ACCURATE STRUCTURE-ANALYSIS WITH SYNCHROTRON RADIATION - AN APPLICATION TO BORAZONE, CUBIC BN

An accurate room-temperature structure analysis has been carried out on borazone, cubic BN, using synchrotron radiation. X-ray diffraction data were collected on the five-circle diffractometer at HASYLAB during dedicated runs (3.7 GeV) of DORIS II at a wavelength of lambda = 0.5000 (1) angstrom up to sin-theta/lambda = 1.45 angstrom-1. Comparison with accurate tube data measured with Ag K-alpha radiation [Will, Kirfel & Josten (1986). J. Less. Common Met. 117, 61-71] resulted in a general agreement factor of 0.0135 (0.006 omitting the four lowest-order reflections). Refinements with multipole expansions up to the hexadecapole level yielded R values as low as 0.0046. The final R value of a joint data set, prepared by weighted averaging of tube and synchrotron data, was 0.0077. Ensuing deformation density maps agree well with expectation. The analysis and the refinements of the synchrotron radiation data, as well as the comparison with the X-ray tube data, support our previous findings on cuprite, Cu2O, and corundum, alpha-Al2O3 [Kirfel & Eichhorn (1990). Acta Cryst. A46, 271-284], indicating that high-quality X-ray diffraction data can be obtained at a synchrotron radiation source within normal beam-time allocation.