Ce2Ni2Cd--A New Intermediate-Valent Cerium Compound

Oxidation of anosovite at temperatures less than 300°C produces new phases of general composition MnO2n-1, based on unit cell intergrowth of M3O5 and anatase structural elements. The structural principles on which the intergrowth series are based were established by analysis of high-resolution transmission electron microscope images. The structure for the dominant intergrowth phase, with composition M6O11, was refined using the Rietveld method applied to powder X-ray data. This phase has monoclinic symmetry and space group C2/m, with a=9.946(2), b=3.744(2), c=20.994(3) ?, and beta=93.30(1)°. Its structure comprises planar intergrowth of M3O5 compositional blocks with the pseudobrookite-type structure and MO2 compositional blocks with the anatase-type structure, parallel to (001)identical to(001) M3O5identical to (101)an. Alternatively, the structure can be considered as chemically twinned anatase with (101)an as the twin composition plane. The anatase blocks are alternately 2octahedra and 3-octahedra wide along [001]. Local regions corresponding to compositions M5O9 (twinned anatase blocks are 2-octahedra wide) and M7O13 (3-octahedra wide anatase blocks) were also observed in TEM images. The results have relevance to the digestion of high-titania slags (anosovite-rich) in the sulfate-route titania pigment process because high sulfuric acid solubility is maintained after the low-temperature treatment, while the preoxidation of trivalent titanium avoids acid consumption by solution oxidation.