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[Formula: see text]Dy[Formula: see text]Ho[Formula: see text]Er[Formula: see text]Y[Formula: see text](Ta[Formula: see text]Nb[Formula: see text]O 4 , (5HECs-1), (Gd[Formula: see text]Dy[Formula: see text]Ho[Formula: see text]Er[Formula: see text]Yb[Formula: see text](Ta[Formula: see text]Nb[Formula: see text]O 4 , (5HECs-2), (Gd[Formula: see text]Dy[Formula: see text]Ho[Formula: see text]Er[Formula: see text]Yb[Formula: see text]Y[Formula: see text](Ta[Formula: see text]Nb[Formula: see text]O 4 , (6HECs-1), and (Gd[Formula: see text]Dy[Formula: see text]Ho[Formula: see text]Er[Formula: see text]Yb[Formula: see text]Lu[Formula: see text](Ta[Formula: see text]Nb[Formula: see text]O 4 , (6HECs-2). It shows that the thermal conductivity (1.41–1.59 W[Formula: see text]m[Formula: see text]K[Formula: see text], [Formula: see text]C) is reduced, while thermal expansion coefficients are improved ([Formula: see text]–[Formula: see text] [Formula: see text]K[Formula: see text] at [Formula: see text]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.