Ultra-low thermal conductivity and enhanced mechanical properties of high-entropy rare earth niobates (RE₃NbO₇, RE = Dy, Y, Ho, Er, Yb)

A new entropy-stabilized rare earth niobates (RE₃NbO₇, RE = Dy, Y, Ho, Er, Yb) system with disordered defective fluorite structure was prepared by solid-state method. XRD, Raman and EDS results confirmed the homogeneous distribution and equimolar doping of rare earth cations. High-entropy RE₃NbO₇ ceramics showed smaller grain size compared with single rare earth niobates owing to the sluggish grain diffusion. Due to the increased configuration entropy, (Dy_0.2Ho_0.2Er_0.2Y_0.2Yb_0.2)₃NbO₇ (5RE₃NbO₇) has enhanced mechanical properties (H_v = 9.51 GPa, K_ⅠC = 2.13 MPa m^0.5), a high thermal expansion coefficient (10.2 × 10⁻⁶ K^-1, 1200℃) and ultra-low thermal conductivity (0.724 W m^-1 K^-1, 25℃). These results suggest that the material can be used as a new type of thermal barrier coatings as alternative to yttria-stabilized zirconia.