Non-stoichiometric disorder in α-Nb₂O₅ at elevated temperatures

Abstract

The electrical conductivity of polycrystallineα-Nb₂O₅ was determined for the oxygen partial pressure range of 10⁰ to 10⁻²⁰ atm and temperature range 700 to 1150 ° C. The data were found to be proportional to the −1/6th power of the oxygen partial pressure for the oxygen pressure range 10⁻²⁰ to 10⁻⁹ atm, and proportional toPO ^−1/4₂ for oxygen pressures greater than 10⁻⁹ atm. The region of linearity where electrical conductivity varies as the −1/4th power of$P_{O_2 }$ increased as the temperature was decreased. Thermogravimetric measurements were carried out in the temperature range 950 to 1250 ° C. The deviation from stoichiometry inα-Nb₂O₅ (x in Nb₂O_5−x ) as a function of partial pressure of oxygen showed two distinct regions, namely a region with an approximately −1/6th dependence on$P_{O_2 }$ and a region where the deviation was nearly independent of oxygen partial pressure. The electrical conductivity and thermogravimetric data are consistent with the presence of small amounts of acceptor impurities inα-Nb₂O₅.