The intrinsically low lattice thermal conductivity κ_L is essentially important for thermoelectric technology to maintain large working temperature difference, in order to enlarge the output power. In principle, high density and complex structure at atomic and nano scale are typical features for thermoelectric materials with low lattice thermal conductivities (κ_Ls). However, many 122-phase Zintl compounds with promising thermoelectric properties defy these paradigms. They adopt three relatively simple structures with comparably small mean atomic mass, while these compounds exhibit considerably low lattice thermal conductivities κ_Ls. Herein we unveil the origins of low κ_Ls in 122-phase Zintl compounds, ascribed from the important aspects including atomic constituents, their arrangements and chemical bonding. The coupling between the acoustic branches and low-frequency optical branches, as well as the anisotropic chemical bonding are responsible for the high anharmonicity, favoring for the low phonon velocity and small relaxation time. This work offers a guidance to design high-performance Zintl thermoelectric materials with ultralow lattice thermal conductivity.

固有的低晶格热导率κ _L对于热电技术保持较大的工作温差，以扩大输出功率至关重要。原则上，高密度并且在原子结构复杂和纳米尺度是对于具有低的晶格热导率的热电材料典型特征（κ_大号或多个）。然而，许多具有良好热电特性的 122 相 Zintl 化合物无视这些范式。它们采用三种相对简单的结构，平均原子质量相对较小，而这些化合物的晶格热导率κ _L s相当低。在这里，我们揭开了低κ _L的起源s 在 122 相 Zintl 化合物中，归因于包括原子成分、它们的排列和化学键在内的重要方面。声分支和低频光分支之间的耦合以及各向异性化学键是高非谐性的原因，有利于低声子速度和小弛豫时间。这项工作为设计具有超低晶格热导率的高性能 Zintl 热电材料提供了指导。