A new estimation method for the intrinsic thermal conductivity of nonmetallic compounds: A case study for MgSiN2, AlN and β-Si3N4 ceramics

A new method for estimating the maximum achievable thermal conductivity of non-electrically conducting materials is presented. The method is based on temperature dependent thermal diffusivity data using a linear extrapolation method enabling discrimination between phonon-phonon and phonon-defect scattering. The thermal conductivities estimated in this way for MgSiN2, AlN and β-Si3N4 ceramics at 300 K equal 28, 200 and 105 W m−1 K−1, respectively in favourable agreement with the highest experimental values of 23, 266 and 106–122 W m−1 K−1. This suggests the general applicability of the proposed estimation method for non-metallic compounds. It is expected that when optic phonons contribute to the heat conduction (as is the case for AlN) the intrinsic thermal conductivity at lower temperatures (e.g. 300 K) is underestimated. However, the reliability and accuracy of the presented ‘easy to use’ estimation method seems to be much better than several other estimation methods. Furthermore the needed input for this method can provide information about which processing parameters should be optimised to obtain the highest thermal conductivity.