High‐entropy rare earth titanates with low thermal conductivity designed by lattice distortion

Abstract High‐entropy single‐phase rare earth titanates (RE 0.2 Gd 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 2 Ti 2 O 7 (RE = Sm, Y, Lu) were designed and synthesized successfully, in which their lattice distortion was quantitatively described by mass disorder and size disorder. It is worth mentioning that (Y 0.2 Gd 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 2 Ti 2 O 7 could obtain the low thermal conductivity (1.51 W·m −1 ·K −1 , 1500°C), high thermal expansion coefficient (average, 11.69×10 −6 K −1 , RT ∼1500°C) and excellent high‐temperature stability. In addition, the relationship between the microstructure and thermal transport behaviors has been studied at the atomic scale. Due to the disorder of A‐site ions, severe lattice distortion occurred in specific crystal planes, and the large mass difference between Y 3+ and other RE 3+ further causes mass fluctuation and results in lower thermal conductivity. Compared with YSZ, the high‐entropy rare earth titanate (Y 0.2 Gd 0.2 Ho 0.2 Er 0.2 Yb 0.2 ) 2 Ti 2 O 7 has lower thermal conductivity, higher thermal expansion coefficient, and excellent high‐temperature stability, which has great potential for application in the thermal protection field.