The estimated values of average grain size (XA), internal porosity (Pi) (%), and therefore, the variation of force constants of the ions existing in tetrahedral and octahedral sites with FWHM of peaks at vibrational bands of octahedral (WO) and tetrahedral (WT) for SFO, SGFCO-1, and SGFCO-2 samples.
| Sample | P i (%) | X A (nm) | k O (N m−1) | k T (N m−1) | k Fe–O (N m−1) | k Fe–O (N m−1) | W O | W T | L O (Å) | L T (Å) | L Fe–O (Å) | L Fe–O (Å) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| SFO | 15.1 | 37.5 | 2288.4 | 2680.2 | 53.8 | 95.8 | 65.5 | 135.0 | 0.1951 | 0.1851 | 0.6809 | 0.5619 |
| SGFCO-1 | 19.1 | 70 | 2235.5 | 2645.2 | 52.6 | 95.2 | 67.8 | 145.1 | 0.1966 | 0.1859 | 0.6862 | 0.5630 |
| SGFCO-2 | 13.6 | 47.9 | 2212.3 | 2595.8 | 51.8 | 94.9 | 62.5 | 144.6 | 0.1973 | 0.1871 | 0.6895 | 0.5636 |