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Reitveld
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 (Figure 1&2) composed of six
mineral phases. The XRD data was collected in both the parallel and para-focusing
beam geometry.
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Fig. 1 The as-obtained rock chunk sample
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Fig. 2 The rock chunk sample mounted on the Ultima IV
diffractometer
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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.
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Fig. 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
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|
Sample |
Data using parallel beam |
Data using focusing beam |
| Literature data |
Unit cell (Å) |
Residual factors |
Unit cell (Å) |
Residual factors |
Rock sample
phases (below) |
Overall |
R=10.6%
E=8.51% |
|
R=12.91%
E=9.28% |
Silver (Ag)
a=2.93
c=4.79 |
Phase 1 Ag
a=2.933(2)
c=4.782(7) |
R=10.0% |
Phase 1 Ag
a=2.935(3)
c=4.764(10) |
R=11.6% |
Quartz (Alpha) (SiO2)
a=4.9297
c=5.459 |
Phase 2 SiO2
a=4.97(1)
c=5.46(2) |
R=9.77% |
Phase 2 SiO2
a=4.97(3)
c=5.42(6) |
R=11.66% |
Galena (PbS)
a=5.936 |
Phase 3 PbS
a=5.9881(6) |
R=10.22% |
Phase 3 PbS
a=5.9991(8) |
R=11.52% |
Zinc sulfide (ZnS)
a=3.823
c=74.976 |
Phase 4 ZnS
a=3.836
c=74.98(2) |
R=9.75% |
Phase 4 ZnS
a=3.845(3)
c=75.11(7) |
R=12.53% |
Chalcopyrite (CuFeS2)
a=5.2793
c=10.423 |
Phase 5 CuFeS2
a=5.2826(7)
c=10.42(2) |
R=10.52% |
Phase 5 CuFeS2
a=5.2966(9)
c=10.43(2) |
R=11.84% |
Silicon (Si)
a=5.4308 |
Phase 6 Si
a=5.4364(7) |
R=9.81% |
Phase 6 Si
a=5.4182(8) |
R=12.72% |
Table 1: Results of the Rietveld refinement .
Better agreement factors were obtained with PB data.
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Fig. 4 Phase identification and Rietveld
refinement on PB and BB data on the rock chunk sample. |
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