J. Le Roy

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.

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  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  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.

Magnetic structures of Nd2Fe2Si2C and Tb2Fe2Si2C

Abstract Magnetic properties of R2Fe2Si2C (with R = Nd, Tb) have been studied by means of neutron diffraction. An antiferromagnetic behaviour have been evidenced below 15 K for the Nd based compound and 45 K for the Tb based compound. The magnetic cell is twice the crystallographic one, with a propagation vector k = (0, 0, 1 2 ) . The main original feature of both structures is the non-colinearity between both R and Fe sublattices, the magnetic moments being nearly perpendicular.

A new phase in the TlAgTe system: crystal structure of Tl4Ag24−xTe15−y

Abstract A new stable phase Tl 4 Ag 24− x Te 15− y in the ternary TlAgTe system has been identified by X-ray diffraction on single crystals. The space group is P 6 and the lattice parameters are a = 1.1418(4) nm and c = 0.9220(1) nm with one formula per unit cell ( Z = 1). The structure is described as an arrangement of two types of channels parallel to the [001] direction. Two-thirds of these channels are hexagonal and built up with silver and tellurium atoms, hosting thallium atoms. One-third are octahedral chains of silver atoms with centres statistically occupied by tellurium atoms. In addition, the refinement indicates partial occupation of some silver positions.

Structure of lithium iodate - iodic acid solid solution Li1-xHxIO3 (x = 0.33)

Abstract The structure of the solud solution Li 1-x H x IO 3 ( x = 0.33) is determined at room temperature by X-ray single crystal and neutron powder diffraction. The space group is found to be P6 3 like α-LiIO 3 . Hydrogen atoms are in general positions with the occupation factor 0.33 and form weak bonds with neighbouring oxygens. The structure is briefly compared with that of α-LiIO 3 .

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.

A Search for New Permanent Magnet Materials: Crystallographic and Magnetic Properties of New Compounds

Permanent magnet materials are characterized by high Curie temperature, large spontaneous magnetization and large magnetic anisotropy. The best natural elements to produce these properties are rare earth and transition elements (Fe and Co). New materials could be obtained by addition of others elements such as B, Si or C which stabilized the corresponding atomic structures. New compounds have been synthetized and their crystallographic and magnetic properties have been studied : Nd(CoxMn1-8)12, Nd(N1xMn1-x)12, RFe10SiC0.5 (R = Ce, Pr, Nd, Sm), DyFe2SiC, DyFe2Si2C, R(FexCo1-x)10SiC0.5. Curie temperatures of 950 K for NdCo10SiC0.5 and 670 K for SmCo10SiC0.5 were measured.