The system chromium trifluoride-niobium pentoxide and defect structures

The system CrF3-Nb2O5 has been examined by the methods of lattice imaging electron microscopy, in the expectation that Cr3+ and F- would build into the ReO3-derived structure to generate compounds analogous to those found in the system WO3-Nb2O5. For three compositions studied (CrF3:Nb2O5 = 1:1, 1:6 and 4:13), the chief product was isostructural with N-Nb2O5. X-ray ultra microprobe analysis of crystalline regions, completely characterized by electron diffraction and lattice imaging, confirmed that the Cr:Nb ratio agreed with the made-up composition, and the product is a solid solution phase Crsub(X)Nbsub(16-X)Osub(40-2X)Fsub(2X). Fluorine was lost during preparation by a pyro-hydrolysis reaction. No analogues of the WO3-Nb2O5 compounds were found, and the N-Nb2O5 solid solutions were notably free from laminar intergrowths of other block structures. However, they contained disordered domains representing fluctuations of composition, with defect structures of types not hitherto observed. These unambiguously indicated local enrichment in CrF3, resisting prolonged annealing. (author)