The symmetry of ordered cubic γ-Fe2O3 investigated by TEM

Abstract

Well-crystallized particles of cubic and tetragonal γ-Fe 2O3 embedded in a Pd matrix were produced besides other oxides by internal oxidation of a Pd-Fe alloy in air. Particles of tetragonal γ-Fe2O3 consist of orientation domains with the c axes normal to each other. Particles of the ordered cubic γ-Fe 2O3 appear single crystalline in bright field and in dark field images with reflections of the basic spinel structure. In dark field images enantiomorphous domains were observed using reflections of the ordered phase. From the analysis of electron diffraction patterns in the principal zone axes the description of ordered cubic γ-Fe2O3 in the enantiomorphous space groups P4132/P4332 follows without further presumptions. In the sequence from space group Fd3̄m of disordered cubic γ-Fe2O3 via P4132/P4332 of the ordered cubic phase to the pair P41212/P4 3212 of tetragonal γ-Fe2O3 a continuous group-subgroup relation can be derived. This relation shows that ordered cubic γ-Fe2O3 is an intermediate phase upon ordering of vacant octahedral sites towards tetragonal γ-Fe 2O3. © 2006 Verlag der Zeitschrift für Naturforschung.