The phase problem in neutron diffraction

The structure of any crystal can now be determined ab initio from the neutron Bragg intensity data alone, without recourse to the x-ray structural analysis. This has been made possible by the reduction in data collection times due to the availability of increased neutron fluxes at the samples and the extensive development of the phase determining procedures for neutron diffraction in the last 15 years. In this review, the applications of direct methods, anomalous dispersion techniques and difference Patterson methods are reviewed and it is discussed why these methods are applicable in neutron diffraction. Their limitations are also discussed. Some newer methods like resonance-modulated diffraction and use of 'Renninger effect' to measure the structure invariants are also touched upon. (author)