We present the discovery of a novel nitrogen phase synthesized using laser-heated diamond anvil cells at pressures between 120-180 GPa well above the stability field of cubic gauche (cg)-N. This new phase is characterized by its singly bonded, layered polymeric (LP) structure similar to the predicted Pba2 and two colossal Raman bands (at ∼1000 and 1300  cm^{-1} at 150 GPa), arising from two groups of highly polarized nitrogen atoms in the bulk and surface of the layer, respectively. The present result also provides a new constraint for the nitrogen phase diagram, highlighting an unusual symmetry-lowering 3D cg-N to 2D LP-N transition and thereby the enhanced electrostatic contribution to the stabilization of this densely packed LP-N (ρ=4.85  g/cm^{3} at 120 GPa).

High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ∼6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity.extended solids | magnetic ordering | metallization | nonconventional superconductors | non-Fermi liquids H ighly compressed low-Z molecular solids become extended solids in 3D network structures of polymeric and/or metallic states, as found in their periodic high-Z counterparts (1, 2). A relevant question is then, if these extended forms of simple molecular solids can give rise to novel properties such as superconductivity and magnetism, as often found in sp/spd-elemental metals and metallic alloys at low temperatures (3, 4). The theoretical prediction of high-temperature (possibly 300 K) superconductivity in metallic hydrogen at high pressure is stimulating in this regard (5), yet the superconductivity in simple molecular solids has only been observed in paramagnetic oxygen at T C = ∼0.6 K above 100 GPa (6).Recently, we have reported that carbon disulfide undergoes a series of pressure-induced transformations from a transparent molecular solid (Cmca, depicted as phase I) at 2 GPa, to a black polymer of (-S-(C=S)-) p with three-folded carbon atoms bonded to sulfur atoms (CS3 phase or phase II[CS3], signifying the threefold carbon coordination in the bracket) at 10 GPa and then to a highly reflective polymer with four-folded carbons (CS4 phase or III[CS4]) above 40-50 GPa (2). Although highly disordered, phase III[CS4] exhibits a remarkable electrical conductivity of ∼5 μΩ m at ambient temperatures similar to that of an elemental metal (rather than an organic polymer or a polymeric metal) (7). The resistivity ∼5 μΩ m of phase III[CS4] is close to that of elemental metals, such as titanium (0.42 μΩ m), europium (0.94 μΩ m), and intermetallic alloys, such as Nichrome (1.1 μΩ m), Pt/Pd (0.4 μΩ m), rather than organic metals. In the present study, we further show that the phase III[CS4] undergoes a magnetic ordering transition below ∼42 K and enters a superconducting state at ∼6.2 K, both observed over a large pressure range from 50 to 172 GPa (the maximum pressure studied) and exhibits the characteristics of a correlated intermetallic "molecular" alloy. The present results are summarized in the phase diagram...

We present integrated spectral, structural, resistance, and theoretical evidences for simple molecular CS 2 transformations to an insulating black polymer with three-fold carbon atoms at 9 GPa, then to a semiconducting polymer above 30 GPa, and finally to a metallic solid above 50 GPa. The metallic phase is highly disordered 3D network structure with four-fold carbon atoms at the carbon-sulfur distance of ~1.70Å. Based on first principle calculations, we present two plausible structures for the metallic phase: α-chalcopyrite and tridymite, both of which exhibit metallic ground states and disordered diffraction features similar to that measured. We also present the phase/chemical transformation diagram for carbon disulfide, showing a large stability field of the metallic phase to 100 GPa and 800 K.

The application of pressure, internal or external, transforms molecular solids into extended solids with more itinerant electrons to soften repulsive interatomic interactions in a tight space. Examples include insulator-to-metal transitions in O(2), Xe and I(2), as well as molecular-to-non-molecular transitions in CO(2) and N(2). Here, we present new discoveries of novel two- and three-dimensional extended non-molecular phases of solid XeF(2) and their metallization. At approximately 50 GPa, the transparent linear insulating XeF(2) transforms into a reddish two-dimensional graphite-like hexagonal layered structure of semiconducting XeF(4). Above 70 GPa, it further transforms into a black three-dimensional fluorite-like structure of the first observed metallic XeF(8) polyhedron. These simultaneously occurring molecular-to-non-molecular and insulator-to-metal transitions of XeF(2) arise from the pressure-induced delocalization of non-bonded lone-pair electrons to sp(3)d(2) hybridization in two-dimensional XeF(4) and to p(3)d(5) in three-dimensional XeF(8) through the chemical bonding of all eight valence electrons in Xe and, thereby, fulfilling the octet rule at high pressures.

Under pressure: An increase in the ionic character in CO bonds at high pressures and temperatures is shown by the chemical/phase transformation diagram of CO2 (see picture). The presence of carbonate carbon dioxide (i‐CO2) near the Earth′s core–mantle boundary condition provides insights into both the deep carbon cycle and the transport of atmospheric CO2 to anhydrous silicates in the mantle and iron core.