来源：ACS Publications
Equimolar multicomponent xenotime rare-earth phosphates (REPO4), ranging from binary to quaternary REPO4, were synthesized via chemical coprecipitation. The synthesized powders were densified via spark plasma sintering (SPS) at 1500 °C. Their thermal conductivity, coefficients of thermal expansion (CTEs), and resistance to calcium–magnesium–alumina–silicate (CMAS) corrosion were systematically characterized to evaluate their potential as environmental barrier coatings (EBCs) for SiC-based ceramic matrix composites (SiC/SiC CMCs). All REPO4 compositions studied here exhibit CTEs close to SiC/SiC-CMCs. Thermal conductivity depends on cation-size disorder and compositional complexity. Notably, at a constant number of constituent elements, increased cation-size disorder reduces thermal conductivity. Among the quaternary compositions, (Sc1/4Lu1/4Er1/4Y1/4)PO4 exhibits minimal thermal conductivity because of its higher degree of size disorder compared to (Lu1/4Yb1/4Er1/4Y1/4)PO4. The CMAS corrosion test at 1300 °C for 96 h resulted in the formation of a uniform, dense, and continuous reaction layer mainly consisting of Ca8MgRE(PO4)7 and RE2Si2O7 for all REPO4. However, at 1400 °C, the CMAS corrosion behavior of REPO4 differs significantly. Binary and ternary REPO4 exhibit direct CMAS infiltration along the grain boundaries without creating a protective reaction layer, whereas quaternary (4RE0.25)PO4 develops a discontinuous reaction layer and halts the CMAS penetration to some extent. The reduced thermal conductivity and enhanced CMAS corrosion resistance of the quaternary compositions, in particular (Lu1/4Yb1/4Er1/4Y1/4)PO4, compared to their binary (Lu1/2Y1/2)PO4 and ternary (Lu1/3Er1/3Y1/3)PO4 counterparts, imply the potential of quaternary phosphates as promising EBC candidates for SiC/SiC CMCs in high-temperature environments.