The Ⅳ-Ⅵ compound GeTe is considered as a promising alternative to the toxic PbTe for high-efficiency mid-temperature thermoelectric applications.However,pristine GeTe suffers from a high concentration of Ge vacancies,resulting in an excessively high hole concentration(＞ 1 × 10 21 cm -3 ),which greatly limits its thermoelectric enhancement.To address this issue,CuBiTe 2 alloying is introduced to increase the formation energy of Ge vacancies in GeTe,thereby inhibiting the high carrier concentration.The carrier scattering caused by the electronegativity difference between different elements is suppressed due to the similar electronegativity of Cu and Ge atoms.A relatively high hole mobility is obtained,which ultimately leads to a high power factor.Additionally,by introducing Se as an alloying element at the anionic site in GeTe,dense point defects with mass/strainfield fluctuations are induced.This contributes to the strengthening of phonon scattering,thereby reducing the lattice thermal conductivity from 1.44 W·m -1 ·K -1 for pristine GeTe to 0.28 W·m -1 ·K -1 for Ge 0.95 Cu 0.05 Bi 0.05 Te 0.9 Se 0.15 compound at 623 K.

Zintl compounds have continuously received significant attention, primarily due to their structural characteristics that align with the properties of the electron crystal and phonon glass. In this study, the crystal structure and thermoelectric properties of the quaternary Zintl chalcogenide BaScCuTe3 are investigated. The band structure calculations for BaScCuTe3 reveal a slight energy split of 0.08 eV between the second valence band and the valence band maximum, suggesting the presence of multiband-transport behaviors. Substitution of rare earth Gd for Sc is conducted, which significantly increases the hole concentration from 4.1 x 10(19) cm(-3) to 8.2 x 10(19) cm(-3) at room temperature. Meanwhile, the Seebeck coefficient increases because of the participation of the second valence band. A maximum power factor of 6.56 mu W/cmK-2 at 773 K is obtained, which is 72% higher than that of the pristine sample. Moreover, the lattice thermal conductivity decreases from 0.57 W/mK for BaScCuTe3 to 0.48 W/mK for BaSc0.97Gd0.03CuTe3 at 773 K, owing to the introduction of point-defect scattering. As a result, there is a noteworthy improvement in the thermoelectric figure of merit zT, increasing from 0.44 for the undoped sample to 0.85 for BaSc0.98Gd0.02CuTe3. Considering these findings, BaScCuTe3 exhibits great potential and holds promise for further investigation in the field of thermoelectric materials.

Layered compounds including Bi2Te3, SnSe and BiCuSeO usually exhibit large anharmonicity and thus low lattice thermal conductivity, which are viewed as promising thermoelectric candidates for waste heat harvesting. Quaternary layered LaOBiS2 is an n-type semiconductor constructed by fluorite-type [LaO]+ layers and rock-salt-type [BiS2]- layers. Our results reveal that polycrystalline LaOBiS2 sample features weak anisotropy due to the random arrangement of crystalline grains with nonpreferred-orientation growth. The pristine LaOBiS2 has high intrinsic electrical conductivity and low Seebeck coefficient as a result of a high electron concentration (n = 3.25×1020 cm-3, 300 K) from anionic vacancy. Meanwhile, the total thermal conductivity of LaOBiS2 is as low as 1.10 W m-1 K-1 at 873 K. Cu doping has been performed to improve the thermoelectric properties, which causes the precipitation of Bi, and induces the decrease in both electrical conductivity and the thermal conductivity. Thus, synergistical optimization of the electrical and thermal transport properties have been realized. The maximum zT is 0.24 at 873 K for the sample with dopant Cu of 1%, which is improved by 33% compared with pristine LaOBiS2.

Layered compounds like Bi2Te3 and SnSe are attracting great interest for applications in thermoelectric devices, mainly due to their low lattice thermal conductivity from large anharmonicity. Herein, we report the thermoelectric properties of the quaternary layered compound LaOBiS2, which is a n-type semi-conductor constructed by stacking of fluorite-type [LaO]+ layers and rock-salt-type [BiS2]- layers. Our results reveal that the as-sintered LaOBiS2 sample features weak anisotropy due to the almost random arrange-ment of crystalline grains with nonpreferred-orientation growth. The pristine LaOBiS2 has high intrinsic electrical conductivity and low Seebeck coefficient as a result of a high electron concentration (n = 3.25 x1020 cm-3, 300 K) from anionic vacancy. Meanwhile, the total thermal conductivity of LaOBiS2 is as low as 1.10 W m-1 K-1 at 873 K. Cu-doping improve the overall thermoelectric properties, which induces a decrease in both electrical conductivity and thermal conductivity. The maximum zT is 0.24 at 873 K for the sample with dopant Cu of 1 %, indicating a 33 % increase compared with pristine LaOBiS2. Our work de-monstrates that constructing semiconductors by functional building blocks is an effective approach to design thermoelectric compounds. (c) 2023 Elsevier B.V. All rights reserved.