Some new Nb2O5 modifications, metastable oxidation products of NbOsub(x) phases (2.4 < x < 2.5)

The blue-black NbOsub(x) phases (2.4 < x < 2.5) are oxidized metastable in air to colourless (partly yellowish) Nb2O5 modifications already at temperatures about 200 0C. At further heating stepwise and monotropic phase transformations are noticed; as final product the well known stable H modification appears. Some of the 15 new metastable Nb2O5 modifications obtained in this way appear in series. Therewith Nb12O29 (orh. and mon.) changes into two each, Nb22O54 and Nb47O116 into four each, Nb25O62 into two and Nb53O132 into one Nb2O5 phase. During oxidation and the following phase transformations at higher temperatures both the character of single crystal and the principle of building (block structure) of the starting material are maintained. This is especially proven from the electronoptical and X-ray investigations of Nb12O29 (orh. and mon.) and its products obtained by oxidation and further heating. (author)