| Abstract Scope |
Zintl compounds with tunnel structures containing sodium atoms are attracting attention as thermoelectric materials. These sodium atoms excite correlated rattling, which affects lattice phonons and results in low thermal conductivity. In this study, such tin-based Zintl compounds (e.g., Na2+xX2+xSn4−x (X = Al, Ga, In) and Na2ZnSn5) are demonstrated, and the correlated rattling of sodium atoms and the origin of their low thermal conductivity are clarified by experimental and computational analyses. Sodium atoms behave as oscillators along the tunnel, and significant interactions occur between sodium atoms and between sodium atoms and the framework. In these Zintl compounds, a shorter inter-rattler distance leads to a lower thermal conductivity, suggesting that phonon scattering is enhanced by the correlated rattling. These findings provide new insights into the behavior of thermoelectric materials with low thermal conductivity and propose a development strategy for high-performance thermoelectric materials that effectively utilizes correlated rattling phenomena. |