Structure and Shape of Hematite Particles Obtained by Oxidative Thermolysis of Iron Oxalate Dihydrate: Anisotropic Broadening of X-Ray Diffraction Peaks

Hematite obtained by oxidative thermolysis of iron oxalate dihydrate at temperatures from 320 °C to 680 °C is analyzed by in situ powder X-ray diffraction (XRD) and transmission electron microscopy. XRD patterns of hematite demonstrate the anisotropic broadening of the peaks. The width and difference in the broadening of XRD peaks decrease with increasing annealing temperature. The calculation of XRD patterns based on statistical models of 1D disordered crystals reveals the XRD effects induced by stacking faults (SFs) in anionic and cationic sublattices. It is shown that SFs in the anionic sublattice broaden and shift 012, 104, 024, 018, 214 peaks. In the cationic sublattice, they also broaden the mentioned peaks but do not affect their positions. The width of 110, 113, 116, and 300 peaks does not depend on SFs in the cationic sublattice and is used to determine the particle shape. The anisotropic broadening of XRD peaks is shown to be caused by both particle shape anisotropy and SFs in the cationic sublattice. Average sizes of hematite particles in the [001] direction are approximately 2 times smaller than those in the perpendicular direction. As the temperature increases, the SF concentration gradually decreases from 0.035 °C at 320 °C to 0 °C at 560 °C.