Fluctuating bonding leads to glass-like thermal conductivity in perovskite rare-earth tantalates

Understanding the glass-like thermal conductivity ( K) in simple-composition crystalline materials is critical for the development and design of low-K materials. Here, we report the origin of glass-like low K in binary crystalline tantalates RETa 3 O 9 (RE = Nd, Sm, Eu, Gd) by atomistic simulation. It is found that the low K is mainly due to the rattling effect of RE 3 + cations arising from the large difference in the interatomic bonding between O-RE and O-Ta. The vibrational mode decomposition results reveal that most modes in RETa 3 O 9 fall in the Ioffe-Regel regime and exhibit a strongly diffusive nature due to the fluctuating interatomic force of O-Ta in the TaO 6 octahedron. The dual-phonon model reveals that the vast majority ( > 97%) of heat in RETa 3 O 9 is transported by diffusive modes rather than propagating modes. Consequently, the thermal conduction in RETa 3 O 9 exhibits a unique glass-like nature. Contrary to conventional belief, the optical phonon modes in RETa 3 O 9 play a significant role in thermal conduction. Overall, the new insight into the link between chemical binding and glass-like K serves to the development and design of low-K materials for thermoelectric and thermal management applications. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study reveals the origin of glass-like low K in RETa3O9 through atomistic simulation, which is mainly due to the rattling effect of RE3+ cations and the large difference in interatomic bonding between O-RE and O-Ta. It is also found that in RETa3O9, the majority of heat is transported by diffusive modes rather than propagating modes.