A new black quaternary oxide Sr5BiNi2O9.6 was synthesized by solid state reaction at 1200°C. Its structure was solved by electron crystallography and X-ray powder refinement, yielding a tetragonal structure with space group I4/mmm, a=5.3637 (2)Å, c=17.5541(5)Å, Z=4. The structure can be described as a stacking of (Bi,Sr)–O rocksalt slabs and SrNiO3−δ perovskite slabs. The initial nickel valence is close to +3.1. Thermogravimetry and high-temperature oxygen coulometry showed that this compound has variable oxygen content as a function of temperature and oxygen pressure, and ultimately decomposes when heated in low oxygen pressure above 800°C. It is a metallic conductor with n-type conduction. Its thermoelectric power was determined and found to be −20 and −38μV/K at 300 and 650°C, respectively. Magnetic measurements confirm the nickel valence close to +3 and show evidence of magnetic ordering at 20K.

Fourier images (the Talbot effect) are a special self-imaging phenomenon arising from the coherent illumination of a periodic object.The formation mechanism has been carefully analyzed by J. M. Cowley and A. F. Moodie with diffraction theory in the 1950s [1].Here we report the experimental observation of Fourier images in coherent convergent beam electron diffraction (CBED) patterns taken using high energy incident electrons.We use a transmission electron

The ab initio structure determination using precession electron diffraction will be discussed for different examples of complex oxides.The focus of the study is on the possibility to determine the oxygen positions in compounds containing heavy scattering elements.The effect of recording techniques, presence of heavy scatterers, cell volume, symmetry, and other aspects will be elaborated upon.The possibility to localize the oxygen atoms will be demonstrated using a relatively simple rutile type SnO 2 structure.The solution obtained with the precession electron diffraction data is in excellent correspondence with the structure refined from X-ray diffraction data.The application of the precession electron diffraction technique to more challenging structures will be shown using the examples of the Sr 3 AlMn 2 O x phase (high unit cell volume, low symmetry) and the PbMnO 2.3 phase (large unit cell volume, presence of very heavy scatterer such as Pb).For such compounds precession electron diffraction is a promising tool for obtaining structural information because conventional structure solution using powder diffraction data is hampered by the multiphasic nature of the samples and the weakness of the superlattice reflections originating from the ordering of oxygen atoms and vacancies.

Oxides synthesized in high temperature / high pressure conditions often show complex structures and contain several phases which makes a structure solution by X-ray crystallography very difficult or even impossible. Electron crystallography can then be a powerful alternative. We show here the structure solution of 3 oxides by precession electron diffraction. The phases include a simple hexagonal structure (AgCoO2), a complex monoclinic structure (PbMnO2.75) with a quasi 2-dimensional unit cell and a complex trigonal structure (LiTi1.5Ni0.5O4). In the last case even the positions for the light element Li were determined.

A sample having stoichiometry Li[Ti(1.5)Ni(0.5)]O(4) has been synthesized to obtain a spinel structure. The resulting crystalline powder revealed a multiphase nature with spinel as the minor phase. The main phase is a new trigonal phase having a = 5.05910 (1), c = 32.5371 (1) A. The structure has been solved by direct methods working on a three-dimensional set of intensities obtained from a precession electron-diffraction experiment, and refined on synchrotron powder diffraction data in the space group P3c1. The model consists of hexagonal layers of edge-sharing octahedra occupied either by the heavy cations Ti and Ni, or preferentially by Li. On the basis of cation-site occupancies the stoichiometry becomes Li(4)Ti(8)Ni(3)O(21), which is compatible with the microanalysis results.

High resolution powder diffraction was used to characterize a sample of Ag(pyz)2S2O8.Measurements were taken at beamline X16c at the National Synchrotron Light Source at Brookhaven National Laboratory.The sample was found to contain multiple phases.Subsequent measurements, several months later, showed that a number of diffraction peaks had decreased dramatically in intensity.This is indicative that one phase had partially transformed, presumably into another, already present, phase.The disappearing peaks were indexed as c-centered monoclinic, with lattice parameters a = 15.969Å b = 7.133 Å c = 14.586Å β = 124.971°,and a candidate structure found.Due to the presence of multiple phases in the sample, however, ordinary Rietveld refinement of this structure was impossible.A robust refinement 1 procedure was implemented to refine the structure of the disappearing phase in the presence of other, unknown, phases.This was done using the software TOPAS Academic by continuous readjustment of the weights used in the figure of merit calculations, effectively changing χ 2 into its robust equivalent.The refined structure contains 4-coordinated silver, bonded in a square planar configuration to the nitrogen atoms of the pyrazine rings.The peroxodisulfate ions are located between the sheets of Ag(pyz)2.The robustly refined structure will be presented, and compared to previous knowledge of this material.