Understanding the interplay between lattice dynamics and charge transport is essential for designing high-performance thermoelectric materials. In this work, we systematically investigate the thermoelectric transport properties of Zintl phase ${\mathrm{XInTe}}_2$ (X = Na, K, Rb) based on first-principles calculations. For lattice thermal transport, we apply self-consistent phonon theory (SCP) for the first time in this system and include the bubble diagram correction to accurately capture finite-temperature phonon renormalization. Moreover, the off-diagonal thermal conductivity contribution ${\kappa }_c$ is incorporated into the calculation of lattice thermal conductivity (${\kappa }_L$). Our results show that the enhanced Born effective charge (BEC) and large dielectric constant in ${\mathrm{NaInTe}}_2$ give rise to strong dynamic polarity, which enhances low-frequency phonon scattering through phonon branch softening and leads to a significant reduction in ${\kappa }_L$. In addition, nearly flat mid-frequency phonon branches are mainly associated with localized Na vibrations, exhibiting rattler-like behavior that further strengthens phonon scattering. For electronic transport, we use the amset framework to evaluate carrier transport properties by explicitly considering multiple scattering mechanisms, including grain boundary (MFP), acoustic deformation potential (ADP), ionized impurity (IMP), polar optical phonon (POP), and piezoelectric (PZ) scattering. As a result, p-type ${\mathrm{NaInTe}}_2$ exhibits a maximum $ZT$ of 2.54 at 800 K. When spin-orbit coupling (SOC) is included, the $ZT$ remains as high as 2.02, highlighting its robust thermoelectric performance.

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• Electrical conductivity
• Energy conversion technologies
• Lattice dynamics
• Phonons
• Thermal conductivity
• Thermoelectric effects
• Thermoelectric transport
• Thermoelectrics