About the variable-counting-time techniques in powder diffraction data: their use in EXPO2004

High quality data are essential for crystal structure solution, particularly when Direct Methods instead of Global Optimization Techniques are used. In this work we study the performances of the variable-counting-time techniques in the two crucial steps of the phasing process: decomposition of the full diffraction pattern and direct phasing. The experimental data were collected by a conventional X-ray laboratory diffractometer: they were then submitted to the program EXPO2004 for assessing their usefulness in the phasing process. The results are compared with those obtained by using experimental diffraction data collected via the traditional fixed-counting-time technique under the same experimental conditions.