Covalently bonded extended phases of molecular solids made of first- and second-row elements at high pressures are a new class of materials with advanced optical, mechanical and energetic properties. The existence of such extended solids has recently been demonstrated using diamond anvil cells in several systems, including nitrogen, carbon dioxide and carbon monoxide. However, the microscopic quantities produced at the formidable high-pressure/temperature conditions have limited the characterization of their predicted novel properties, including high-energy content. In this paper, we present experimental evidence that these extended low-Z solids are indeed high-energy-density materials, by milligram-scale high-pressure synthesis, recovery and characterization of polymeric CO (p-CO). Our spectroscopic data reveal that p-CO is a random polymer made of lactonic entities and conjugated C=C with an energy content rivalling or exceeding that of HMX (cyclo-tetramethylene tetranitramine, a commonly used conventional high explosive). Solid p-CO explosively decomposes to CO(2) and glassy carbon, and thus might be used as an advanced energetic material.

A method is described for obtaining ultrahigh time-resolution vibrational spectra of shocked polycrystalline materials. A microfabricated shock target array assembly is used, consisting of a polymer shock generation layer, a polymer buffer layer, and a thin sample layer. A near-IR pump pulse launches the shock. A pair of delayed visible probe pulses generate a coherent anti-Stokes Raman (CARS) spectrum of the sample. High-resolution Raman spectra of shocked crystalline anthracene are obtained. From the Raman shock shift, the shock pressure is determined to be 2.6 GPa. The rise time of shock loading is 400 ps. This rise time is limited by hydrodynamics of the shock generation layer. The shock velocity in the buffer layer is found to be 3.7 (±0.5) km/s, consistent with the observed shock pressure. As the shock propagates through a few μm of buffer material, the rise time and pressure can be monitored. The rise time decreases from ∼800 to ∼400 ps over the first 6 μm of travel, and the pressure begins to decline after about 12 μm of travel. The high-resolution CARS method permits detailed analysis of the vibrational line shape. Simulations of the CARS spectra show that when the shock front is in the crystal layer the spectral linewidths are inhomogeneously broadened by the distribution of pressures in the layers. When the crystal layer is behind the front, the spectral linewidth can be used to estimate the temperature. The increase of the spectral width from the ambient 4 to ∼6.5 cm−1 is consistent with the expected temperature increase of ∼200°.

Angle-resolved x-ray diffraction patterns of Xe to 127 GPa indicate that the fcc-to-hcp transition occurs martensitically between 3 and 70 GPa in diamond-anvil cells without an intermediate phase. These data also reveal that the transition occurs by the introduction of stacking disorder in the fcc lattice at low pressure, which grows into hcp domains with increasing pressure. The small energy difference between the hcp and the fcc structures may allow the two phases to coexist over a wide pressure range. Evidence of similar stacking disorder and incipient growth of an hcp phase are also observed in solid Kr.

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Vanadium has been reported to undergo phase transition upon compression from bcc to rhombohedral structure around 62 GPa. In this paper we confirm the bcc to rhombohedral phase transition at 61.5 GPa under quasi hydrostatic compression in Ne pressure medium. Under nonhydrostatic condition we find the phase transition occurring at 30 GPa at ambient temperature, and 37 GPa at 425 K. We find the transition under hydrostatic condition is hindered and it can occur at much lower pressure under non-hydrostatic condition.