Conduction bipolarons in low-temperature crystalline WO3-x

Abstract

Conduction electrons in the low-temperature phase of crystalline WO3-x(x>or approximately=0.0001) are found to be paired diamagnetically, forming bipolarons due to joint lattice distortion. They can be dissociated with light in a broad band of wavelengths peaked at 1.1 eV, as monitored by the appearance of W5+ESR and a corresponding change in DC conductivity. The transport activation energy is 0.18 eV in the paired state and decreases upon dissociation. The bipolaron binding energy is larger than 0.36 eV. Separated electrons recombine in a bimolecular process controlled by diffusion in the conduction band.