Ternary multicomponent Ba/Mg/Si compounds with inherent bonding hierarchy and rattling Ba atoms toward low lattice thermal conductivity

• Published in: Physical chemistry chemical physics : PCCP 2020-09, Vol.22 (33), p.18556-18561
• Main Authors: Li, Jingyu, Yang, Jinfeng, Shi, Beibei, Zhai, Wenya, Zhang, Chi, Yan, Yuli, Liu, Peng-Fei
• Format: Article
• Language: English
• Subjects: Anharmonicity; Barium; Cations; Chemical bonds; Conductivity; Heat conductivity; Heat transfer; Magnesium; Phonons; Silicon compounds; Stoichiometry; Thermal conductivity; Transport properties; Vibration
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d0cp02792h

Compositional tailoring externally enables the fine tuning of thermal transport parameters of materials using the dual modulation of electronic or thermal transport properties. Theoretically, we examined the lattice dynamics of three particularly ternary representatives with different stoichiometry, BaMgSi, Ba 2 Mg 3 Si 4 , and BaMg 2 Si 2 , and identified the inherent bonding hierarchy and rattling Ba atoms, which were responsible for reducing the lattice thermal conductivity. BaMgSi and Ba 2 Mg 3 Si 4 exhibited inherently ultra-low lattice thermal conductivity of 1.27-0.37 W m −1 K −1 in the range of 300-1000 K due to the bonding hierarchy and rattling Ba atoms. The low-energy optical phonons are overlapping with the acoustic phonons. This is associated with the intrinsic rattler-like vibration of Ba cations and leads to the characteristic in the localization of the propagative phonons and large anharmonicity. Although BaMg 2 Si 2 had a dumbbell-shaped Si-Si covalent and Ba-Si/Mg ionic bonding environment and intrinsic rattler-like vibration of Ba cations, the middle frequency optic phonon branches contribute considerably to the thermal conductivity of the lattice. At the same temperature, compared with BaMgSi and Ba 2 Mg 3 Si 4 , the lattice thermal conductivity of BaMg 2 Si 2 almost doubles owing to the higher phonon lifetime and group velocities. Our findings highlight considerable potential for thermoelectric applications with a different stoichiometric ratio of Ba/Mg/Si systems due to their low lattice thermal conductivities via intrinsic modulating stoichiometry. We investigated the lattice dynamics of three representatives, BaMgSi, Ba 2 Mg 3 Si 4 , and BaMg 2 Si 2 , to identify the inherent bonding hierarchy and rattling Ba atoms that are responsible for reducing lattice thermal conductivity.