THE ABSOLUTE STRUCTURE OF ULLMANITE, NiSbS

The crystal of ullmanite from Sakhendorf, Siegerland has the lattice constant a0=5.881±0.002Å.. Single crystal investigation confirmed the predicted space group T4-P213 and the crystal structure was established by means of the two dimensional Fourier method. The bond distances found in ullmanite are: Ni-Sb=2.57Å Sb-S=2.40 Ni-S=2.34.These results give the atomic radii for Ni 1.26Å., for Sb 1.32Å. and for S 1.08Å.. The radii of antimony and sulphur found in ullmanite are close to the Huggins' values. Since the three fold axis of the crystal is polar, the determination of the absolute structure of the crystal was also carried out. With the aid of the anomalous X-ray scattering of Zn Kα radiation by Ni atoms, correlation of the crystal structure of the crystal to the external form was made.