The thermal-electric performance of Bi2O2Se can be significantly improved by application of tensile strain and the Bi2O2Se monolayer has great potential as thermoelectric (TE) material.

The concept of element substitution was introduced with the discovery of classic semiconductors in the early 1930s. While it has been demonstrated as an effective strategy to tune the physical properties of related materials over many decades, it is physically limited to the atomic size mismatch between the dopant and the host. From another perspective, if a complex cluster can be chemically introduced into a system with a similar structure, it can be regarded as the equivalent cluster version of substitution. Complex atomic configurations usually offer more tortuous phonon paths and stronger phonon anharmonicity; however, the phenomenon of complex cluster substitution is generally less studied compared with the traditional element substitution. In this work, we take the first step using density functional theory (DFT) calculations to learn the electrical and thermal transport properties of a 1T phase transition-metal dichalcogenide (TMD) monolayer incorporated with octahedral Au6 clusters, i.e., T-Au6S2. It is found that complex cluster substitution leads to a higher phonon scattering frequency and ultralow lattice thermal conductivity (0.167 and 0.171 W/mK at 700 K along the x axis and y axis). Besides, the introduction of Au6 clusters can effectively optimize the electronic structures, balance the relationship between the Seebeck coefficient and the electrical conductivity, and thus improve the power factor. Consequently, T-Au6S2 exhibits a high thermoelectric figure of merit ZT of 3.75 (3.79) at 700 K along the x axis (y axis). Our work demonstrates that complex cluster substitution is a promising route to improve the TE conversion efficiency for low-dimensional semiconductors.

In recent years, high-entropy alloys have been proposed as potential hydrogen storage materials. Despite a number of experimental efforts, there is a lack of theoretical understanding regarding the hydrogen absorption behavior of high-entropy alloys. In this work, the hydrogen storage properties of a new TiZrHfScMo high-entropy alloy are investigated. This material is synthesized successfully, and its structure is characterized as body-centered cubic. Based on density functional theory, the lattice constant, formation enthalpy, binding energy, and electronic properties of hydrogenated TiZrHfScMo are all calculated. The calculations reveal that the process of hydrogenation is an exothermic process, and the bonding between the hydrogen and metal elements are of covalent character. In the hydrogenated TiZrHfScMo, the Ti and Sc atoms lose electrons and Mo atoms gain electrons. As the H content increases, the <Ti–H> bonding is weakened, and the <Hf–H> and <Mo–H> bonding are strengthened. Our calculations demonstrate that the TiZrHfScMo high-entropy alloy is a promising hydrogen storage material, and different alloy elements play different roles in the hydrogen absorption process.

The high entropy alloy is promising for hydrogen storage, especially in regard to its adjustable hydrogen storage properties. Despite several experimental investigations, there still lacks a detailed atomic-level understanding of the hydrogenation process. In this study, based on first-principles calculations, the hydrogen behaviors and microstructural evolution in high entropy alloy TiZrHfMoNb during the hydrogen absorption are investigated systematically. At low hydrogen content, hydrogen atoms prefer to occupy the octahedral interstitial sites of the BCC phase, which is different from that in BCC pure metals; when the hydrogen content reaches 1.08 wt %, the BCC TiZrHfMoNb hydrides transform into FCC phase, and hydrogen atoms are more favorable to occupy the tetrahedral interstitial sites. Further radial distribution function (RDF) analysis indicates that the enhanced disorder of bonds and decreased lattice distortion of the metal structure destabilize the BCC TiZrHfMoNb hydride and eventually induce the BCC → FCC phase transformation, which is quite different from that in conventional alloys; the difference originates from the severe lattice distortion in high entropy alloy. The phonon spectra of different TiZrHfMoNb hydrides show that the hydride with a H/M ratio of 2 dynamically has a stable lattice, corresponding to a hydrogen storage capacity of 1.94 wt %. The present study demonstrates that the high entropy alloys have unique hydrogen absorption ability, which may advance the related experimental and theoretical studies.

A density functional theory plus Hubbard U method is used to investigate how the incorporation of Pu waste into Gd2Zr2O7 pyrochlore influences its thermo-physical properties. It is found that immobilization of Pu at Gd-site of Gd2Zr2O7 has minor effects on the mechanical and thermal properties, whereas substitution of Pu for Zr-site results in remarkable influences on the structural parameters, elastic moduli, elastic isotropy, Debye temperature and electronic structure. The discrepancy in thermo-physical properties between Gd2−yPuyZr2O7 and Gd2Zr2−yPuyO7 may be a result of their different structural and electronic structures. This study provides a direct insight into the thermo-physical properties of Pu-containing Gd2Zr2O7, which will be important for further investigation of nuclear waste immobilization by pyrochlores.