Diatomic site high-entropy engineering boosts thermal properties of RETaO4 for TBC applications

High-entropy ceramics (HECs) are widely studied to boost the properties of various materials, based on the high-entropy effects and high disorders in ionic radius and atomic weights. To further optimize the properties of RETaO 4 (RE is rare-earth) as thermal barrier coatings (TBCs), a diatomic site high-entropy engineering is applied to increase their disorders, subsequently boosting their thermophysical properties. Four RETaO 4 HECs are designed and synthesized in this work, including (Gd 1 ∕ 5 Dy 1 ∕ 5 Ho 1 ∕ 5 Er 1 ∕ 5 Y 1 ∕ 5 ) (Ta 1 ∕ 2 Nb 1 ∕ 2 ) O 4 , (5HECs-1), (Gd 1 ∕ 5 Dy 1 ∕ 5 Ho 1 ∕ 5 Er 1 ∕ 5 Yb 1 ∕ 5 ) (Ta 1 ∕ 2 Nb 1 ∕ 2 ) O 4 , (5HECs-2), (Gd 1 ∕ 6 Dy 1 ∕ 6 Ho 1 ∕ 6 Er 1 ∕ 6 Yb 1 ∕ 6 Y 1 ∕ 6 ) (Ta 1 ∕ 2 Nb 1 ∕ 2 ) O 4 , (6HECs-1), and (Gd 1 ∕ 6 Dy 1 ∕ 6 Ho 1 ∕ 6 Er 1 ∕ 6 Yb 1 ∕ 6 Lu 1 ∕ 6 ) (Ta 1 ∕ 2 Nb 1 ∕ 2 ) O 4 , (6HECs-2). It shows that the thermal conductivity (1.41–1.59 W ⋅ m − 1 ⋅ K − 1 , 9 0 0 ∘ C) is reduced, while thermal expansion coefficients are improved ( TECs = 1 0 . 4 4 – 1 0 . 8 7 × 1 0 − 6 K − 1 at 1 4 0 0 ∘ C), which are better than their single-RE ceramics. Furthermore, Young’s modulus is proportional to their A -site ionic radius, and RETaO 4 HECs have higher modulus than single-RE RETaO 4 and RENbO 4 ceramics. Accordingly, the diatomic site high-entropy engineering is effective in boosting the thermophysical properties of RETaO 4 , and this strategy can be tried in various oxide ceramics.