Atomic interface structure of superplastic ceramics

Since superplasticity in ceramics strongly depends on the grain boundary characteristics, a promising way to advance the development of superplasticity in ceramics is to control the grain boundary structure. One useful method of controlling grain boundary characteristics is to dope the ceramics with a glass phase or with impurities. Examples of this for superplastic tetragonal zirconia polycrystal and alumina ceramics are shown in this paper. To obtain clear guidelines for designing grain boundary characteristics, we must understand the relationship between superplasticity and grain boundary structure, composition, and bonding state in the ceramics. Several results of grain boundary analyses obtained by high resolution electron microscopy (HREM), energy dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) are presented here to clarify the atomic structure, segregation, and chemical bonding state at grain boundaries in the superplastic ceramics. Theoretical understanding is also important to interpret experimental data quantitatively; we show the result of a first-principles molecular-orbital (MO) calculation for understanding the electron energy loss near edge structure (ELNES) from the grain boundaries.