Improved thermophysical properties of rare-earth monosilicates applied as environmental barrier coatings by adjusting structural distortion with RE-doping

Abstract

Four kinds of quinary high-entropy rare-earth (RE) monosilicates and (Y1-xYbx)2SiO5 have been synthesized by solid-state reaction method. Selected rare-earth oxides of Lu2O3 to Gd2O3 react with silica to form homogeneous monosilicate solid solutions at a sintering temperature of 1773 K for 4 h. Wherein Gd-Si-O transforms from oxy-apatite type to X2-RE2SiO5 with increasing the synthesis temperature from 1573 K to 1773 K. Increasing the rare-earth ion species changes the distortion degrees of [REOm] a little bit. However, it’s more effective to improve the distortion degrees with only introducing Yb3+ into Y3+ sites of Y2SiO5. Stronger distortion of [REOm] improves the high-temperature resistance to thermal deformation, resulting in a lower coefficient of thermal expansion (CTE). Due to the highest distortion degree of [REOm], (Y0.2Yb0.8)2SiO5 exhibits the lowest CTE of 6.78 × 10−6 K−1 at 1473 K. Meanwhile, RE-doping enhances the distortion and phonon scattering, contributing to a lower thermal conductivity.