Room-temperature superconductivity has been a long-held dream and an area of intensive research. Recent experimental findings of superconductivity at 200 K in highly compressed hydrogen (H) sulfides have demonstrated the potential for achieving room-temperature superconductivity in compressed H-rich materials. We report first-principles structure searches for stable H-rich clathrate structures in rare earth hydrides at high pressures. The peculiarity of these structures lies in the emergence of unusual H cages with stoichiometries H_{24}, H_{29}, and H_{32}, in which H atoms are weakly covalently bonded to one another, with rare earth atoms occupying the centers of the cages. We have found that high-temperature superconductivity is closely associated with H clathrate structures, with large H-derived electronic densities of states at the Fermi level and strong electron-phonon coupling related to the stretching and rocking motions of H atoms within the cages. Strikingly, a yttrium (Y) H_{32} clathrate structure of stoichiometry YH_{10} is predicted to be a potential room-temperature superconductor with an estimated T_{c} of up to 303 K at 400 GPa, as derived by direct solution of the Eliashberg equation.

The search for stable polymeric nitrogen and polynitrogen compounds has attracted great attention due to their potential applications as high-energy-density materials. Here we report a theoretical prediction of an interesting LiN5 crystal through first-principles calculations and unbiased structure searching techniques. Theoretical calculations reveal that crystalline LiN5 is thermodynamically stable at pressures above 9.9 GPa, and remains metastable at ambient conditions. The metastability of LiN5 stems from the inherent stability of the N5(-) anions and strong anion-cation interactions. It is therefore possible to synthesize LiN5 by compressing solid LiN3 and N2 gas under high pressure and quench recover the product to ambient conditions. To the best of our knowledge, this is the first time that stable N5(-) anions are predicted in crystalline states. The weight ratio of nitrogen in LiN5 is nearly 91%, placing LiN5 as a promising high-energy material. The decomposition of LiN5 is expected to be highly exothermic, releasing an energy of approximately 2.72 kJ·g(-1). The present results open a new avenue to synthesize polynitrogen compounds and provide a key perspective toward the understanding of novel chemical bonding in nitrogen-rich compounds.

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The existence of natural van der Waals gaps in layered materials allows them to be easily intercalated with varying guest species, offering an appealing strategy to optimize their physicochemical properties and application performance. Herein, we report the activation of layered MoO 3 nanobelts via aqueous intercalation as an efficient biodegradable nanozyme for tumor-specific photo-enhanced catalytic therapy. The long MoO 3 nanobelts are grinded and then intercalated with Na + and H 2 O to obtain the short Na + /H 2 O co-intercalated MoO 3À x (NHÀ MoO 3À x ) nanobelts. In contrast to the inert MoO 3 nanobelts, the NHÀ MoO 3À x nanobelts exhibit excellent enzyme-mimicking catalytic activity for generation of reactive oxygen species, which can be further enhanced by the photothermal effect under a 1064 nm laser irradiation. Thus, after bovine serum albumin modification, the NHÀ MoO 3À x nanobelts can efficiently kill cancer cells in vitro and eliminate tumors in vivo facilitating with 1064 nm laser irradiation.

The knowledge of stoichiometries of alkaline-earth metal nitrides, where nitrogen can exist in polynitrogen forms, is of significant interest for understanding nitrogen bonding and its applications in energy storage. For calcium nitrides, there were three known crystalline forms, CaN2, Ca2N, and Ca3N2, at ambient conditions. In the present study, we demonstrated that there are more stable forms of calcium nitrides than what is already known to exist at ambient and high pressures. Using a global structure searching method, we theoretically explored the phase diagram of CaNx and discovered a series of new compounds in this family. In particular, we found a new CaN phase that is thermodynamically stable at ambient conditions, which may be synthesized using CaN2 and Ca2N. Four other stoichiometries, namely, Ca2N3, CaN3, CaN4, and CaN5, were shown to be stable under high pressure. The predicted CaNx compounds contain a rich variety of polynitrogen forms ranging from small molecules (N2, N4, N5, and N6) to extended chains (N∞). Because of the large energy difference between the single and triple nitrogen bonds, dissociation of the CaNx crystals with polynitrogens is expected to be highly exothermic, making them as potential high-energy-density materials.

The negative oxidation state of gold (Au) has drawn a great attention due to its unusual valence state that induces exotic properties in its compounds, including ferroelectricity and electronic polarization. Although monatomic anionic gold (Au(-)) has been reported, a higher negative oxidation state of Au has not been observed yet. Here we propose that high pressure becomes a controllable method for preparing high negative oxidation state of Au through its reaction with lithium. First-principles calculations in combination with swarm structural searches disclosed chemical reactions between Au and Li at high pressure, where stable Li-rich aurides with unexpected stoichiometries (e.g., Li4Au and Li5Au) emerge. These compounds exhibit intriguing structural features like Au-centered polyhedrons and a graphene-like Li sublattice, where each Au gains more than one electron donated by Li and acts as a 6p-element. The high negative oxidation state of Au has also been achieved through its reactions with other alkali metals (e.g., Cs) under pressures. Our work provides a useful strategy for achieving diverse Au anions.

High pressure can fundamentally alter the bonding patterns of light elements and their compounds, leading to the unexpected formation of materials with unusual chemical and physical properties. Using an unbiased structure search method based on particle-swarm optimization algorithms in combination with density functional theory calculations, we investigate the phase stabilities and structural changes of various Li-B systems on the Li-rich regime under high pressures. We identify the formation of four stoichiometric lithium borides (Li(3)B(2), Li(2)B, Li(4)B, and Li(6)B) having unforeseen structural features that might be experimentally synthesizable over a wide range of pressures. Strikingly, it is found that the B-B bonding patterns of these lithium borides evolve from graphite-like sheets in turn to zigzag chains, dimers, and eventually isolated B ions with increasing Li content. These intriguing B-B bonding features are chemically rationalized by the elevated B anionic charges as a result of Li→B charge transfer.

Being a giant bulk Rashba semiconductor, the ambient-pressure phase of BiTeI was predicted to transform into a topological insulator under pressure at 1.7−4.1 GPa [Nat. Commun. 2012, 3, 679]. Because the structure governs the new quantum state of matter, it is essential to establish the high-pressure phase transitions and structures of BiTeI for better understanding its topological nature. Here, we report a joint theoretical and experimental study up to 30 GPa to uncover two orthorhombic high-pressure phases of Pnma and P4/nmm structures named phases II and III, respectively. Phases II (stable at 8.8−18.9 GPa) and III (stable at >18.9 GPa) were first predicted by our first-principles structure prediction calculations based on the calypso method and subsequently confirmed by our high-pressure powder X-ray diffraction experiment. Phase II can be regarded as a partially ionic structure, consisting of positively charged (BiTe) + ladders and negatively charged I − ions. Phase III is a typical ionic structure characterized by interconnected cubic building blocks of Te−Bi−I stacking. Application of pressures up to 30 GPa tuned effectively the electronic properties of BiTeI from a topological insulator to a normal semiconductor and eventually a metal having a potential of superconductivity.