Electron Microscopy of Beta-Beryllia

Abstract

THE development of β-beryllia1 has been observed in the electron microscope. Fine chips of beryllium oxide obtained by grinding single crystals in a mortar and supported on a carbon substrate were examined in an EM–6 electron microscope. Most of the transparent chips fracture along prism planes and these yielded single crystal diffraction patterns which were readily indexed as the normal hexagonal structure of α-beryllia. Transformation to the high-temperature form was accomplished by defocusing the illuminating electron beam and allowing a more intense beam to strike the sample. This develops a finely shattered texture in the crystal. The evidence that the tetragonal structure of β-beryllia is formed is indicated by the appearance of new rings or diffraction spots from β-beryllia that are superimposed on the spot diffraction pattern of single crystal α-beryllia. In particular there are observed the (110) and (310) reflexions of β-beryllia with d-spacings agreeing within experimental error with those previously reported1; simultaneously the (002) of α-beryllia is commonly absent. Occasionally extra diffraction rings appear; these can be indexed if one presumes that beryllium carbide is formed by reaction between the beryllium oxide and the carbon substrate.