High-entropy rare-earth zirconate ceramics with low thermal conductivity for advanced thermal-barrier coatings

Abstract

The high-entropy rare-earth zirconate ((La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7, 5RE2Zr2O7 HEREZs) ceramics were successfully prepared by a new high-speed positive grinding strategy combined with solid-state reaction method. The microstructure, crystal structure, phase composition, and thermophysical and mechanical properties of the samples were systematically investigated through various methods. Results indicate that the samples have a single-phase defect fluorite-type crystal structure with excellent high-temperature thermal stability. The as-prepared samples also demonstrate low thermal conductivity (0.9–1.72 W·m−1·K−1 at 273–1273 K) and high coefficient of thermal expansion (CTE, 10.9 × 10−6 K−1 at 1273 K), as well as outstanding mechanical properties including large Young’s modulus (E = 186–257 GPa) and high fracture toughness (KIC). Furthermore, the formation possibility of the as-prepared samples was verified through the first-principles calculations, which suggested the feasibility to form the 5RE2Zr2O7 HE-REZs in the thermodynamic direction. Therefore, in view of the excellent multifunctional properties exhibited by the as-prepared 5RE2Zr2O7 HE-REZs, they have great potential applications in next-generation thermal-barrier coatings (TBCs).

Facile synthesis of high-entropy zirconate nanopowders and their sintering behaviors

“…In Refs. [32,33,46], the synthesis of the single-phase HEZ powders always required high temperatures above 1000 ℃. In this work, the HEZ nanopowders can be synthesized at a relatively low temperature of 700 ℃ using the polyacrylamide gel method, which is beneficial for reducing the energy consumption and preparation cost.…”

“…The hardness ( HV ) and fracture toughness ( IC K ) of the HEZ bulks were characterized using the indentation technique, which was performed on a micro-Vickers hardness tester (HV-1000A, Laizhou Huayin, China) with a 1 kgf load and holding time of 15 s. the HV and IC K were calculated by Eqs. ( 1) and ( 2), respectively [32]:…”

“…Among the HECs, highentropy zirconate (HEZ) ceramics with a pyrochlore or defect-fluorite crystal structure have attracted increasing research interests due to their ultra-low thermal conductivity, high coefficient of thermal expansion, excellent irradiation resistance, and outstanding structural stability, which have promising applications in thermal barrier coating and nuclear waste immobilization [28][29][30][31][32][33]. For instance, Liu et al [32] reported that (La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Yb 0.2 ) 2 Zr 2 O 7 demonstrated the low thermal conductivity of 0.9-1.72 W•m −1 •K −1 at 273-1273 K and high coefficient of thermal expansion (10.9×10 −6 K −1 at 1273 K). Li et al [33] found that the thermal conductivity of (5RE 1/5 ) 2 Zr 2 O 7 (RE = La, Nd, Sm, Eu, Gd, and Y) HECs was below 1 W•m -1 •K -1 in the temperature range of 300-1200 ℃.…”

Improved wear resistance and low thermal radiative conductivity of a middle‐entropy tantalate Y0.5Gd0.5Ta0.5Nb0.5O4

“…Entropy engineering is realized by multiple elements forming multi‐principal materials with equal molar ratio or nearly equal molar ratio. Entropy engineering can increase the configuration entropy of materials, significantly reduce the thermal conductivity, and improve the mechanical properties of materials 26–29 . The reports about entropy engineering and its effects on thermophysical properties of YTaO 4 are limited, and we synthesize and study a middle‐entropy ceramic of YTaO 4 , that is, Y 0.5 Gd 0.5 Ta 0.5 Nb 0.5 O 4 (YGTN), in this work.…”

“…Entropy engineering can increase the configuration entropy of materials, significantly reduce the thermal conductivity, and improve the mechanical properties of materials. [26][27][28][29] The reports about entropy engineering and its effects on thermophysical properties of YTaO 4 are limited, and we synthesize and study a middle-entropy ceramic of YTaO 4 , that is, Y 0.5 Gd 0.5 Ta 0.5 Nb 0.5 O 4 (YGTN), in this work. The mechan-ical properties of YTaO 4 were improved by synthesizing YGTN, and the high-temperature thermal radiative conductivity was inhibited.…”