J. Allemand

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.

Structural characterization and superconducting properties of (Tl0.5Pb0.5)(Sr2−xBax)Ca2Cu3O9−δ

Abstract Samples of nominal composition (Tl0.5Pb0.5)(Sr2−xBax)Ca2Cu3O9−δ, 0 ≤ x ≤ 0.6, and (Tl0.6Pb0.2Bi0.2)(Sr1.8Ba0.2)-Ca2Cu3O9−δ were characterized by X-ray powder diffraction, scanning electron microscopy and AC susceptibility measurements. In the Bi-free samples, the highest weight fraction of the 1223 phase, 91.3%, was observed for x = 0.4. Above this Ba content, BaPbO3 perovskite appeared as main impurity phase. In the Bi-containing sample the weight fraction was even higher, 92.6%. The Ba content of the 1223 phase, as determined from X-ray diffraction data, was in agreement with the nominal composition of the samples. The unit cell parameters increased when the Sr atoms were progressively replaced by the larger Ba atoms. The refinement of the crystal structure of the 1223 phase revealed a significant off-centering of the Tl site. The distance from the splitted site to the ideal position on the four-fold axis was found to be ∼ 0.26 A for the Ba-containing samples, but only 0.07 A for the Ba-free sample. The distance from the Cu atom to the apical atom of the square pyramid formed by the oxygen atoms increased from 2.29 to 2.50 A as the Ba content was raised. The critical temperature remained between 116 and 120.5 K and was not significantly affected by changes in composition or structure.

RFexSi2 (R ≡ Tb, Dy, Ho, Er, Lu) structures with the non-stoichiometric TbFeSi2 type

X-ray diffraction studies on single crystals of HoFe0.5Si2 were used to establish the crystal structure, with space group Cmcm and lattice constants a = 4.0138(8) A, b = 15.7095(37) A, c = 3.8963(9) A. It is a non-stoichiometric TbFeSi2-type phase with defects, the transition metal site is half occupied by iron and the other sites are fully occupied. We observe the same structure with defects on single-crystal DyFe0.5Si2 and TbFe0.52Si2.

A new phase in the TlAgTe system: crystal structure of Tl4Ag18Te11

Abstract A new stable phase in the ternary TlAgTe system has been identified. X-ray diffraction examination of single crystals was used to establish the crystal structure of Tl4Ag18Te11. The cubic space group is F 4 3m and the lattice parameter is a = 1.8717(8) nm, Z = 8. The relationship to the cubic BaHg11-type structure and the In2Te3-type structure are established. The structure is described as a three-dimensional array of large channels of silver and tellurium atoms hosting linear chains of thallium atoms. These independent channels are built up with cubes and square antiprisms stacked along the fourfold axis and they are connected by smaller channels built up with smaller square antiprisms and cubes hosting tellurium atoms.

Magnetic interactions competing in CeNi1-xCux compounds☆

Abstract We present the crystallographic, electrical and magnetic properties of CeNi 1- x Cu x . An evolution from an enhanced Pauli paramagnetism in CeNi to a Kondo ferromagnet for the intermediate compositions and an antiferromagnetic state for the highest Cu concentrations is found. This behavior is discussed conssidering the changes in volume and density of states which modifies RKKY and Kondo interactions.

A new uranium based compound with a cubic structure UNi0.8Pt0.2

Abstract The crystalline structure of a new Uranium compound with nominal composition UNi0.8Pt0.2 is presented. It has been determined by X Ray Single Crystal and High Resolution Powder Neutron Diffractometries. A cubic, Fd 3 m space group structure, with a cell parameter of a = 6.32773(2) A , was found. The uranium atoms lie in an 8a site, while the Ni/Pt ones are randomly distributed in an 8b site. The U-U distances (2.74 A) are smaller than the the Hill limit and the compound does not present magnetic order.