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We have determined the complex atomic structure of high‐temperature α‐Ag9GaTe6 phase with a hexagonal lattice (P63mc space group, a=b=8.2766 Å, c=13.4349 Å). The structure has outer [GaTe4]5− tetrahedrons and inner [Ag9Te2]5+ clusters. All of the Ag ions are disorderly distributed in the lattice. Seven types of the Ag atoms constitute the cage‐like [Ag9Te2]5+ clusters. The highly disordered Ag ions vibrate in‐harmonically, producing strong coupling between low frequency optical phonons and acoustic phonons. This in conjunction with a low sound velocity of 1354 m s−1 leads to an ultralow thermal conductivity of 0.20 W m−1 K−1 at 673 K. Meanwhile, the deficiency of Ga in Ag9Ga1−xTe6 compounds effectively optimizes the electronic transport properties. Ag9Ga0.91Te6 attains a highest power factor of 0.40 mW m−1 K−2 at 673 K. All these contribute to a much‐improved ZT value of 1.13 at 623 K for Ag9Ga0.95Te6, which is 41 % higher than that of the pristine Ag9GaTe6 sample. [ABSTRACT FROM AUTHOR]

CuInTe2/graphene composites were fabricated by spark plasma sintering and their thermoelectric properties were investigated. Embedding graphene sheets into CuInTe2 led to decreased thermal conductivity, which can be ascribed to the enhanced phonon scattering by the interface between graphene and the matrix. An improved dimensionless figure of merit (ZT) of 0.40 at 700 K was achieved in a CuInTe2/graphene composite with a mass ratio of 80 : 1. [ABSTRACT FROM AUTHOR]

A deficiency of Ga in wide band‐gap AgGa1‐xTe2 semiconductors (1.2 eV) can be used to optimize the electrical transport properties and reduce the thermal conductivity to achieve ZT > 1 at 873 K. First‐principles density functional theory calculations and a Boson peak observed in the low temperature heat capacity data indicate the presence of strong coupling between optical phonons with low frequency and heat carrying acoustical phonons, resulting in a depressed maximum of Debye frequency in the first Brillouin zone and low phonon velocities. Moreover, the AgTe bond lengths and TeAgTe bond angles increase with rising temperature, leading to a significant distortion of the [AgTe4]7− tetrahedra, but an almost unmodified [GaTe4]5− tetrahedra. This behavior results in lattice expansion in the ab‐plane and contraction along the c‐axis, corresponding to the positive and negative Gruneisen parameters in the phonon spectral calculations. This effect gives rise to the large anharmonic behavior of the lattice. These factors together with the low frequency vibrations of Ag and Te atoms in the structure lead to an ultralow thermal conductivity of 0.18 W m−1 K−1 at 873 K. A significant distortion of the [AgTe4]7− tetrahedra but an almost unchanged [GaTe4]5− tetrahedra in the structure of AgGaTe2 upon heating leads to lattice expansion in the ab‐plane and contraction along the c‐axis, producing a large anharmonicity in the lattice and intrinsic low thermal conductivity. Maximum ZT above 1 is achieved through Ga deficiency in wide band‐gap AgGa1‐xTe2 semiconductors. [ABSTRACT FROM AUTHOR]