Local viscosity of Si-O-C-N nanoscale amorphous phases at ceramic grain boundaries

Internal friction characterization has been used to quantitatively assess t he viscosity characteristics of Si-O-C-N glasses segregated to nanometer-si zed grain boundaries of polycrystalline Si3N4 and SiC ceramics. A relaxatio n peak of internal friction, which arises with rising temperature from the viscous sliding of glassy grain boundaries, was systematically collected an d analyzed with respect to its shift upon changing the oscillation frequenc y. As a result of such an analysis, both activation energy for viscous grai n-boundary flow and inherent viscosity of the intergranular glass film coul d be quantitatively evaluated. Two main features are shown: (i) the presenc e of N and/or C greatly affects the viscosity characteristics of SiO2 phase s at Si3N4 and SiC grain boundaries; and (ii) the internal friction method has potential as a unique experimental tool for understanding the local pro perties of nanoscale amorphous phases in new ceramic materials.