Strukturaufklaerung neu synthetisierter ionischer Oxide und Keramiken Schlussbericht

The determination of the structure of novel compounds is a precondition for the success of long time preparative projects in solid state chemistry. Some of our scientific projects are hindered by the absence of single crystals for which a structural characterization can be easily done. Because of the application of new powder techniques i.e. X-ray diffraction at a synchrotron or neutron scattering and following combinated structural refinements some difficult problems could be resolved. Examples are the determination of positions and fractions of light atoms besides heavy atoms, the discernment of atoms similar to X-ray diffraction or the determination of new high pressure or high temperature phases. Besides, the structural investigations have been expanded to amorphous systems. Diffraction using high energy photons and application of isotopic contrast technique made it possible to gain detailed information on the short and middle range order of new ceramics. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(78,49) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman

Structural studies of the amorphous silicon boron nitride Si₃B₃N₇

The structure of the new ternary amorphous nitride Si3B3N7, synthesised from the single source precursor TADB [(trichlorosilyl)aminodichloroborane], has been investigated by means of X-ray diffraction using high energy synchrotron radiation and by neutron diffraction using the isotopic contrast technique on nitrogen. The X-ray results have been compared with results from electron diffraction experiments, confirming the trigonal planar coordination of boron (RBN = 1.4 Å, ZBN = 2.8, ZNB = 1.2) by nitrogen and the tetrahedral coordination of silicon (RSiN = 1.7 Å, ZSiN = 3.8, ZNSi = 1.6) by nitrogen. The neutron contrast technique was applied in order to obtain detailed information about the nitrogen environment. From the total pair correlation functions the N–N distances within the boron and silicon coordination polyhedra could be extracted [RNN(B) = 2.5 Å, RNN(Si) = 2.8 Å]. In addition, the difference function shows two distinct maxima at ca. 3.8 and 4.3 Å in the third coordination sphere resulting from Si–N or B–N pairs connected via three bonds. If at least two of these are B–N bonds a contribution to the first peak results, while the second maximum is matched if at least two Si–N bonds are involved