Contributions to the investigation of inorganic non-stoichiometric compounds. 15

If in contrast to previous investigations the blue-black NbOsub(x) phases (2.4 < x < 2.5) are not oxidized in air, but in a rarefied oxygen atmosphere or with steam, five further metastable Nb2O5 forms can be obtained in addition to the numerous already known Nb2O5 modifications. Nb12O29 (mon. and orh.) and Nb47O116 lead to one new Nb2O5 form each. Nb22O54 yields two new Nb2O5 modifications. It can be deduced from the thermal behaviour that in addition to unexspected transitions between the known and the new metastable modifications in all cases H-Nb2O5 appears as final product at high temperature. The electron optical investigation of the new oxidation products of Nb12O29 (mon. and orh.) shows that their structures are determined by R-type tunnels as the characteristic structure element. By this they clearly differ from the already known oxidation products. With this for the first time sodium free niobium oxide structures occur whose structural concept is substantially shaped by R-type tunnels which are known from NaNb13O33. (author)