Thermal Conductivity of ß‐Si3N4: I, Effects of Various Microstructural Factors

Abstract

Calculations based on a simple modified Wiener's model for thermal conductivity of a composite material predict that the thermal conductivity of ß‐Si 3 N 4 decreases quickly as the grain‐boundary film thickness increases within a range of a few tenths of a nanometer and also that it initially increases steeply with increased grain size, then reaches almost constant values. Because of the faceted nature of the ß‐Si 3 N 4 crystal, the “average” grain‐boundary film thickness is much greater than that in equilibrium. The present study demonstrates both theoretically and experimentally that grain growth alone cannot improve the thermal conductivity of ß‐Si 3 N 4 .