Structure and Electronic Properties of Fe2SH3 Compound under High Pressure

Emergent superconductivity in TaO3 at high pressures

Tantalum (Ta) is an interesting transition metal that exhibits superconductivity in its elemental states. Additionally, several Ta chalcogenides (S and Se) have also demonstrated superconducting properties. In this work, we propose the existence of five high-pressure metallic Ta-O compounds (e.g., TaO3, TaO2, TaO, Ta2O, and Ta3O), composed of polyhedra centered on Ta/O atoms. These compounds exhibit distinct characteristics compared to the well-known semiconducting Ta2O5. One particularly interesting finding is that TaO3 shows an estimated superconducting transition temperature (Tc) of 3.87 K at 200 GPa. This superconductivity is primarily driven by the coupling between the low-frequency phonons derived from Ta and the O 2p and Ta 5d electrons. Remarkably, its dynamically stabilized pressure can be as low as 50 GPa, resulting in an enhanced electron-phonon coupling and a higher Tc of up to 9.02 K. When compared to the superconductivity of isomorphic TaX3 (X = O, S, and Se) compounds, the highest Tc in TaO3 is associated with the highest NEF and phonon vibrational frequency. These characteristics arise from the strong electronegativity and small atomic mass of the O atom. Consequently, our findings offer valuable insights into the intrinsic physical mechanisms of high-pressure behaviors in Ta-O compounds.

Predicted structures and superconductivity of LiYHn (n = 5-10) under high pressure

The structures of LiYH_n (n = 5-10) compounds in the pressure range of 0-300 GPa have been extensively explored using the CALYPSO structure prediction method based on the particle swarm optimization algorithm and first-principles calculation. Four stable structures (P2₁/m LiYH₆, C2/c LiYH₈, P1̄ LiYH₉, R3̄m LiYH₁₀) and three metastable phases (Pnma LiYH₆, P1̄ LiYH₈, Immm LiYH₉) were predicted. They all exhibit metallic and superconducting behavior in their respective stable pressure ranges, and the predicted superconducting transition temperature T_c is within 22-109 K when the pressure is greater than 100 GPa. It was found that after doping Li into YH_n (n = 6, 9, 10), the H₂ units in the system increased, the electron-phonon coupling interaction weakened, and T_c decreased when the structural characteristics, electronic density of states distribution, and superconductivity of LiYH_n and YH_n (n = 6, 8, 9, 10) were compared. Systems that have a high density of H_s states and a low number of Y_d states at the Fermi level have stronger electron-phonon coupling (EPC) interactions and higher T_c.

First-Principles Study of High-Pressure Phase Stability and Electron Properties of Be-P Compounds

New, stable stoichiometries in Be-P systems are investigated up to 100 GPa by the CALYPSO structure prediction method. Along with the BeP₂-I4₁/amd structure, we identify two novel compounds of Be₃P₂-P-42₁m and Be₃P₂-C2/m. It should be noted that the Be-P compounds are predicted to be energetically unfavorable above 40 GPa. As can be seen, interesting structures may be experimentally synthesizable at modest pressure. Our results indicate that at 33.2 GPa, the most stable ambient-pressure tetragonal Be₃P₂-P-42₁m transitions to the monoclinic Be₃P₂-C2/m structure. Moreover, the predicted Be₃P₂-P-42₁m and Be₃P₂-C2/m phases are energetically favored compared with the Be₃P₂-Ia-3 structure synthesized experimentally. Electronic structure calculations reveal that BeP₂-I4₁/amd, Be₃P₂-P-42₁m, and Be₃P₂-C2/m are all semiconductors with a narrow band gap. The present findings offer insight and guidance for exploration toward further fundamental understanding and potential applications in the semiconductor field.

Crystal structures and superconductivity of lithium and fluorine implanted gold hydrides under high pressures

The investigations on gold science have been capturing research interest due to its diverse physical and chemical properties. Gold hydrides in the solid state, as a member of the Au compound family, are rare since the reaction of Au with H is hindered in terms of their similar electronegativity. It is expected that Li and F can provide electrons and holes, respectively, to help stabilize gold hydrides under high pressure. Herein, by means of a crystal structural search based on particle swarm optimization methodology accompanied by first-principles calculations, four hitherto unknown Li-Au-H compounds (i.e., LiAuH, LiAu₂H, Li₂Au₂H, and Li₆AuH) are predicted to be stable under compression. Intriguingly, Au-H bonding is found in LiAuH, LiAu₂H, and Li₂Au₂H. As the gold content increases, Au atom arrangements exhibit diverse forms, from the chain in Li₆AuH, the square layer in LiAuH, the network in Li₂Au₂H, and eventually to the coexistence of square and pyramid layers in LiAu₂H. Additionally, Li₆AuH has a unique cage-type lithium structure. Furthermore, electron-phonon coupling calculations show that these Li-Au-H phases are phonon-modulated superconductors with a superconducting critical temperature of 1.3, 0.06, and 0.02 K at 25 GPa and 2.79 K at 100 GPa. In contrast, we also identified two solid F₄AuH and F₆AuH phases with unexpected semiconductivity. They have structural configurations of H-bridged AuF₄ quasi-square components and distorted AuF₆ octahedrons, respectively, and have no gold-to-hydrogen bonds. Our current results indicate that electron doping at suitable concentrations under pressure can stabilize unique gold hydrides, and provide deep insights into the structures, electron properties, bonding behavior, and stability mechanism of ternary Li-Au-H and F-Au-H compounds.

Emerging Yttrium Phosphides with Tetrahedron Phosphorus and Superconductivity under High Pressures

Metal phosphides have triggered growing interest for their exotic structures and striking properties. Hence, within advanced structure search and first-principle calculations, several unprecedented Y-P compounds (e. g., Y₃ P, Y₂ P, Y₃ P₂ , Y₂ P₃ , YP₂ , and YP₃ ) were identified under compression. Interestingly, as phosphorus content increases, P atoms exhibit diverse behaviors corresponding to standalone anion, dumbbell, zigzag chain, planar sheet, crossing chain-like network, buckled layer, three-dimensional framework, and wrinkled layer. Particularly, Fd-3m YP₂ can be viewed as assemblage of diamond-like Y structure and rare vertex-sharing tetrahedral P₄  units. Impressively, electron-phonon coupling (EPC) calculations elucidate that Pm-3m Y₃ P possesses the highest superconducting critical temperature T_c of 10.2 K among binary transition metal phosphides. Remarkably, the EPC of Pm-3m Y₃ P mainly arises from the contribution of low-frequency soft phonon modes, whereas mid-frequency phonon modes of Fd-3m YP₂ dominate. These results strengthen knowledge of metal phosphides and pave a way for seeking superconductive transition metal phosphides.

Pressure-induced Na-Au compounds with novel structural units and unique charge transfer

The exploration of novel intermetallic compounds is of great significance for basic research and practical application. Considering the interesting and diverse attributes of Na and Au, their large electronegative difference, and the unresolved high-pressure Na-Au structures, first-principles swarm-intelligence structural search calculations are employed to explore the potential Na-Au compounds at high pressures. Besides reproducing the known Na-Au compounds, eleven new phases are disclosed, exhibiting several unprecedented Au atomic arrangements, such as rectangular ladder, layer formed by edge-sharing squares, hexahedron framework, and diamond-like skeleton, enriching the understanding of Au chemistry. Moreover, the coordination number of Au can be effectively modulated by controlling Na composition. In the Na-rich compounds (Na₄Au, Na₅Au, and Na₆Au), Au shows a formal charge beyond -2, acting as a 6p-block element, originating from pressure-induced unusual Na 3s or 3p → Au 6p charge transfer. These compounds are metallic, but not superconductive. Moreover, the good agreement between the experimental XRD patterns and the simulated ones allows us to assign the predicted P6/mmm Na₂Au and Fm3[combining macron]m Na₃Au as the experimental structures at 59.6 GPa. Our work indicates that the modulation of pressure and chemical composition is a useful way to stabilize novel intermetallic compounds.

Route to a Superconducting Phase above Room Temperature in Electron-Doped Hydride Compounds under High Pressure

The recent theory-orientated discovery of record high-temperature superconductivity (T_{c}∼250  K) in sodalitelike clathrate LaH_{10} is an important advance toward room-temperature superconductors. Here, we identify an alternative clathrate structure in ternary Li_{2}MgH_{16} with a remarkably high estimated T_{c} of ∼473  K at 250 GPa, which may allow us to obtain room-temperature or even higher-temperature superconductivity. The ternary compound mimics a Li- or electron-doped binary hydride of MgH_{16}. The parent hydride contains H_{2} molecules and is not a good superconductor. The extra electrons introduced break up the H_{2} molecules, increasing the amount of atomic hydrogen compared with the parent hydride, which is necessary for stabilizing the clathrate structure or other high-T_{c} structures. Our results provide a viable strategy for tuning the superconductivity of hydrogen-rich hydrides by donating electrons to hydrides via metal doping. Our approach may pave the way for finding high-T_{c} superconductors in a variety of ternary or quaternary hydrides.

A hypervalent and cubically coordinated molecular phase of IF8 predicted at high pressure

Up to now, the maximum coordination number of iodine is seven in neutral iodine heptafluoride (IF7) and eight in anionic octafluoride (IF8 -). Here, we explore pressure as a method for realizing new hypercoordinated iodine compounds. First-principles swarm structure calculations have been used to predict the high-pressure and T → 0 K phase diagram of binary iodine fluorides. The investigated compounds are predicted to undergo complex structural phase transitions under high pressure, accompanied by various semiconductor to metal transitions. The pressure induced formation of a neutral octafluoride compound, IF8, consisting of eight-coordinated iodine is one of several unprecedented predicted structures. In sharp contrast to the square antiprismatic structure in IF8 -, IF8, which is dynamically unstable under atmospheric conditions, is stable and adopts a quasi-cube molecular configuration with R3[combining macron] symmetry at 300 GPa. The metallicity of IF8 originates from a hole in the fluorine 2p-bands that dominate the Fermi surface. The highly unusual coordination sphere in IF8 at 300 GPa is a consequence of the 5d levels of iodine coming down and becoming part of the valence, where they mix with iodine's 5s and 5p levels and engage in chemical bonding. The valence expansion of iodine under pressure effectively makes IF8 not only hypercoordinated, but also hypervalent.

Phase diagram, stability and electronic properties of an Fe–P system under high pressure: a first principles study

The phase diagram and relative stabilities of Fe–P binary compounds are reliably determined at pressures of up to 400 GPa.

Prediction of superconducting ternary hydride MgGeH6: from divergent high-pressure formation routes

Invigorated by the high temperature superconductivity in some binary hydrogen-dominated compounds, we systematically explored high-pressure phase diagrams and superconductivity of a ternary Mg–Ge–H system usingab initiomethods.