By using a nano-indentation technique after various heat-treatments, the hardness and Young’s modulus were determined for nominally pure single crystals and for crystals which were doped with H, Li, Ni or Co. The resultant defects were monitored by means of optical absorption spectroscopy. It was found that undoped crystals had a hardness of 9.2GPa. After thermochemical reduction at up to about 2300K under 7atm of Mg vapour, resulting in a deficiency of anions, a hardness 10.4GPa was obtained. This enhancement was attributed to O vacancies. In the case of doped crystals, hardening was observed and was attributed to impurities, point defects, cavities and metallic precipitates. A constant value of 300GPa was found for the Young’s modulus in all cases; thus indicating that the elastic properties were not influenced by impurities or intrinsic defects.

Hardness and Elastic Modulus from Nano-Indentations in Nominally Pure and Doped MgO Single Crystals. D.Cáceres, I.Vergara, R.González, Y.Chen: Philosophical Magazine A, 2002, 82[6], 1159-71