Table 2. The main results from combined Rietveld refinements of PXRD and NPD data along with size analyses and obtained stoichiometries from various techniques.
The Rietveld refinements and PDF analyses were carried out based on the atomic structure in space group P43212 with full occupancy on all other sites than Fe 4a. sp-D = refined spherical particle diameter, XPDF = X-ray PDF, NPDF = neutron PDF.
| FL340C | FL390C | FL440C | |
|---|---|---|---|
| Structure (PXRD + NPD) | |||
| a (Å) | 8.3838 (8) | 8.3784 (2) | 8.3846 (4) |
| c (Å) | 8.3452 (10) | 8.3458 (4) | 8.3461 (4) |
| Fe(4) site occupancy fraction | 0.583 (8) | 0.604 (8) | 0.621 (7) |
| Crystallite/particle size | |||
| 〈D PXRD〉 (nm) | 8.81 (9) | 17.4 (3) | 25.4 (3) |
| 〈D superstructure〉 (nm) | 8 (1) | 10 (2) | 10 (3) |
| 〈D (220)〉 (nm) | 9.4 (3) | 19 (1) | 20.5 (6) |
| 〈D TEM〉 (nm) ± standard deviation (nm) | 8.63 (4) ± 2.3 (7) | 20.7 (4) ± 4.0 (7) | 23.0 (3) ± 5.4 (7) |
| 〈sp-D XPDF, phase1〉 (nm) | 11.0 | N/A | 13.4† |
| 〈sp-D XPDF, phase2〉 (nm) | 2.6 | N/A | – |
| 〈sp-D NPDF, nuclear〉 (nm) | 11.0 (2) | 24 (1) | 28 (1) |
| Stoichiometry | |||
| FexO4, x (PXRD + NPD) | 2.791 (4) | 2.802 (4) | 2.811 (3) |
| FexO4, x (X-ray PDF) | 2.70 | N/A | 2.85 |
| FexO4, x (Mössbauer) | 2.69 (6) | 2.71 (2) | 2.71 (3) |
†
PDF sizes of large crystallites are probably underestimated owing to the rapid acquisition PDF (RA-PDF) geometry applied for X-ray total-scattering measurements.