Thermal properties and oxygen vacancy behaviors for corrosion products of lutetium silicates against CMAS

Rare earth silicates are promising thermal/environmental barrier coatings (T/EBC) materials facing silicon-based ceramic matrix composite substrates and have attracted much attention due to the severe CMAS (CaO–MgO–Al₂O₃–SiO₂) corrosion. Understanding the mechanism of thermal conductivity and oxygen vacancy behavior of their CMAS corrosion products is crucial to evaluate the performance of coatings in post-service stage. In this work, thermal conductivity as well as the stability and migration behaviors of oxygen vacancy of these seven CMAS corrosion products are studied using first-principles calculations. Analysis of their phonon behaviors indicates that low-frequency phonons play an essential role in heat conduction due to their long phonon relaxation times. The predominant oxygen vacancy configurations for these seven products are determined and their temperature dependent concentrations are predicted according to the calculated formation energies. α-CaSiO₃ with low thermal conductivity and high migration energy barriers is suggested to be the potential corrosion product of T/EBC with excellent service performance. These discoveries do not only provide insights into the thermal conductivity and oxygen vacancy behavior of corrosion products, but also are expected to suggest their potential application as advanced T/EBC materials.