X-ray diffraction studies of the spinel series Mg(CrxAl2-x)O₄I. Lattice parameters and structure

Eight polycrystalline samples of the spinel series Mg(CrxAl2-x) O4 with 0<or=x<or=2 have been prepared. The lattice parameters have been determined by the centroid method, and the variation with chromium concentration shows a positive deviation from Vegard's law, in agreement with recent measurements on single crystal material. An analysis of the integrated intensities from each sample shows that the normal spinel structure is maintained throughout the series investigated and that the temperature factor B increases from 0.4 to 1.1AA2 as x ranges from 0 to 2. This effect and other similarities to certain manganese ferrites are interpreted as evidence that the Cr3+ ions are behaving as Jahn-Teller ions.