Th. Zeiske

Crystal structure of brucite-type cobalt hydroxide β-Co{O(H,D)}2 — neutron diffraction, IR and Raman spectroscopy

Abstract The crystal structure of brucite-type Co(OD)2 (space group P3ml, Z = 1, a = 317.79(4) pm and c = 464.2(1) pm, RI = 5.89%) has been refined by neutron powder diffraction studies on the basis of 671 observations and 44 reflections. Infrared and Raman spectra of cobalt hydroxide at different degrees of deuteration are presented and assigned to the internal, librational and translational modes. The D⋯O distance of 252.8 pm and the wavenumbers of the OH and OD stretching modes (3604 and 2665 cm−1, 90 K, mean values of the unit-cell group modes) do not exclude the formation of weak trifurcated hydrogen bonds. The librational and translational vibrations of Eu species are strongly coupled as shown by the respective isotopic shifts. A reassignment of the IR-allowed librations and lattice vibrations of transition metal brucite-type hydroxides is given.

X-ray superstructure determination of ordered oxygen and Cu-displacements in a single domain of YBa2Cu3O6.35

AbstractThe superstructure of ordered oxygen atoms in a single domain of YBa2Cu3O6.35 has been determined by X-ray diffraction. The 45o rotated superstructure cell is orthorhombic—spacegroup Pbam, lattice constants

Antiferromagnetic fluctuations in a modified pyrochlore

2\sqrt 2 a \times \sqrt 2 a \times c

A REINVESTIGATION OF THE FIELD-INDUCED MAGNETIC FORM FACTOR OF CHROMIUM

, witha=3.8652(3) Å,c=11.815(2)Å the dimensions of the fundamental tetragonal cell. The arrangement of the oxygen atoms in the basal plane minimizes their electrostatic repulsion by avoiding near and next-near neighbors. There are displacements of copper atoms of 0.13 Å in the Cu(1) plane and 0.06 Å in the Cu(2) plane. Only 12% of the oxygen atoms in the basal plane contribute to the superstructure.

TWO-DIMENSIONAL MEASUREMENTS OF THE COMMENSURATE DIFFUSE SCATTERING IN CHROMIUM

Abstract In a single crystal of YBa 2 Cu 3 O 6.35 we determined an oxygen superstructure with a 2√2 a X2√2 a cell by neutron diffraction. A 2√2 a X√2 a superstructure of a monodomain has been found by X-ray diffraction. In YBa 2 Cu 3 O 6.4 of T c =38K, we observed a short range ordered ortho-II structure by neutron single crystal diffraction.

Two-dimensional measurements of magnons

Abstract Comparing elastic with quasielastic neutron diffraction data we observe a spin freezing in the modified pyrochlore CsNiCrF 6 around its spin glass temperature ( T G = 2.3 K). However, even below T G there is still significant inelastic intensity in the magnetic diffuse scattering extending to at least 4 meV ⪢ kT G .

The partial conversion of incoherent into coherent neutron scattering from rotating molecules

The structure of (Bi/Pb)2Sr2FeO6.25 was refined from high resolution neutron powder diffraction data taken at 300 K and 5 K. The average structure is well described in the orthorhombic spacegroup Amaa witha=5.4254 Å,b=5.4909 Å andc=23.2245 Å. The FeO6 octahedra are tilted by 2.7° towards (0 1 0). The oxygen positions in the (Bi/Pb)O-layers are consistent with the occurrence of (Bi/Pb)−O−(Bi/Pb) chains. Excess oxygen was located between these chains. Antiferromagnetic 3-dim ordering of the Fe-moments withM=(2, 1, 2) μB was observed at 5 K with the wavevector pointing along (1 0 0).

Canted antiferromagnetism and magnetoelastic coupling in metallic Ho 0.1 Ca 0.9 MnO 3

Abstract Results of a neutron diffraction study of the field-induced magnetic form factor of pure antiferromagnetic chromium are presented. The data is analysed by means of a classical Fourier technique as well as a maximum entropy analysis. In agreement with earlier measurements, we can describe our data by a 60% orbital and 40% spin contribution. Both Fourier and maximum entropy analysis indicate a slight anisotropy of the magnetisation density. However, in an attempt to model the induced moment form factor using symmetry adapted functions for the d-orbitals only, we could not reproduce a significant difference in the occupation of eg and t2g states.