Dependence of magnetization on crystal fields and exchange interactions in magnetite

Enhanced Electrochemical Lithium-Ion Charge Storage of Iron Oxide Nanosheets

“…The structures of Fe 3 O 4 and γ-Fe 2 O 3 are closely related; however, local structure differences provide the basis for differentiating the two phases using vibrational spectroscopy. At room temperature, Fe 3 O 4 belongs to the inverse spinel cubic structure under the O h 7 ( P 4 3 32) point group and consists of two nonequivalent Fe positions in the unit cell: “A” positions (occupied by Fe 3+ ) involve tetrahedral Fe coordination, and “B” positions (equally populated by Fe 3+ and Fe 2+ ions) involve octahedral Fe coordination. , Within the Fe 3 O 4 structure, the presence of Fe 2+ within octahedral sites is more stable as explained by crystal field theory . The space group of γ-Fe 2 O 3 can be identical to that of Fe 3 O 4 or symmetry-reduced from cubic ( P 4 3 32) to tetragonal ( P 4 1 2 1 2 1 ) with vacancy ordering within the structure. , The γ-Fe 2 O 3 structure has cation vacancies either randomly distributed throughout the tetrahedral and octahedral sites or preferentially located on the octahedral sites (as shown in Figure D). , The structure of γ-Fe 2 O 3 can be represented as (Fe 3+ )­[Fe 5/3 3+ □ 1/3 ]­O 4 , where “(Fe 3+ )” refers to tetrahedral coordination, “[Fe 5/3 ]” designates octahedral coordination, and “□” denotes an octahedrally coordinated cation vacancy …”

“…64,65 Within the Fe 3 O 4 structure, the presence of Fe 2+ within octahedral sites is more stable as explained by crystal field theory. 66 The space group of γ-Fe 2 O 3 can be identical to that of Fe 3 O 4 or symmetry-reduced from cubic (P4 3 32) to tetragonal (P4 1 2 1 2 1 ) with vacancy ordering within the structure. 67,68 The γ-Fe 2 O 3 structure has cation vacancies either randomly distributed throughout the tetrahedral and octahedral sites 69 or preferentially located on the octahedral sites (as shown in Figure 1D).…”