Epitactic formation of forsterite on MgO single crystals during vacuum annealing

Specimens of {0 0 1} MgO, prepared for analysis in the transmission electron microscope (TEM), have been heated in situ in a conventional TEM in order to study the effect of different heat treatments on the surface of the MgO specimens. A previous study, using a similar in situ heat treatment of MgO, found that at elevated temperatures (∼500 K) a film of different structure and composition formed on the surface of the sample. The previous study concluded that the composition and structure corresponded to that of MgO2. In the present study, similar results to those shown previously have been found. However, the interpretation of these results is quite different. The films are shown to be of a composition and crystal structure that is consistent with forsterite, Mg2SiO4. The films can form as a result of contamination during the high-temperature in situ annealing process.