Sol-gel synthesis and characterization of Nb2O5 powders

Nb2O5 powders were prepared by the sol-gel procedure. Nb(OC2H5)(5) dissolved in ethanol was (a) rapidly hydrolysed by adding a concentrated NH4OH solution, or (b) slowly hydrolysed by adding a small amount of H2O. The Nb2O5 powders were characterized by XRD, DTA/TGA, FTIR spectroscopy and SEM. The initial Nb2O5 powders were amorphous. Upon heating at 300 degreesC of the amorphous powder obtained by the method (a) there was no change as shown by XRD, whereas the amorphous powder obtained by the method (b) and also heated at 300 degreesC contained Nb2O5 (TT-phase) plus an amorphous fraction. The amorphous powders heated at 500 degreesC contained Nb2O5 (TT phase), whereas at 650 degreesC the Nb2O5 (T-phase) was obtained. Crystallite sizes were determined using the Scherrer method. The agreggates of nanosized Nb2O5 were present in amorphous Nb2O5 precursors and upon their heating at 300 degreesC, whereas upon heating at 650 degreesC a porous interconnected microstructure was formed in both preparations, (a) and (b), as shown by SEM. (C) 2004 Elsevier B.V. All rights reserved.