Mixed oxides of the general formula Fe2-xCrxO3 have been prepared by a
coprecipitation-calcination procedure. The precursors contain a cryst
alline goethite-like phase and an amorphous trihydroxide phase if Cr i
s present. Calcination for 5 h at 673 K resulted in crystalline powder
s whose surface areas decrease from 102 to near 20 M2 g-1 with increas
ing Cr content. IR spectra suggest that the structure of these materia
ls consists of a superstructure of the corundum-type lattice of haemat
ite. In parallel with the decrease of surface area, the smallest slit-
shaped pores arising from goethite-to-haematite topotactic decompositi
on progressively disappear. Cr is observed to form chromate species, s
ome of which are exposed on the surface of the calcined materials. The
se species are thought to have a role in the catalytic combustion acti
vity of these materials. The optical behaviour of the powders in the I
R, visible and UV regions is discussed.