ON THE DETERMINATION OF ACCURATE INTENSITIES FROM POWDER DIFFRACTION DATA .1. WHOLE-PATTERN FITTING WITH A LEAST-SQUARES PROCEDURE

A new algorithm, direct intensity fitting, has been developed which performs a whole-pattern fitting for powder data. The algorithm is related to the fitting technique of Pawley [J. Appl Cryst. 14, 357-361] but does not require start values for the intensities of the individual reflections. Comparative tests show that direct intensity fitting extracts more accurate intensities from a powder diffractogram and reduces the minimum peak distance for accurate data to half of the half-widths. The structure of the superconductor Ba2YCu3O8-x can be solved in a default direct-methods run with direct-intensity-fitting intensities extracted from a normal laboratory powder diffractogram.