A new high-pressure modification of Nb2O5

The transformation of H-Nb2O5 has been studied by using a "toroid"-type hig h-pressure chamber at pressures of 5.0 and 8.0 cpa in the temperature regio n 800-1400 degrees C, A mixture of B-Nb2O5 and a new modification of niobiu m pentoxide (denoted Z-Nb2O5) with seven-coordinated niobium was found in t he samples after treatment at P = 8.0 GPa, T = 800-1100 degrees C for 1-10 min, The structure was determined and refined by the Rietveld method from X -ray powder diffraction data. The thermogravimetric analysis showed no redu ction of the sample. (C) 1998 Academic Press.