BiVO4 exhibits a rich structural polymorphism under high pressure where both fergusonite- and zircon-type BiVO4 transform to scheelite and β-fergusonite structures upon compression.

We report a new allotrope of carbon predicted from rst principles simulations. This allotrope is formed in a simulated conversion of two-dimensional polymeric C 60 precursor subjected to uniaxial compression at high temperature. The structure is made up of 240 carbon atoms in an orthorhombic unit cell (termed as o-C 240 ) having a mixed sp 2 /sp 3 hybridization with the ratio of about 1:5. o-C 240 is stable at ambient condition and exhibits superior mechanical performance including optimum Vickers hardness (45 GPa) and fracture toughness (4.10 MPa m 1/3 ), outperforming most of widely used hard ceramics. The electronic structure reveals semiconducting ground state with an indirect band gap of 1.72 eV. The simple reaction pathway could accelerate discovery of this allotrope in laboratory, and the simultaneous occurrence of high fracture toughness, superhardness and semiconductivity is expected to nd applications for this material.

Polymeric allotropes of nitrogen and nitrogen‐rich compounds containing NN single bonds are attractive candidates for high‐energy‐density materials. However, the low kinetic stability of single bond in nitrogen means that these materials have to be synthesized under high pressure and temperature. Recent advances of experimental high‐pressure techniques and computational structure prediction methods have enabled the investigation of many new nitrogen phases and nitrogen‐rich compounds, and some have been successfully synthesized. Some of the recently synthesized materials have been retrieved at ambient conditions, and the large hysteresis warrants further application‐inspired research. This review introduces the important classes of nitrogen‐rich materials ranging from fundamental insight into bonding in nitrogen, to theoretical investigation of hypothetical compounds, and to laboratory realization of these energetic materials in diamond anvil cell. The progressive development of the field is narrated in chronological order, with the emphasis placed on recent progress in the last 2 years.

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