Local Viscosity of Si‐O‐C‐N Nanoscale Amorphous Phases at Ceramic Grain Boundaries

Internal friction characterization has been used to quantitatively assess the viscosity characteristics of Si‐O‐C‐N glasses segregated to nanometer‐sized grain boundaries of polycrystalline Si ₃ N ₄ and SiC ceramics. A relaxation peak of internal friction, which arises with rising temperature from the viscous sliding of glassy grain boundaries, was systematically collected and analyzed with respect to its shift upon changing the oscillation frequency. As a result of such an analysis, both activation energy for viscous grain‐boundary flow and inherent viscosity of the intergranular glass film could be quantitatively evaluated. Two main features are shown: (i) the presence of N and/or C greatly affects the viscosity characteristics of SiO ₂ phases at Si ₃ N ₄ and SiC grain boundaries; and (ii) the internal friction method has potential as a unique experimental tool for understanding the local properties of nanoscale amorphous phases in new ceramic materials.