Anomalous peak broadening in high resolution powder diffraction patterns

peak broadening, which depends markedly on the reflection indices, has been observed in high resolution neutron powder patterns. It is postulated that this is due to variations in some of the unit cell parameters. From the lines which remain narrow the cell parameters (or their combinations) which behave normally can be determined. The remaining parameters have been allowed a range of values, and the resulting contribution to the peak width has been calculated. This has been combined with the normal width function of a Rietveld refinement and excellent agreement with the observed neutron patterns has been obtained. The analysis is illustrated by data from RbOD at room temperature and α-PbO. (author) 10 refs., 2 fig., 1 tab