Band convergence and phonon localization in introducing high thermoelectric performance for Zintl-phase SrLiBi material: A theoretical investigation

Zintl phase materials emerge as promising candidates for thermoelectric (TE) applications on account of the low thermal conductivity and superior electronic transport performance. Based on self-consistent phonon theory, Boltzmann transport theory and first-principles calculations, the crystal structure, thermal and electrical transport, and TE properties of Zintl phase SrLiBi compound have been systematically evaluated in the present work. The SrLiBi compound is a direct band gap semiconductor with a band gap of 0.66 eV, which exhibits multi-valley characteristics in electronic band structure, ensuring a high Seebeck coefficient. The relative regular residual analysis reveals that four-phonon scattering plays a pivotal role in the thermal transport behaviors of SrLiBi compound. The lattice distortion induced by Coulomb repulsion around Li atom gives birth to weak Li-Bi bond, and the optical phonon localization from the vibration of Sr atom results in low group velocity and pronounced phonon scattering. Consequently, the Zintl phase SrLiBi compound achieves a low lattice thermal conductivity of 2.59 W m-1K-1 at 300 K in consideration of four-phonon scattering and self-consistent phonon theory. Within consideration of multiple carrier scattering rates, an optimal figure of merit (ZT) of 1.40 at 600 K is achieved for the SrLiBi compound under the carrier concentration of 7 x 1019 cm-3. The current study not only reveals the intrinsic thermal and electronic transport properties of SrLiBi compound, but also highlights the substantial prospect of Zintl phase compounds for TE applications.