Boundary structure, chemical composition and bonding in superplastic tetragonal material was investigated by means of high-resolution electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy and field emission-type transmission electron microscopy. The ceramics which were studied here were doped with various oxides. It was found that there was no amorphous phase at any grain boundary face, but Y was segregated at grain boundary faces with a width of 3 to 5nm across the boundaries. Segregation of Si was also observed and extended over a width of 4 to 6nm across the boundaries of SiO2-doped material. It was found that Mg, Al and Ti were distributed over a width of several nm across the boundaries of samples which were doped with the corresponding oxides. It was shown that electron energy loss spectra from a grain boundary in SiO2-doped zirconia was shifted, by 3 to 4eV, towards the high energy loss side, when compared with data for the grain interior. It was concluded that this indicated that the ionicity of the grain boundary was higher than that of the grain interior, and resulted in a low grain-boundary energy in SiO2-doped zirconia. This agreed well with the fact that the average dihedral angle between grain boundaries in such samples could be as high as 80.

Y.Ikuhara, P.Thavorniti, T.Sakuma: Materials Science Forum, 1997, 243-245, 345-50