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

Abstract

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.