X-ray and electron microscopy investigation of the topotactic transformation of MoO3 into MoO2

The reduction of MoO3 into MoO2 is investigated by X-ray analysis and electron microscopy from MoO3 (010) platelets between 1000 Å and 5 mm long. In all cases, the following orientation relationship between both lattices is found: [100]2 ∥ [010]3, [122]2 ∥ [100]3, [122]2 ∥ [001]3. MoO3 crystallites twinning and misorientation are discussed in relation with the particular importance of [101]3 directions in MoO3 preserved in the transformation and becoming [010]2 of MoO2. A model for this topotactic reduction is proposed where the reaction develops layer (010)3 by layer (010)3 to form {201}2 type planes in MoO2 structure. Data on the kinetics of the boundary moving in [010]3 direction are also presented.