B. Lambert-Andron

Metallurgical and physical study of praseodymium disilicides and digermanides

Abstract The series of disilicides and digermanides of praseodyme with the composition PrX 2− x (XSi or Ge) were investigated using X-ray diffraction, metallographic studies, electrical resistivity and magnetic measurements. The original result presented here is evidence of new phases that can be identified as ordered and disordered variants of the ThSi 2 structure in digermanides. These phases have the same basic orthorhombic GdSi 2 -type structure as in disilicides. Consequently, the phase diagram in the RX 2− x region is presented and discussed with some focus on the physical behaviour in relation to the two-phase equilibrium.

Structural investigations by neutron diffraction of equi-atomic Zr–Ti(V)–Ni(Co) compounds and their related hydrides

Abstract Crystal structure refinements based on neutron diffraction experiments performed on the ternary compounds ZrTiNi, ZrVCo and ZrVNi allow to confirm the stability of the C14 Laves type of structure in a large extent of formula. Besides, SEM/EDX analyses reveal the presence of minor additional phases that precipitate parallel to the main one. Neutron diffraction experiments performed on the corresponding ZrMM′ hydrides indicate that after hydrogen (deuterium) absorption the crystal structure remained unchanged, except for ZrTiNi, where further investigations are underway.

CRYSTAL STRUCTURE AND PROPERTIES OF TETRAGONAL CEGE1.6

Abstract An X-ray study was performed on single crystals of the compound CeGe 1.6 . The structure is derived from the tetragonal α-ThSi 2 type. The superstructure is shown to be related to the order of vacancies. Magnetic measurements and neutron diffraction experiments showed a ferromagnetic structure with magnetization along the c axis, T C = 6 K and M = 1.5 μ B at T = 1.5 K. The crystal field level scheme is deduced from single-crystal susceptibility and inelastic neutron scattering.

Coexistence of ordered and disordered phases in a CeGe2−x single crystal

Abstract The phase diagram of the CeGe 2− x compounds (0.1 1.54 is observed by optical microscopy. The two phases are identified by X-ray diffraction as ordered and disordered variants of the ThSi 2 structure; their magnetic properties are characterized by neutron diffraction, magnetic and resistivity measurements.

Structural chemistry of a new ternary zirconium cobalt phosphide, Zr5Co19P12

Abstract Zr5Co19P12 has a new structural type closely related to Hf2Co4P3. It has hexagonal symmetry with the space group P 6 2m (D3h3) and the lattice constants a = 11.885(6) A , c = 3.596(3) A , c a = 3.304(9) , v = 439.32 A , with one formula unit per cell. This structure is connected to those of binary and ternary transition metal phosphides and can usefully be described in the same way on the basis of the phosphorus lattice.

Preparation, crystal structure and magnetic properties of Dy5Ru19P12 and isotypic lanthanoid ruthenium phosphides

Abstract The new phosphide compounds Ln5Ru19P12 (Ln ≡ Y, La, Ce, Pr, Nd, Sm, Gd,Tb, Dy, Ho, ErandYb) were prepared by reacting the elemental components and annealing at 1700 K. The crystal structure of Dy5Ru19P12 was determined from single-crystal X-ray data and refined to a residual of 0.044 for 562 unique structure factors with 23 variable parameters. Dy5Ru19P12 crystallizes with a hexagonal structure type derived from Hf2Co4P3 with one formula unit per cell and the lattice constants a = 12.465 A , c = 3.940 A . The Ln5Ru19P12 compounds are isotypic with Dy5Ru19P12, and their lattice constants are reported. Their magnetic properties have been studied. The compounds with a magnetic rare earth show a spontaneous magnetization at low temperature and then follow a paramagnetic Curie-Weiss law.

X-ray and magnetic single-crystal analysis of the crystallographic structure of the Y3(Fe0.933V0.067)29 compound

Abstract The formation of a sizeable single crystal of the Nd 3 (Fe,Ti) 29 -type phase, namely Y 3 (Fe 0.933 V 0.067 ) 29 is reported. It was prepared by the solid-state transformation of a Y 2 (Fe,V) 17 single crystal whose chemical composition is Y 3 (Fe,V) 29 . Initial disagreement between powder and single-crystal X-ray data has been resolved by performing magnetization measurements on single crystal. These measurements show a peculiar behaviour and have been quantitatively analysed by considering that the crystal is actually twinned. Refinement of the single-crystal data is then re-examined and confirms the monoclinic structure already reported for this system.

Phase separation and magnetic structure in praseodymium disilicide

Praseodymium disilicide exhibits a phase separation near 200 K into two nearly tetragonal phases. The lattice parameters and the proportion of each phase are studied as functions of the temperature by X-ray and neutron diffraction; anomalous thermal expansion is observed for one of them. Both phases order magnetically at 12 K, with different magnetic structures.

Structural chemistry of a new ternary uranium rhodium phosphide - U6 Rh20 P13

The new compound U6Rh20P13 has been prepared, starting from the elemental components. Its crystal structure, determined from single crystal X-ray data is isotypic with Zr6Ni20P13, hexagonal symmetry, space group P6 - C3h with one formula unit per cell and the lattice constants a = 13.259(7) A, c = 3.896(7) A, c/a = 3.40, V = 685 A3. The structure is closely related to those of binary M2P and ternary rare earth-transition metal phosphides (□,Ln,M)2P and can be usefully described in the same way on the basis of the phosphorus lattice. U6Rh20P13 is the first compound presenting an uranium insertion in a triangular prismatic site of phosphorus, opening the way to the finding of numerous new uranium-transition metal pnictides.

The coexistence of two phases with ordered and disordered vacancies in PrGe1.6

The PrGe1.6 compound shows two coexistent crystallographic structures, which are ordered and disordered variants of the ThSi2 structure, the ordered phase resulting from the ordering of Ge vacancies. Comparison is made with CeGe1.6 and Ce and Pr silicides, which exhibit the same type of phase separation.