Free and bound polarons in vanadium pentoxide

ESR and DC conductivity measurements have been performed on a V 2 O 5 single crystal in the temperature range 4-500K. They suggest that, at low temperature, the unpaired electron remains localised on two vanadium sites associated with an oxygen vacancy, leading to the formation of bound polarons characterised by a 15-hyperfine-lines ESR spectrum. As the temperature is raised, bound polarons are free from the electrostatic field of the oxygen vacancies and the electrical properties of the oxide above 300K mainly arise from the hopping of free polarons between vanadium sites that are not associated with oxygen vacancies.