Low thermal conductivity of Lu4Si2O7N2: Theoretical and experimental studies

Thermal conductivity of bulk and dense oxynitride Lu4Si2O7N2 was measured at various temperatures. Results show that Lu4Si2O7N2 possesses low thermal conductivity and has potential applications as thermal insulation material. Detailed analysis shows that the experimental thermal diffusivity is significantly influenced by defects at low temperature and infrared radiation at high temperature. Therefore, we combined Debye model and Slack's equation to predict the temperature dependent intrinsic lattice thermal conductivity of Lu4Si2O7N2. All parameters indispensable in the calculation (equilibrium crystal structure, second order elastic constants, elastic modulus, Debye temperature, and Grüneisen constant) were predicted with the help of first-principles calculation methods. Finally, factors that influence the thermal conductivity of Lu4Si2O7N2 were discussed and possible explanations for the difference between experimental and theoretical thermal conductivity were illustrated.