Characterisation of nanocrystalline magnesium oxide by X-ray absorption spectroscopy

There are numerous methods of preparing nanocrystalline materials.

Magnesium oxide is an ideal model system on which to

probe the relation of the preparative route and the microstructure.

Using X-ray absorption spectroscopy (XAS) we show that

the sol-gel route can be used to prepare highly crystalline material

provided there is careful control of the calcination conditions.

In the present work this is achieved by calcining at high temperatures

(at least 800 8C). However, this results in grain growth that

can be prevented by the addition of a pinning agent, SiO2,

during the preparation of the sol. The pinned samples maintain

a particle size of 11 nm even after calcining at 1000 8C. Ball-milling

is a common method of preparing nanocrystalline oxides,

however the present work shows that this produces a significant

fraction of amorphous material, the fraction increasing with decreasing

grain size (e.g. 30% for a grain size of 23 nm).