Material-genome perspective towards tunable thermal expansion of rare-earth di-silicates

Optimization of thermal expansion coefficient (CTE) mismatch among constituent rare-earth silicate layers is a critical challenge for the optimal multilayer thermal/environmental barrier coating (T/EBC) architecture for SiCf/SiCm CMCs. In this study, thermal expansion properties for beta-, gamma- and delta-RE2Si2O7 polymorphs are investigated via DFT calculations. The interaction between rare-earth (RE) atoms and neighboring bridging oxygen ((OB)) atoms, as well as the structure of [O3Si-(OB)-Si0(3)] pyrosilicate units are the characteristic gene that controls the positive or negative contribution from low-frequency vibration patterns to the overall phonon anharmonicity, and eventually determine the significantly different CTE of RE2Si2O7 polymorphs. Inspired by the concept of genome modification, gamma-(Dy0.15Y0.85)(2)Si2O7 solid solution is designed and synthesized, which shows notable enhancements of CTE as compared with gamma-Y(2)si(2)O(7). Such tunable CTE could presumably be explained by doping-induced localized lattice distortion around [O3Si-O-B-SiO3] pyrosilicate units, leading to switchable magnitude of negative contribution from low-frequency phonons to thermal expansion.