J.M. Moreau

A new phase in Nd2Fe14B magnets. Crystal structure and magnetic properties of Nd6Fe13Si

Abstract A new stable phase has been identified in the Nd-Fe-Si system. X-ray diffraction examination of single crystals was used to establish the crystal structure of Nd 6 Fe 13 Si. The tetragonal space group is I 4/ mcm and the lattice parameters are a = b = 0.8034(3)nm, c = 2.278(1)nm. The crystal structure is an ordered version of Nd 6 Ga 3 Fe 11 .Magnetic measurements show an antiferromagnetic behaviour.

A new phase in the NdFe system: Crystal structure of Nd5Fe17

Abstract A new stable phase in the Ndue5f8Fe system has been identified. X-ray diffraction examination of single crystals was used to establish the crystal structure of Nd5Fe17. The hexagonal space group is P6 3 mcm and the lattice parameters are a = 2.0214(8) nm, c = 1.2329(8) nm, Z = 12. The Nd5Fe17 structure is built up of layers which are a tessellation of triangles, pentagons, hexagons and heptagons. The stacking of layers forms antiprisms. Clusters of neodymium atoms only are made of trigonal antiprisms or regular octahedra stacked upon each other to form infinite columns. Each neodymium cluster is surrounded by a first ring of nine pentagonal antiprisms centred by iron atoms and a second ring of 12 antiprisms with hexagonal and heptagonal faces centred by neodymium atoms.

Crystallographic and magnetic properties of a new series RFe10SiC0.5 (R ≡ Ce, Pr, Nd, Sm)

Abstract X-ray diffraction studies on single crystals were used to establish the crystal structure of the new compound NdFe10SiC0.5, which has space group I41/amd, with Z = 4 formula units per cells. The lattice constants are a = 10.037(7) A and c = 6.495(4) A . The final value of R was 0.05 for 283 independent intensities. The positions of the neodymium, iron and silicon atoms correspond to the BaCd11 structure. The carbon atoms fill octahedral vacancies formed by four iron and two neodymium atoms, with an occupancy of 25%. The series RFe10SiC0.5 (R ≡ Ce, Pr, Nd, Sm) are isotypic with NdFe10SiC0.5 and all these compounds are isotypic with LaMn11C2−x. Magnetic measurements were made on all the series and showed ferromagnetic behaviour with a mean iron moment of about 1.4 μB at low temperatures. The Curie temperatures lie between 390 K and 460 K.

Refinement of the crystal structure of R1 + ϵFe4B4 compounds (R ≡ Nd, Gd)

Abstract The crystal structures of the R1 + ϵFe4B4 compounds were recently described as resulting from essentially two independent substructures. In addition, a periodic modulation of the Fe tetrahedra, induced by interactions with the R sublattice, was shown to occur. The accurate refinements of the structure of gadolinium and neodymium compounds are described in this paper. It is shown in particular that the modulation of the Fe tetrahedra allows essentially an increase of the shortest R-Fe interatomic distances.

RM3Ga2 Compounds (R ≡ rare earth, M ≡ Co, Ni): A new structural series

Abstract X-ray diffraction on single crystals was used to establish the crystal structure of YCo 3 Ga 2 and YNi 3 Ga 2 . This hexagonal structure belongs to the P 6/ mmm space group. RCo 3 Ga 2 compounds with R ≡ La — Er and RNi 3 Ga 2 with R ≡ La — Tm crystallize with the same structure which is closely related to the hexagonal CaCu 5 -type structure.

New phases in the system LaCu

Abstract The phase diagram of the Laue5f8Cu system was reinvestigated by DTA in the concentration range 0–33 at.% La. The crystal structures of the various intermetallic compounds were examined by X-ray diffraction on powdered or single-crystal specimens. Two new phases, X (7.5 at.% La) and LaCu4, were observed besides the well-known compounds LaCu6, LaCu5 and LaCu2. X forms by peritectic reaction (873 °C) and decomposes on cooling. LaCu4 forms by peritectic reaction (743 °C). Its crystal structure is tetragonal (space group I 4 m2 ) with a = 0.8904 nm, c = 1.9210 nm and Z = 18.

Rare earth-iridium compounds with Pu5Rh3 and Y3Rh2 structure types: Members of a new structural series with formula R5n + 6T3n + 5

Abstract The structures of the rare earth-iridium compounds R 5 Ir 3 and R 3 Ir 2 were identified from X-ray powder diagrams. R 5 Ir 3 compounds (R ue5fb La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, Y) crystallize with the tetragonal Pu 5 Rh 3 structure type. R 3 Ir 2 compounds (R ue5fb Gd, Tb, Dy, Ho, Er, Y) crystallize with the tetragonal Y 3 Rh 2 structure type. The Pu 5 Rh 3 type is a structure block shift variation of the W 5 Si 3 type. The W 5 Si 3 , Pu 31 Pt 20 and Y 3 Rh 2 structures are members of a structural series with the formula R 5 n + 6 T 3 n + 5 in which n takes the values ∞, 5 and 3 respectively.

Y3RhSi3: Member of the structural series with formula Rn + 2T2Sin + 2

X-ray diffraction examination of single crystals was used to establish the crystal structure of Y3RhSi3. The structure, which is isotypic with Sc3NiSi3 (monoclinic space group C2/m), consists of bands of four infinite columns of trigonal prisms connected by two infinite columns of yttrium or rhodium trigonal prisms. All these prisms are silicon centred. This compound belongs to a new series with the general formula Rn + 2T2Sn + 2 where n represents the number of trigonal prisms in each band.

Structure of ordered Gd2Co7-type Y4Rh9Si5

Single-crystal X-ray diffraction was used to establish the crystal structure of Y4Rh9Si5, (space group, R3m) with lattice parameters a = 5.496 A and c = 33.176 A. The structure is an ordered version of the Gd2Co7 type with rhodium and silicon occupying the corresponding cobalt sites. It consists of stacks of blocks corresponding to the CaCu5-type structure and the MgCu2-type structure.

R5T3 compounds (R ≡ rare earth; T ≡ Rh, Ir) with an Mn5Si3-type structure

Abstract X-ray diffraction on a single crystal was used to establish the crystal structure of Ho5Rh3. A hexagonal structure of the Mn5Si3 type with space group P63/mcm and lattice constants a = 8.100 A and c = 6.337 A was determined. Gd5Rh3, Tb5Rh3, Dy5Rh3, Er5Rh3, Tm5Rh3 and Lu5Rh3 are isostructural with Ho5Rh3. X-ray powder diagrams taken with a Guinier camera on the high temperature phase of R5Ir3 compounds (R ≡ Tb, Dy, Ho, Er, Tm, Lu) were indexed using Mn5Si3 structure parameters. A single-crystal study of Lu5Ir3 and Er5Ir3 showed weak superstructure reflections.