FRESNEL CONTRAST ANALYSIS OF COMPOSITION CHANGES AND SPACE-CHARGE AT GRAIN-BOUNDARIES IN MULLITE

Grain boundaries in two mullite specimens have been characterised usin g Fresnel contrast analysis in the transmission electron microscope. A ratio of the scattering potential differences Delta V between the gra ins and the grain boundaries in the two specimens was obtained without needing to know the absolute specimen thicknesses of the regions exam ined, The characterisation of a glassy intergranular film in one speci men using energy dispersive X-ray spectroscopy then allowed the magnit ude of Delta V at a crystalline boundary in the second specimen to be determined, For the first time, this scattering potential difference w as interpreted in terms of contributions to the contrast from space-ch arge layers as well as changes in electron scattering factor and densi ty.