A practical application of experimentally determined X-ray phases applied to the direct method

The experimental method for the direct determination of phases, proposed by Chang [Appl. Phys. (1981), A26, 221-226; Phys. Rev. Lett. (1982), 48, 163-166], utilizing the coherent interaction of diffracted X-ray beams according to the dynamical theory in a three-beam multiple Bragg reflection, is applied to the crystal structure of diamond by using an irregularly shaped crystal on a conventional four-circle single-crystal diffractometer. The phases of three reflections can be derived from the signs of three triplet-phase products which are obtained experimentally from three multiple-reflection line profiles. Using these phases as a starting set for the direct method, the phases of other reflections are obtained. The computing time for the MULTAN program is therefore drastically reduced.