Diamond is a prototypical ultrawide band gap semiconductor, but turns into a superconductor with a critical temperature T c ≈ 4 K near 3% boron doping [E. A. Ekimov et al., Nature (London) 428, 542 (2004)]. Here we unveil a surprising new route to superconductivity in undoped diamond by compressionshear deformation that induces increasing metallization and lattice softening with rising strain, producing phonon mediated T c up to 2.4-12.4 K for a wide range of Coulomb pseudopotential μ Ã ¼ 0.15-0.05. This finding raises intriguing prospects of generating robust superconductivity in strained diamond crystal, showcasing a distinct and hitherto little explored approach to driving materials into superconducting states via strain engineering. These results hold promise for discovering superconductivity in normally nonsuperconductive materials, thereby expanding the landscape of viable nontraditional superconductors and offering actionable insights for experimental exploration.
Diamond is the quintessential superhard material widely known for its stiff and brittle nature and large electronic band gap. In stark contrast to these established benchmarks, our first-principles studies unveil surprising intrinsic structural ductility and electronic conductivity in diamond under coexisting large shear and compressive strains. These complex loading conditions impede brittle fracture modes and promote atomistic ductility, triggering rare smooth plastic flow in the normally rigid diamond crystal. This extraordinary structural change induces a concomitant band gap closure, enabling smooth charge flow in deformation created conducting channels. These startling soft-and-conducting modes reveal unprecedented fundamental characteristics of diamond, with profound implications for elucidating and predicting diamond's anomalous behaviors at extreme conditions.
Hydrogen-rich compounds attract significant fundamental and practical interest for their ability to accommodate diverse hydrogen bonding patterns and their promise as superior energy storage materials. Here, we report on an intriguing discovery of exotic hydrogen bonding in compressed ammonia hydrides and identify two novel ionic phases in an unusual stoichiometry NH 7 . The first is a hexagonal R3̅ m phase containing NH 3 −H + −NH 3 , H − , and H 2 structural units stabilized above 25 GPa. The exotic NH 3 −H + −NH 3 unit comprises two NH 3 molecules bound to a proton donated from a H 2 molecule. Above 60 GPa, the structure transforms to a tetragonal P4 1 2 1 2 phase comprising NH 4 + , H − , and H 2 units. At elevated temperatures, fascinating superionic phases of NH 7 with part-solid and part-liquid structural forms are identified. The present findings advance fundamental knowledge about ammonia hydrides at high pressure with broad implications for studying planetary interiors and superior hydrogen storage materials.
An enduring geological mystery concerns the missing xenon problem, referring to the abnormally low concentration of xenon compared to other noble gases in Earth’s atmosphere. Identifying mantle minerals that can capture and stabilize xenon has been a great challenge in materials physics and xenon chemistry. Here, using an advanced crystal structure search algorithm in conjunction with first-principles calculations we find reactions of xenon with recently discovered iron peroxide FeO2, forming robust xenon-iron oxides Xe2FeO2 and XeFe3O6 with significant Xe-O bonding in a wide range of pressure-temperature conditions corresponding to vast regions in Earth’s lower mantle. Calculated mass density and sound velocities validate Xe-Fe oxides as viable lower-mantle constituents. Meanwhile, Fe oxides do not react with Kr, Ar and Ne. It means that if Xe exists in the lower mantle at the same pressures as FeO2, xenon-iron oxides are predicted as potential Xe hosts in Earth’s lower mantle and could provide the repository for the atmosphere’s missing Xe. These findings establish robust materials basis, formation mechanism, and geological viability of these Xe-Fe oxides, which advance fundamental knowledge for understanding xenon chemistry and physics mechanisms for the possible deep-Earth Xe reservoir.
As the prototype of MB6 (M = alkaline-earth and rare-earth metals) compounds, YB6 possesses the highest superconducting critical temperature in this family at the ambient pressure. Here, we performed a first principle exploration on the chemical bonding states and the corresponding electronic properties of YB6 at high pressure. Two phases with Cmcm and I4/mmm space groups are predicted using CALYPSO method, energetically more stable than the previously proposed structures. The B covalent network is eventually evolved from B6 octahedron in the cubic Pm-3m phase to B24 unit in I4/mmm phase. The calculated electron–phonon coupling parameters show that the contribution of B is significantly increased by the high-pressure effect in Cmcm and I4/mmm structure, contrary to that in Pm-3m structure. Further calculations of electron–phonon coupling indicate that the high-pressure phases are likely superconducting with the major contribution by boron phonon vibration.
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