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, K_Ⅰc = 2.05±0.14 MPa• m^0.5). 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.