Electron paramagnetic resonance investigation of the paramagnetic centres in polycrystalline MoO3

Abstract

The defect MoO₃ was obtained by thermal decomposition of hexakisammonium heptamolybdate in vacuo at 630 K. Different signals present in the EPR spectrum of reduced MoO₃ and those appearing in the course of oxidation, were attributed to Mo⁵⁺ ions in various symmetry, situated in different sites of the MoO₃ lattice. The signal of Mo³⁺ ions with effective spin S= 1/2 was observed in the EPR spectrum of both reduced and reoxidized MoO₃. A hole centre (Mo—O)⁵⁺ was found in reoxidized MoO₃. Various methods of stabilization of reduced molybdenum in the MoO₃ lattice were postulated.