Microstructures, thermophysical properties and corrosion behaviours of equiatomic five-component rare-earth monosilicates

Four equiatomic five-component rare earth monosilicates solid solutions were prepared by spark plasma sintering. Two compositions with larger deviation of ionic radii, (Dy0.2Ho0.2Er0.2Tm0.2Yb0.2)2SiO5 and (Dy0.2Ho0.2Er0.2Y0.2Lu0.2)2SiO5, exhibit single-phase structures and homogenous elemental distributions. Extremely low high-temperature thermal conductivities below 1 Wm-1 K-1 and similar coefficients of thermal expansion with SiC were achieved for both compositions. Further, they both displayed good hightemperature stability and high corrosion resistance in water vapor. When exposed to 1400 degrees C, 90%RH water vapor, only slight weight losses were observed for both compositions during the initial half hours, after which almost no further weight losses were observed.