S Gustafsson et al. /Joumal of the European Ceramic Sociery 29(2009)539-550 Thin-foil specimens for TEM were prepared by standard composition of mullite grains and amorphous grain boundary pecimen preparation techniques; mechanical grinding and pol- regions was determined by fine probe eDX point analysis. Ele ishing, dimpling and final ion milling to electron transparency. mental profiles acquired by the EDX system attached to the The microstructures were characterized in a Philips CM200 FEGTEM were used for the evaluation of peak areas in the FEGTEM equipped with a Link ISis energy dispersive X-ray quantification of the EDX spectra Due to the uncertainty in (EDX) system and a Gatan Imaging Filter(GIF). The chemical oxygen quantification, only the relative amounts of aluminum -600nm 0 nm nm 3 nn +600nm 3.5 1.5 1000 3 nI Defocus(nm) Fig. 5. Assessment of grain film thickness in the as-sintered polycrystalline mullite using the defocus Fresnel imaging technique. (a) The underfocussed mage shows a set of dark frin to the grain boundary.(b)At Gaussian focus there are no fringes. (c)The fringe contrast is reversed in the overfocussed image so that two the boundary. (d) By plotting the fringe spacing as a function of defocus and extrapolating the data to Gaussian focus, it is possible to estimate the film thickness to, in this case, approximately 0.75 nmS. Gustafsson et al. / Journal of the European Ceramic Society 29 (2009) 539–550 543 Thin-foil specimens for TEM were prepared by standard specimen preparation techniques; mechanical grinding and pol￾ishing, dimpling and final ion milling to electron transparency. The microstructures were characterized in a Philips CM200 FEGTEM equipped with a Link ISIS energy dispersive X-ray (EDX) system and a Gatan Imaging Filter (GIF). The chemical composition of mullite grains and amorphous grain boundary regions was determined by fine probe EDX point analysis. Ele￾mental profiles acquired by the EDX system attached to the FEGTEM were used for the evaluation of peak areas in the quantification of the EDX spectra. Due to the uncertainty in oxygen quantification, only the relative amounts of aluminum Fig. 5. Assessment of grain boundary film thickness in the as-sintered polycrystalline mullite using the defocus Fresnel imaging technique. (a) The underfocussed image shows a set of dark fringes parallel to the grain boundary. (b) At Gaussian focus there are no fringes. (c) The fringe contrast is reversed in the overfocussed image so that two bright lines delineate the boundary. (d) By plotting the fringe spacing as a function of defocus and extrapolating the data to Gaussian focus, it is possible to estimate the film thickness to, in this case, approximately 0.75 nm