Enhanced mechanical and thermal properties of ferroelastic high-entropy rare-earth-niobates

A novel class of high-entropy rare-earth-niobates (RENbO4) was synthesized via solid-state reaction method. The XRD Rietveld refinement, Raman, and SEM-EDS results implied that the uniform doped element distribution. Unique ferroelastic domain structure formed by t-m phase transition brings the excellent ductility for RENbO4 ceramics (Poisson's ratios > 0.3), where 7RENbO4 exhibits enhanced mechanical properties (Hv = 4.96±0.08 GPa, KⅠc = 2.05±0.14 MPa•m0.5). Moreover, due to the lattice distortion derived from high-entropy effects, high-entropy rare-earth-niobates present lower thermal conductivity (6RENbO4, 2.30-1.40 W m−1 K−1, 100-1000°C) and higher thermal expansion coefficients (5RENbO4, 9.03 × 10−6 K−1, 719°C). These moderate properties indicate a potential materials design for TBCs application.