The effect of secondary sintering additives and/or a post-sintering heat treatment on the semicrystalline atomic structure of the intergranular phase in silicon nitride ceramics was investigated. Three different Yb-doped Si3N4 ceramic compositions were examined using a scanning transmission electron microscope, whereby the intergranular atomic structure was directly imaged with Ångstrom resolution. The resulting high-resolution images showed that the atomic arrangement of the Yb takes very periodic positions along the interface between the intergranular phase and the matrix grains, and that a post-sintering 1250C heat treatment, as well as a change of the secondary sintering additives (Al2O3 instead of SiO2), did not alter the atomic positions of Yb. This result had implications for the understanding of how the mechanical properties of ceramics were influenced by the presence of the nanoscale intergranular phase, and for associated computational modelling of its precise role and atomic structure.

Atomic-Scale Observation of the Grain-Boundary Structure of Yb-Doped and Heat-Treated Silicon Nitride Ceramics. A.Ziegler, M.K.Cinibulk, C.Kisielowski, R.O.Ritchie: Applied Physics Letters, 2007, 91[14], 141906