The promising class of the environment-friendly thermoelectrics is the copper-based argyrodite-type ion-conducting crystals exhibiting just extraordinary low thermal conductivity below the glass limit associated with the molten copper sublattice leading to a softening of phonon modes. To explain why the argyrodite structure containing copper ions favors the low thermal conductivity, we have utilized the ab initio calculations of the electron, phonon, and thermoelectric properties of Cu₇PS₆ crystal in the framework of the density functional and Boltzmann transport theories. To obtain the reliable thermoelectric properties of Cu₇PS₆, we take into account the dependence of the electron effective mass m^* on the redundant carrier concentration n. We propose to use the Burstein–Moss effect for the calculation of the electron effective mass m^* of a semiconductor. We have found the strong nonlinear character of copper atom vibrations in Cu₇PS₆ which exceeds substantially the similar values for phosphorous and sulfur atoms. The large vibration nonlinearity of the copper atoms found in Cu₇PS₆ explains the diffusion-like heat transfer and the relatively low coefficient of the lattice thermal conductivity (κ = 0.7 W/(m K)), which is favorable to achieve the large thermoelectric figure of merit.

有前途的环保型热电材料是铜基银铅矿型离子导电晶体，其热导率低于玻璃极限，与熔融铜亚晶格相关，导致声子模式软化。为了解释为什么含铜离子的银铜矿结构有利于低热导率，我们在密度泛函和玻尔兹曼传输理论的框架内利用了Cu ₇ PS ₆晶体的电子、声子和热电性质的从头算计算。为了获得可靠的 Cu ₇ PS ₆热电特性，我们考虑了电子有效质量m ^*关于冗余载流子浓度n。我们建议使用 Burstein-Moss 效应来计算半导体的电子有效质量m ^*。我们已经发现 Cu ₇ PS ₆中铜原子振动的强非线性特征，其大大超过了磷和硫原子的相似值。Cu ₇ PS _{6 中}发现的铜原子的大振动非线性解释了类似扩散的传热和相对较低的晶格导热系数（κ = 0.7 W/(m K)），这有利于实现大的热电品质因数。