The polymorphism of the oxide Ti3O5

The oxide Ti 3 O 5 has been prepared by reduction of TiO 2 (as anatase and as rutile) using Ti metal as reductant and vacuum sintering, or by using CO or H 2 as reductant. The oxides produced, and also their oxidation products at 650 °C, were examined by X-ray diffraction. Three forms of Ti 3 O 5 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 TiO 2 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 Eli; 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 Ti 3 O 5 are proposed, also a possible correlation with the various types of compounds having the pseudobrookite structure.