Disordering of a vanadium monoxide superstructure by electron irradiation

A 200 kV electron microscope has been used to make an in-situ study of disordering by the electron beam of the superstructure V244O320 containing an ordered arrangement of vanadium vacancies. For electron accelerating voltages of 150 kV and above the ordered structure is replaced by the cubic Bl-type containing a random distribution of vanadium vacancies. It is shown that the disordering mechanism involves only the displacement of vanadium atoms by primary incident electrons, giving a value for the vanadium atom displacement energy of 7·8 eV. Observations of the relative rates of decay of the superlattice reflections during disordering show a correlation with the coordination of the vanadium atoms in the structure. A numerical calculation of the expected rates of decay is in good agreement with those observed.