Structure of Ferromagnetic Iron(III) Oxide, gamma -Fe sub 2 O sub 3

摘要

The known concepts of structure are critically discussed. The lattice constants were determined exactly for the following preparations: gamma -Fe sub 2 O sub 3 from Fe sub 3 O sub 4 , gamma -Fe sub 2 O sub 3 from Fe arc, gamma -Fe sub 2 O sub 3 from Fe(CO) sub 5 , a/sub w/ = 8.316 +- 0.004 A, a/sub w/ = 8.333 +- 0.004 A, and a/sub w/ = 8.3 A. This confirms Haegg's value of a/sub w/ = 8.32 A, which differs from previous lattice-constant determinations (a/sub w/ = 8.4 A). No significant difference in lattice constant or intensity distribution was found between the ferromagnetic iron(III) oxides prepared by the various methods. Several previously unobserved interferences were found in both the x-ray and electron-beam powder diagrams. These can be assigned only by assuming mixed indices, i.e., lower symmetry, or a larger unit cell. This result is in agreement with findings for the analogous gamma -Al sub 2 O sub 3 . The possible space groups are discussed to the extent permitted by the experimental results. (ERA citation 06:006317)