Thermophysical and mechanical properties of medium-entropy rare-earth zirconate ceramics

High mechanical properties and thermophysical properties are desirable for thermal barrier coatings. In this study, we employed first-principle calculations and solid-state reaction methods to investigate the mechanical and thermophysical properties of medium-entropy rare-earth zirconates (Gd_0.25Eu_0.25RE_0.25Sm_0.25)₂Zr₂O₇(RE = La, Nd, Dy, Er, and Yb). The stability and hardness of the gadolinium zirconate system with medium entropy decreases when multiple atoms randomly occupy the A site. The thermal conductivity of (Gd_0.25Eu_0.25Yb_0.25Sm_0.25)₂Zr₂O₇is the lowest at 0.917 W/(m·K) at 1300 K (Slack model), and the minimum thermal conductivities are 1.019 W/(m·K) (Clark model) and 1.158 W/(m·K) (Cahill model), respectively. The thermal conductivities of the (Gd_0.25Eu_0.25Er_0.25Sm_0.25)₂Zr₂O₇and (Gd_0.25Eu_0.25Yb_0.25Sm_0.25)₂Zr₂O₇ceramics were determined by experiments, with values as low as 1.176 W/(m·K) and 1.194 W/(m·K) at 1273 K, respectively. Moreover, both the calculation and experimental results show that as the ionic radius of the elements in the lattice decreases, the thermal expansion coefficient gradually decreases, with (Gd_0.25Eu_0.25La_0.25Sm_0.25)₂Zr₂O₇having the highest thermal expansion coefficient. These findings indicate that medium-entropy rare-earth zirconates can achieve mechanical and thermophysical properties comparable to those of high-entropy rare-earth zirconates. This work provides ideas for improving the application of rare-earth zirconates as thermal barrier coatings.