Thermal and mechanical properties of glass-like high-entropy rare-earth niobate ceramics

With the pursuit of higher operating temperatures and longer service lifetimes in aero-engines and gas turbines, thermal barrier coatings (TBCs) are facing increasingly stringent requirements in thermal and mechanical performance. Guided by the principle of entropy engineering, two high-entropy rare-earth niobate ceramics, (Lu 0.2 Gd 0.2 Er 0.2 Y 0.2 Yb 0.2 ) 3 NbO 7 (LGEYY) and (Dy 0.2 Gd 0.2 Er 0.2 Y 0.2 Yb 0.2 ) 3 NbO 7 (DGEYY), were successfully synthesized via solid-state reactive sintering. Benefiting from the high configurational entropy, these materials form stable single-phase fluorite-type structures (space group Fm m). The high-entropy effect induces significant lattice distortion and local chemical disorder, which not only suppress grain boundary mobility—leading to excellent sintering resistance and a low grain growth rate (∼0.059 μm/h at 1600 °C)—but also enhances phonon scattering, resulting in glass-like low thermal conductivity (LGEYY: 1.126–1.354 W⋅m -1 ⋅K -1 ; DGEYY: 1.195–1.450 W⋅m -1 ⋅K -1 ) over 25–800 °C. In addition, both ceramics exhibit high thermal expansion coefficients (∼10.6–10.9 × 10 -6 K -1 at 1200 °C), ensuring good thermal compatibility with metallic substrates. LGEYY shows superior mechanical properties (10.924 GPa, 1.486 MPa·m 1/2 ) over DGEYY (10.215 GPa, 1.249 MPa·m 1/2 ), attributed to its finer grains and enhanced lattice energy. Comprehensive performance evaluations indicate that both samples—particularly LGEYY—exhibit a unique combination of low thermal conductivity, high thermal expansion coefficients, and mechanical reliability under extreme thermal conditions, highlighting their potential as next-generation ultra-high-temperature TBCs and offering new insights for the engineering design of high-entropy ceramics.