CONTRIBUTIONS TO THE INVESTIGATION OF INO RGANIC NONSTOICHIOMETRIC COMPOUNDS .44. NEW ELECTRON-MICROSCOPIC INVESTIGATION OF THE METASTABLE NB2O5 MODIFICATION OX1C
G. Prinz et R. Gruehn, CONTRIBUTIONS TO THE INVESTIGATION OF INO RGANIC NONSTOICHIOMETRIC COMPOUNDS .44. NEW ELECTRON-MICROSCOPIC INVESTIGATION OF THE METASTABLE NB2O5 MODIFICATION OX1C, Zeitschrift fur anorganische und allgemeine Chemie, 622(9), 1996, pp. 1501-1507
Citations number
25
Categorie Soggetti
Chemistry Inorganic & Nuclear
Journal title
Zeitschrift fur anorganische und allgemeine Chemie
Oxidation of the blue-black NbOx phases (2.4 < x < 2.5) in air or a di
luted oxygen atmosphere leads all together to 21 metastable colourless
(partly yellowish) Nb2O5 modifications. These can be described as com
pounds having block structures like the NbOx phases themselves. At 200
degrees C the oxidation process to the metastable phases proceeds qui
te slowly; at higher temperatures all polymorphs are finally transform
ed to H-Nb2O5. Electron diffraction patterns of the polymorph, which c
an be obtained by heating crystals of Nb22O54 in atmospheric environme
nt at about 200 degrees C (Ox1C), show extra spots in the c direction
compared to Nb22O54: This oxidation product is quite sensitive to the
focused electron beam, so the reduction of the crystals back to Nb22O
54 can only be avoided by reducing its intensity. Finally HRTEM images
of thin crystal areas showing a superstructure were obtained. Compari
ng those characteristic image contrasts to calculated images of differ
ent point defect models one finds, that mainly one point defect is res
ponsible for the superstructure. By migration of one Niobium atom two
interstitial oxygen sites are created. So a structure model can be ach
ieved leading to the formula Nb44O110.