of AnX compounds under high pressure (An ≡ Np, Pu; X ≡ Sb, Te)

Abstract High pressure X-ray diffraction studies were performed on AnX compounds (An ≡ Np, Pu; X ≡ Sb, Te) in the pressure range up to about 57 GPa, at room temperature, using a diamond anvil cell in an energy-dispersive X-ray diffraction facility. These AnX compounds have an f.c.c., NaCl-type structure at ambient pressure and undergo first-order phase transitions under pressure. Whereas NpTe and PuTe transform to a primitive cubic cell of the CsCl type at 13 GPa and 15 GPa respectively, a tetragonal structure, space group P 4/ mmm , is observed for NpSb above 10 GPa. This tetragonal structure can be regarded as a “distorted” CsCl-type structure, the atomic positions being the same as in the cubic CsCl cell. In PuSb two transitions are detected: the CsCl-type structure is observed above 17 GPa; then PuSb transforms to the tetragonal P 4/ mmm structure at about 42 GPa. In addition, the compressibility of the low pressure phase was determined from the V ( p ) data for each compound.

Neutron diffraction on actinides

The evperimental methods of elastic neutron scattering are briefly reviewed and their impact on the physics of the actinides is illustrated by typical evamples such as investigations of magnetic ordering in actinide monopnictides (incommensurate and multi-K structures), study of vuadrupolar ordering in UO2, form factor determination in USb and PuSb and study of anisotropic interactions by measuring the critical scattering in UAs.

X-ray diffraction study of protactinium metal to 53 GPa

Abstract High purity protactinium was studied by X-ray diffraction in a diamond anvil cell up to 53 GPa. The body-centred tetragonal structure was retained through the whole pressure range. A bulk modulus B 0 = 157(5) GPa and a pressure derivative B ′ 0 = 1.5(0.5) were deduced from a Birch fit of the combined data of two independent series of measurements. While the bulk moduli determined by the same method for the neighbouring elements Th and U are in relatively good agreement with those calculated by the LMTO method, the experimental bulk modulus for protactinium is higher than the calculated one by about 40%. The high bulk modulus suggests high 5f participation in the bonding of protactinium metal.

Neutron diffraction studies of the crystalline and magnetic properties of UFe2

Studies using both polarised and unpolarised neutrons have been performed on single crystals of the Laves phase intermetallic compound UFe2. The authors describe studies of the twinning characteristics (two crystals with a common (1, 1, 1) axis) of the sample, a feature that is probably common in these cubic compounds. They then describe studies with polarised neutrons to determine the magnitude of the spin and orbital moments on the uranium site. In agreement with a recent theoretical prediction these two moments are found to be almost equal, but oppositely directed in real space. The net moment at the U site is only 0.01 mu B. The polarised neutron experiments also allow them to put an upper limit on any possible anisotropy in the magnetisation. High-field magnetisation experiments up to (20 T) on the same crystal as used in the neutron experiments allow them to determine the conduction-electron polarisation.

High pressure x-ray diffraction studies on ThS up to 40 GPa using synchrotron radiation

Abstract High pressure X-ray diffraction studies (up to 40 GPa) were performed on ThS using synchrotron radiation and a diamond anvil cell. The measured value of 145 GPa for the bulk modulus B0 disagrees with a previous measurement. The high pressure behaviour indicates a phase transformation to ThS II starting at 15–20 GPa. The transformation is of the second-order type, and the resulting structure can be described as distorted f.c.c.

High pressure x-ray diffraction experiments on US using synchrotron radiation

Abstract High pressure X-ray diffraction studies (up to 40 GPa) were performed on US using synchrotron radiation and a diamond anvil cell. The measured value of 92 GPa for the bulk modulus B0 is in reasonable agreement with calculations. The high pressure behaviour indicates a phase transformation to US III at about 15 GPa. The transformation is a smooth deformation process, which starts with a tetragonal structure ( a tetr = a cub 2 1 2 ; ctetr = 2acub) and continues with an orthorhombic structure (a = 375(3) pm; b = 345(3) pm; c = 1069(24) pm) at 35 GPa; it is second order within experimental error and it should involve some contributions from uranium f electrons.

Structural stability and equation of state of thorium carbide for pressures up to 36 GPa

High-pressure X-ray diffraction studies have been performed on ThC powder up to 36 GPa. No structural phase transformation has been observed, the rock-salt structure of ThC being stable over the whole pressure range. The equation of state can be described by the Murnaghan equation with the bulk modulus B0 = 109(7) GPa and its pressure derivative B′0 = 3.1(6). The high-pressure behaviour of ThC is compared with that of other actinide carbides and nitrides and correlated with the occupation of the 5f electron shell.