Thermal conductivity of beta-Si3N4: I, effects of various microstructural factors

Calculations based on a simple modified Wiener's model for thermal conducti vity of a composite material predict that the thermal conductivity of beta- Si3N4 decreases quickly as the grain-boundary film thickness increases with in a range of a few tenths of a nanometer and also that it initially increa ses steeply with increased grain size, then reaches almost constant values. Because of the faceted nature of the beta-Si3N4 crystal, the "average" gra in-boundary film thickness is much greater than that in equilibrium. The pr esent study demonstrates both theoretically and experimentally that grain g rowth alone cannot improve the thermal conductivity of beta-Si3N4.