Dual role of lone pair electron and rattling vibration in Zintl phase BaCaPb thermoelectric material†

Abstract

The crystal structure, phonon dispersion curves, electronic transport parameters, and thermoelectric (TE) properties of the Zintl phase BaCaPb compound are investigated by first-principles calculations in combination with a two-channel model. The regular residuals analysis demonstrates the crucial role of four-phonon scattering behavior in evaluating the thermal transport properties of the BaCaPb compound on account of the noticeable optical–optical gap. The origin of the rattling vibration behaviour is investigated by the quantitative analysis of chemical bond. The diffusion-like phonons are predominantly influenced by the rattling vibration of the Ba atom in the BaCaPb compound. Moreover, the dual role of the lone electrons in Pb and the rattling vibration of the Ba atom contributes to the ultralow lattice thermal conductivity (1.46 W m⁻¹ K⁻¹@ 300 K) in the BaCaPb compound. In addition, the TE properties of the BaCaPb compound are evaluated in consideration of multiple carrier scatterings, and optimal figures of merit (ZTs) of 1.7 and 1.0 are achieved for the n-type and p-type BaCaPb compounds at 600 K. The present work not only reveals the excellent TE properties of the Zintl phase BaCaPb compound through an in-depth study of their thermal and electronic transport properties, but also adopts a two-channel model for the theoretical design of high-efficiency TE materials.