ANALYTICAL INVESTIGATION OF RANDOM GRAIN-BOUNDARIES OF ZR-DOPED SINTERED ALPHA-AL2O3 BY TRANSMISSION ELECTRON-MICROSCOPY AND SCANNING-TRANSMISSION ELECTRON-MICROSCOPY

The effects of the Zr doping in fine-grained alumina (alpha-Al2O3) on fine structures are studied. The combination of high-resolution transm ission electron microscopy (HRTEM) and field emission scanning transmi ssion electron microscopy has been a powerful tool for material invest igations and it was employed to investigate grain-boundary structures, chemical composition and chemical bonding of 1000 ppm Zr-doped polycr ystalline alpha-Al2O3. HRTEM revealed that the atomic structure of gra in-boundary regions was not strongly distorted from that of the surrou nding bulk, alpha-Al2O3. It was found that there was no amorphous phas e at any grain boundaries. Energy-dispersive X-ray spectroscopy (EDS) and electron-energy-loss spectroscopy in a dedicated scanning transmis sion electron microscope used for analytical investigations provided s patial difference information about elemental-composition since the el ectron probe size in the scanning transmission electron microscope is as small as 3 Angstrom. It was shown by the EDS that Zr segregated in the grain-boundary regions with the Zr-to-Al atomic ratio of 1.6 +/- 0 .2%. Normalization and subtraction of the matrix spectra from the inte rface spectra yield grain-boundary-sensitive near-edge structure of en ergy-loss near-edge structure (ELNES). Similar features are found for both the O K edge and the Al L-2,L-3 edge ELNES at the boundary. The o rigin of these features is ascribed to the heavily misshapen defects a t the random boundary.