Tiange Bi

Heterostructures, mediated by either weak van der Waals (vdW) coupling or chemical bonding at the heterointerface, can compensate for the inherent shortcomings of individual components and achieve exotic properties through their effective integration. The isoelectronic diamond and boron nitride (BN) can present both cubic and wurtzite polymorphs and hence prospectively form diverse heterostructures. However, synthesizing the metastable hexagonal diamond/wurtzite BN (HD/wBN) covalent heterostructures and clarifying the interfacial chemical bonds remain great challenges, despite considerable effort. In this study, we have demonstrated the direct synthesis of high‐quality HD/wBN covalent heterostructures via structural transformation of graphite/hBN vdW heterostructures under high pressure and high temperature. Raman and structural characterizations evidently confirmed the sharp HD/wBN heterointerface with both C─B and C─N bonds, attributed to inversion domain boundaries within the wBN phase. The mapped pressure‐temperature diagram exhibited the confined window required for HD/wBN heterostructures. Our work provides a viable pathway to prepare various covalent heterostructures through synergistic phase transitions and opens new opportunities for exploring their pronounced properties.

Clathrates are guest/host framework compounds composed of polyhedral cages, yet despite their prevalence among tetrahedral network formers, clathrates with a carbon host lattice remain unrealized synthetic targets. Here, we report a type-I carbon-based framework—a ubiquitous clathrate structure type found throughout compounds containing tetrahedral building blocks. Following a boron-stabilization scheme based on first-principles predictions in the Ca–B–C system at high pressure, type-I Ca ₈ B _x C _{46− x} ( x ≈ 9) was synthesized in the archetypal Pm 3 ¯ n lattice with stability derived from substitutionally disordered boron atoms on hexagonal ring framework positions. The synthesized clathrate, which is recoverable to ambient conditions, expands topological network similarity across tetrahedral systems and opens possibilities for a broad family of diamond-like, carbon-based compounds with tunable properties based on the wide potential for guest/host-atom substitutions and framework versatility.

Designing materials with advanced functionalities is the main focus of contemporary solid-state physics and chemistry. Research efforts worldwide are funneled into a few high-end goals, one of the oldest, and most fascinating of which is the search for an ambient temperature superconductor (A-SC). The reason is clear: superconductivity at ambient conditions implies being able to handle, measure and access a single, coherent, macroscopic quantum mechanical state without the limitations associated with cryogenics and pressurization. This would not only open exciting avenues for fundamental research, but also pave the road for a wide range of technological applications, affecting strategic areas such as energy conservation and climate change. In this roadmap we have collected contributions from many of the main actors working on superconductivity, and asked them to share their personal viewpoint on the field. The hope is that this article will serve not only as an instantaneous picture of the status of research, but also as a true roadmap defining the main long-term theoretical and experimental challenges that lie ahead. Interestingly, although the current research in superconductor design is dominated by conventional (phonon-mediated) superconductors, there seems to be a widespread consensus that achieving A-SC may require different pairing mechanisms. In memoriam, to Neil Ashcroft, who inspired us all.

Tetrahydrides crystallizing in the ThCr₂Si₂ structure type have been predicted to become stable for a plethora of metals under pressure, and some have recently been synthesized. Through detailed first‐principles investigations we show that the metal atoms within these symmetry MH₄ compounds may be divalent, trivalent or tetravalent. The valence of the metal atom and its radius govern the bonding and electronic structure of these phases, and their evolution under pressure. The factors important for enhancing superconductivity include a large number of hydrogenic states at the Fermi level, and the presence of quasi‐molecular H units whose bonds have been stretched and weakened (but not broken) via electron transfer from the electropositive metal, and via a Kubas‐like interaction with the metal. Analysis of the microscopic mechanism of superconductivity in MgH₄, ScH₄ and ZrH₄ reveals that phonon modes involving a coupled libration and stretch of the H units leading to the formation of more complex hydrogenic motifs are important contributors towards the electron phonon coupling mechanism. In the divalent hydride MgH₄, modes associated with motions of the hydridic hydrogen atoms are also key contributors, and soften substantially at lower pressures.