Vacancies tailoring lattice anharmonicity of Zintl-type thermoelectrics

JF Zhu and QY Ren and C Chen and C Wang and MF Shu and M He and CP Zhang and MD Le and S Torri and CW Wang and JL Wang and ZX Cheng and LS Li and GH Wang and YX Jiang and MZ Wu and Z Qu and X Tong and Y Chen and Q Zhang and J Ma, NATURE COMMUNICATIONS, 15, 2618 (2024).

DOI: 10.1038/s41467-024-46895-4

While phonon anharmonicity affects lattice thermal conductivity intrinsically and is difficult to be modified, controllable lattice defects routinely function only by scattering phonons extrinsically. Here, through a comprehensive study of crystal structure and lattice dynamics of Zintl-type Sr(Cu,Ag,Zn)Sb thermoelectric compounds using neutron scattering techniques and theoretical simulations, we show that the role of vacancies in suppressing lattice thermal conductivity could extend beyond defect scattering. The vacancies in Sr2ZnSb2 significantly enhance lattice anharmonicity, causing a giant softening and broadening of the entire phonon spectrum and, together with defect scattering, leading to a similar to 86% decrease in the maximum lattice thermal conductivity compared to SrCuSb. We show that this huge lattice change arises from charge density reconstruction, which undermines both interlayer and intralayer atomic bonding strength in the hierarchical structure. These microscopic insights demonstrate a promise of artificially tailoring phonon anharmonicity through lattice defect engineering to manipulate lattice thermal conductivity in the design of energy conversion materials.

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