Structural studies on amorphous silicon boron nitride Si3B3N7 : neutron contrast technique on nitrogen and high energy X-ray diffraction

The structure of the new ternary amorphous nitride Si3B3N7, synthesised fro m the single source precursor TADB [(trichlorosilyl)aminodichloroborane], h as been investigated by means of X-ray diffraction using high energy synchr otron radiation and by neutron diffraction using the isotopic contrast tech nique on nitrogen. The X-ray results have been compared with results from e lectron diffraction experiments, confirming the trigonal planar coordinatio n of boron (R-BN = 1.4 Angstrom, Z(BN) = 2.8, Z(NB) = 1.2) by nitrogen and the tetrahedral coordination of silicon (R-SiN = 1.7 Angstrom, Z(SiN) = 3.8 , Z(NSi) = 1.6) by nitrogen. The neutron contrast technique was applied in order to obtain detailed information about the nitrogen environment. From t he total pair correlation functions the N-N distances within the boron and silicon coordination polyhedra could be extracted [R-NN(B) = 2.5 Angstrom, R-NN(Si) = 2.8 Angstrom]. In addition, the difference function shows two di stinct maxima at ca. 3.8 and 4.3 Angstrom 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.