The thermal phonon transport is a key matter for heat managing in materials science which is crucial for device miniaturization and power density increase. Herein, we report the synthesis, structure and characterization of a new compound, Cs₂Ge₃Ga₆Se₁₄, with a unique anisotropic structure simultaneously containing Ge³⁺ and Ge²⁺ that adopt (Ge1)³⁺₂Se₆ dimer or (Ge2)²⁺Se₆ octahedron, respectively. The thermal conductivity was measured to be 0.57–0.48 W m⁻¹ K⁻¹ from 323 to 773 K, the lowest value among all the known Ge containing compounds, approaching its glass limit according to the Cahill’s formulation. More importantly, we discover for the first time that the vibration uncoupling of Ge with different valence states hinders the effective thermal energy transport between the (Ge1)³⁺₂Se₆ dimer and (Ge2)²⁺Se₆ octahedron, and consequently lowers the thermal conductivity. In addition, we propose a structure factor f_i = sin(180 − β) × d_Ge−Q/l_i (i = A, B), with which a structure map of the Cs₂Ge₃M₆Q₁₄ family is given.

热声子传输是材料科学中进行热量管理的关键问题，这对于器件的小型化和功率密度的提高至关重要。在此，我们提出一个新的化合物的合成，结构和特性，铯₂葛₃镓₆硒₁₄，同时与含Ge独特的各向异性结构³⁺和Ge ²⁺的是采用（Ge1的）³⁺ ₂硒₆二聚体或（Ge2）²⁺ Se ₆八面体。测得的热导率为0.57–0.48 W m ^-1 K ^-1从323 K到773 K，这是所有已知的含Ge化合物中的最小值，根据Cahill的公式接近其玻璃极限。更重要的是，我们首次发现具有不同价态的Ge的振动解耦阻碍了（Ge1）³⁺ ₂ Se ₆二聚体和（Ge2）²⁺ Se ₆八面体之间的有效热能传输，从而降低了导热系数。另外，我们提出了一个结构因子f _i = sin（180- β）× d _Ge-Q / l _i（i = A，B），利用该因子Cs ₂的结构图给出了Ge ₃ M ₆ Q ₁₄族。