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 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 (R(BN) = 1.4 Å, Z(BN) = 2.8, Z(NB) = 1.2) by nitrogen and the tetrahedral coordination of silicon (R(SiN) = 1.7 Å, 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 the total pair correlation functions the N-N distances within the boron and silicon coordination polyhedra could be extracted [R(NN)(B = 2.5 Å, R(NN)(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.