Long term stability of a modern powder diffractometer

The characteristics of the (101) peak of alpha -quartz and the (104) peak o f the NIST SRM 1976 alumina flat plate standard have been measured in depen dence of time for 60 h with Cu-K alpha (1) radiation in Bragg-Brentano geom etry with a Philips X'Pert diffractometer equipped with a primary Ge(111) m onochromator. It was found that the reproducibility of the peak position an d the peak shape falls well in the +/- 3 sigma range, whereas the peak inte nsity strongly depends on the power history of the X-ray generator and the temperature of the diffraction system. The effects on Rietveld refinements are discussed and recommendations are given for optimized data collection. (C) 2001 International Centre for Diffraction Data.