Thermal and low energy electron bombardment induced oxygen loss of V 2O 5 single crystals: Transition into V 6O 13

Abstract

Thermal treatment in UHV of clean V 2O 5 single crystals results in homogeneous oxygen loss, involving a rate-limiting surface reaction. Depending upon the pretreatment, aircleaved samples transform topotactically into V 6O 13, or into what we call a phase Q of probable composition V 4O 9 or V 6O 13.5. Low energy electron bombardment of clean UHV-cleaved V 2O 5(010) surfaces produces the transition V 2O 5 → V 6O 13 at room temperature. This effect is attributed to electron beam stimulated reactions. The influence on the transition of carbon-containing impurities is discussed. The nucleation of V 6O 13 on V 2O 5 is explained by a model based on a surface reaction, the rate of which is enhanced by the interaction with contaminating molecules and low energy electron bombardment. The presence of shear planes at the boundary between V 2O 5 and the V 6O 13 nuclei locally enhances the oxygen loss rate and allows the V 6O 13 nuclei to grow into the bulk. The enhanced mobility of the oxygen at these boundaries is thought to influence favorably the oxidation-regeneration rate of the V 2O 5-catalyst.