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 7RENbO(4) 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 (6RENbO(4), 2.30-1.40 W m(-1) K-1, 100-1000 degrees C) and higher thermal expansion coefficients (5RENbO(4), 9.03 x 10(-6) K-1, 719 degrees C). These moderate properties indicate a potential materials design for TBCs application. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.