EFFECT OF HIGH-ANGLE DIFFRACTION DATA ON RIETVELD STRUCTURE REFINEMENT

By utilizing the powder X-ray step-scanning diffraction data of PbSO₄, we have studied the effect of the diffraction data (with different high-angle upper-limit: 2\theta_m= 160,140,120,100,80, 70 and 60°) on the precision of the Rietveld refined lattice constants, structure parameters, and agreement indices. Tbese refined results are compared with those obtained from the single crystal data. It is revealed that the deviations of the refined lattice constants, atomic positions and isotropic temperature factors decrease, and agreement indices become smaller With the increase of 2\theta_m. But when 2\theta_m> 120°, the deviations and agreement indices decrease very slowly. Therefore, in general cases, 2\theta_m should be taken to be 120°or larger in order to get satisfactory refined results in the Rietveld crystal structure refinement.