D.J.W. IJdo

Preparation, crystal structure, and magnetic structure of LiCrS2 and LiVS2

Abstract The crystal structures of LiCrS 2 and LiVS 2 are described. The anion-cation arrangement is like that in NiAs with ordering of Li and Cr (V) in alternating layers. The magnetic structure of LiCrS 2 which shows a spin ordering at 4.2°K was determined by means of neutron powder diffraction. The spin structure consists of a triangular arrangement within the hexagonal planes with antiparallel coupling between adjacent planes, i.e., an ordering of the third kind. In LiVS 2 no ordering was observed at 4.2°K.

Magnetic and crystallographic structures of MexNbS2 and MexTaS2

Abstract The crystal structures of the compounds MexNbS2 and MexTaS2 with x = 1 3 and 1 4 are described. The magnetic structures of those compounds which show magnetic ordering at 4.2°K were also determined by means of neutron powder diffraction. The compounds with x = 1 4 show an anomaly in the χ−1 versus T curve. This phenomenon is shown to be correlated with a discontinuity in the variation of the c a ratio with temperature.

The orthorhombic fluorite related compounds Ln3IrO7

Abstract Fluorite-related Ir(V) compounds with the composition Ln 3 IrO 7 have been prepared. The structure of these phases is orthorhombic with space group Cmcm. It is a superstructure of the cubic fluorite structure with unit cell parameters a orth ≈ 2a c , b orth ≈ C orth ≈ a c √2, as in La 3 NbO 7 . The structure determination has been performed using Rietveld refinement on X-ray powder diffraction data.

The orthorhombic gluorite related compounds Ln3RuO7, LnNd, Sm and Eu

Fluorite-related (Ru(V) compounds with composition Ln3RuO7 have been found. These compounds with space group Cmcm adopt a superstructure of the cubic fluorite structure with aorth=2ac, borth=ac✓2. These compounds have the same structure as La3NbO7.

Structures and magnetic properties of Ln3OsO7 (Ln=Pr,Nd,Sm)

Abstract Polycrystalline samples of Ln3OsO7 (Ln=Pr,Nd,Sm) have been prepared. The structures of these compounds were determined by X-ray powder diffraction. They crystallize in a superstructure of cubic fluorite (space group Cmcm, Z=4). The samples have been characterized by magnetometry. The compounds show complex magnetic behavior at low temperatures caused by competing magnetic interactions leading to frustration.

Oxygen evolution and reduction on iridium oxide compounds

Abstract The electrochemical properties of twelve iridium oxide compounds (including pyrochlores, perovskites, fluorites and compounds of another structure) were examined with respect to the oxygen-evolution and the oxygen-reduction reactions. Steady-state current-potential curves were measured in 45% KOII. In addition, the kinetic properties and the electrical conductivity of four iridium oxide pyrochlores were investigated. All twelve compounds have a moderate to high catalytic activity for the oxygen-evolution reaction, and a somewhat lower activity for the oxygen-reduction reaction. Pb 2 (Pb x Ir 2– x )O 7– y and Nd 3 IrO 7 showed the highest activity towards both reactions.

Yellow zirconate luminescence in Ca3ZrSi2O9

Abstract The compound Ca 3 ZrSi 2 O 9 which contains edge-sharing pairs of zirconate octahedra shows a luminescence emission with an unusually long wavelength (maximum 540 nm).

Interrelation of Structure, Dimensionality and Superconductivity in the High-Temperature Superconductor YBa2Cu3O7-δ

We have measured x-ray diffraction (XRD), high-resolution electron microscopy (HREM), resistivity and susceptibility for a series of differently prepared YBa2Cu3O7-δ samples. The high-temperature superconductivity was studied as a function of variable quench temperature. Quenching above 820 °C leaves the sample in the tetragonal phase and destroys the superconductivity. We suggest that the supercondutivity is located in the CuO chains which are extremely sensitive to oxygen loss.

The ordered perovskite system Ln2NiRuO2

Abstract A new series of perovskite phases, Ln 2 NiRuO 6 with Ln = La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er and Tm, has been prepared. The structure of La 2 NiRuO 6 has been refined by Rietveld analysis of neutron powder diffraction data.La 2 NiRuO 6 : M = 533.60, monoclinic, P2 1 /n. At T = 293 K: a = 5.5688(4) A , b = 5.5984(4) A , c = 7.8764(6) A , β = 90.18(1)°, V = 245.56(1) A 3 , Z = 2 . [ D x = 7.22(1) Mg/m −3 , μ R = 0.22, λ = 2.5830(5) A , R wp = 6.80% ] for 116 reflections. The structure is monoclinic GdFeO 3 type perovskite with complete ordering between Ni and Ru. X-ray diffraction patterns of all members of this series indicate the same structure.

The crystal structure of Ni5TiB2O10

Abstract The crystal structure of Ni 5 TiB 2 O 10 was determined by single crystal X-ray analysis. The compound has the same structure as the mineral ludwigite. The orthorhombic celldimensions and space group are a =9.206(7) A , b =12.224(9) A , c =2.994(2) A , Pbam z=2. Ti and Ni are disordered on one equipoint.