Paramagnetic defects in MoO3-revisited

Detailed interpretation of EPR signals appearing in commercial MoO3 upon re duction in vacuo at different temperatures is presented. New O- species in the MoO3 bulk and Mo5+ ions without a molybdenyl bond have been found under such conditions, their intensities depending on temperature and time of re duction. It is argued that formation and stabilization of these unusual spe cies is related to traces of nitrogen impurities. A model of redox processe s occurring in MoO3 upon gradual loss of the lattice oxygen and during reco nstruction of the MoO3 lattice upon reoxidation of reduced MoO3, involving O- species, as an intermediate stage, is suggested.