Magnetic and structural studies of Cr2O5 and Cr3O8

The infrared spectra, indexed X-ray powder diffraction patterns, magnetic susceptibilities between 80 and 300 K, and electron paramagnetic resonance spectra at 80 and 300 K are reported for Cr2O5 and Cr3O8. The results indicate that both oxides are Cr3+/Cr6+ mixed-valence compounds which contain CrO6 octahedra and CrO4 tetrahedra in different ratios. The valence formula for Cr2O5 is Cr3+2Cr6+4O15 and that of Cr3O8 is Cr3+2Cr6+7O24. The X-ray powder data for Cr2O5 and Cr3O8 could be indexed on the basis of a monoclinic unit cell (a = 12.01(2), b = 8.52(1), c = 9.39(1) Å β = 92.0(1)°) and an orthorhombic unit cell (a = 12.01(7), b = 36.60(7) and c = 3.82(1) Å), respectively.