POLYMORPHISM OF OXIDE TI3O5

The oxide Ti3O5 has been prepared by reduction of TiO2(as anatase and as rutile) using Ti metal as reductant and vacuum sintering, or by using CO or H2 as reductant. The oxides produced, and also their oxidation products at 650 °C, were examined by X-ray diffraction. Three forms of Ti3O5 were characterized: 1. (a) a form designated as D-type, produced by the hydrogen reduction of anatase, which yielded rutile only on oxidation; 2. (b) a form designated as D'-type, produced by the hydrogen reduction of rutile, which had an apparently similar X-ray diffraction pattern to that of the D-type, but which yielded a mixture of anatase and rutile on oxidation; 3. (c) a form designated as M-type, produced by the vacuum-sintering of TiO2 with Ti metal, which had a different X-ray diffraction pattern but which also yielded a mixture of anatase and rutile on oxidation. Forms (a) and (b) are similar to the previously-claimed high-temperature form of Magn Éli; form (c) is similar to his low-temperature form; the transition temperature is slightly in excess of 100 °C. The D'-type could be derived from the M-type. The D-type could easily be changed into the M-type by cooling from 1350 °C under vacuum. By annealing experiments, the D-type was shown to be a meta-stable form. Some crystallographic considerations concerning the oxidation behaviour of the various polymorphs of Ti3O5 are proposed, also a possible correlation with the various types of compounds having the pseudobrookite structure. © 1969.