Nb2O5 nanosize powders prepared by sol-gel - Structure, morphology and dielectric properties

The niobium oxide is currently used in the manufacture of relevant technological components, due to its physical characteristics such as the high dielectric constant, the reduced ignition and the high stability of electrical parameters. Their wide availability in nature and low extraction costs are also significant advantages. However, and as it is known, the properties of the niobium oxide powders are strongly dependent on the raw material and on the synthesis route used. Thus, in the present work, Nb2O5 amorphous powders prepared by the sol-gel technique and their crystalline structures, through a controlled heat-treatment process, were analysedThe sentence 'Thus ... analysed' has been slightly modified for clarity. Please check that the meaning is still correct, and amend if necessary ... The XRD patterns of the powders, heat-treated at temperatures between 400 and 1200 degrees C revealed the formation of niobium oxide in different crystalline structures. In the powders heat-treated at temperatures below 900 degrees C, Nb2O5 with orthorhombic phase was observed while for the heat-treatments above 1000 degrees C the crystalline structure detected was monoclinic. For heat-treatments at intermediate temperatures, those two crystalline phases exist. The Raman and FTIR spectroscopy results sustain the XRD results and analysis. The electrical measurements showed that the sample with monoclinic structure, heat-treated at 1200 degrees C, shows the lowest dc activation energy (E-a(dc) = 39.56 kJ/mol) and the highest dc conductivity (1.49 x 10 (4) S/m at 300 K). The highest dielectric constant was observed in the sample heat-treated at 900 degrees C, which presents Nb2O5 with both orthorhombic and monoclinic phases. Dielectric relaxation phenomenon, observed in the 900 degrees C sample, was related to the presence of the monoclinic structure. (C) 2012 Elsevier B. V. All rights reserved.