Chemistry of the Group VB Pentoxides. VI. The Polymorphism of Nb2O5
Abstract
The polymorphism of Nb2O5 has been reinvestigated. Experimental results indicate the definite existence of two modifications and the possible existence of a third. The δ-modification recently reported has been shown to be a poorly crystallized state of the γ-phase. It is proposed that the α- and β-phases are identical, with the β-modification existing as a two-dimensional array. Transformation temperatures were found to be: amorphous to γ 435°, γ to α 830°. The densities are: amorphous 4.36 g./cm.3 at 25°, γ, 5.17 g./cm.3 at 25° and α, 4.55 g./cm.3 at 25°. None of the transformations was reversible. The α-phase was reindexed on the basis of a monoclinic unit cell with a = 21.34 Å., b = 2.816 Å., c = 19.47 Å. and ≮ β = 120°20′ having 14 molecules/unit cell and an X-ray density of 4.52 g./cm.3. The freezing point of Nb2O5 obtained in the study was 1491°. © 1957, American Chemical Society. All rights reserved.