Exploration of the low thermal conductivities of γ-Y2Si2O7, β-Y2Si2O7, β-Yb2Si2O7, and β-Lu2Si2O7 as novel environmental barrier coating candidates

Thermal conductivities of γ-Y2Si2O7, β-Y2Si2O7, β-Yb2Si2O7, and β-Lu2Si2O7 were investigated by combined first-principles calculations and experimental evaluation. Theoretical calculation was used to predict the elastic properties, anisotropic minimum thermal conductivities, and temperature dependent lattice thermal conductivities. Experimentally, thermal conductivities of these disilicates were measured from room temperature to 1273 K. In addition, their experimental intrinsic lattice thermal conductivities were determined from the corrected thermal diffusivity data after removing the extrinsic contributions from phonon scattering by defects and thermal radiation. The experimental lattice thermal conductivities match well with the theoretical predictions. Furthermore, Raman spectra of the disilicates was measured and used to estimate the optical phonon relaxation time. The present results clearly disclose the specific material parameters that determine the low thermal conductivity of RE2Si2O7 and may provide guidelines for the optimal thermal conductivity of rare earth disilicates.