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Rietveld refinements from an as-obtained rock chunk

Rietveld refinements results, using Rigaku's Ultima IV multipurpose diffraction system, were obtained from a solid rock chunk sample (Figures 1 and 2) composed of six mineral phases. The XRD data was collected in both the parallel and para-focusing beam geometry.

as-obtained rock chunk1
Figure 1: The as-obtained rock chunk sample
as-obtained rock chunk2
Figure 2: The rock chunk sample mounted on the Ultima IV diffractometer

As shown in Figure 3, the rock sample has a highly uneven surface causing the focusing beam data to have both inaccurate peak positions and lower than expected intensities. The shifted peak positions generally arise from a number of displacement errors associated with the sample morphology. Roughness, transparency, and curvature all contribute to the error.

as-btained rock chunk3
Figure 3: Data collected in parallel (PB) and para-focussing modes (BB) on the rock chunk. The zoomed areas and inset show that for the rock chunk PB data (black) has accurate peak position s and better intensity than the BB data (orange).

The use of parallel beam geometry completely circumvents these errors since no focusing is required. The parallel beam data provides accurate peak positions and better intensities as shown in Figure 3. The comparative Rietveld refinement results are shown in Figure 4 and Table 1. It can be seen that better results were obtained with the parallel beam data.

as-obtained rock chunk4
Figure 4: Phase identification and Rietveld refinement on PB and BB data on the rock chunk sample
as-obtained rock chunk5
Table 1: Results of the Rietveld refinement. Better agreement factors were obtained with PB data.