Electrical Conductivity of Nonstoichiometric α ‐ Nb2 O 5

Abstract

The electrical conductivity of reduced was measured after prior reduction in 10−6 atm of air from 350°–1150°K for both single crystals and sintered specimens. The conductivity of single crystals was found to be exponentially dependent on temperature with an activation energy of 0.9 ev in the range from 1150°–650°K and 0.2 ev in the range from 650°–350°K. The electrical conductivity of sintered specimens was also found to be exponentially dependent on temperature, but only a single activation energy was obtained over the entire temperature range. This activation energy was dependent on defect concentration and varied from 1.0 ev for the smallest degree of reduction to almost zero at the highest degree of reduction where the behavior was essentially that of a degenerate semiconductor. An explanation based on overlapping orbitals of trapped electrons is offered to explain both the dependence of activation energy on defect concentration and the absence of a low‐temperature activation energy in sintered material. Finally, two mechanisms are discussed to explain the observed conductivity of reduced . Comparison of conductivity data and thermoluminescence data tends to favor a model in which two trapped electrons are excited from an oxygen vacancy to the “d” band of the niobium cations.