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The ν1-ν18a Fermi resonance (FR) of phenol were investigated by pressure-dependent Raman spectroscopy from atmospheric up to P=15.2GPa and temperature-dependent Raman spectroscopy from 40 down to T=-180°C, respectively. In the case of pressure, we found the Fermi coupling coefficient W, which were calculated based on the FR theory, exposed a value turnover between 1.912 and 2.244GPa in the process of increasing the pressure. This turnover phenomenon of the Fermi coupling coefficient W has been ascribed to the crystal structure of phenol evolving towards a more symmetric structure with pressure, from a structure like a pseudo-threefold helical chain at ambient pressure to like a ribbon arrangement at 1.912GPa, then to adopt a herringbone arrangement at much higher pressure. On the other hand, we also found the Fermi coupling coefficient W exhibited monotonic reduction without turnover points appearing by decreasing the temperature. The tendencies of the Fermi coupling coefficient W with temperature were in good agreement with the pressure dependence of the Fermi coupling coefficient W in the region of ambient to 1.912GPa, indicating that the effect of pressure and temperature on the FR of phenol in this region might be the same. A conformation evolving induced by pressure and temperature on the ν1 and ν18a FR of phenol have been analyzed.

With the increasing demand for specific applications in high pressure and electronic devices, the search for superhard superconducting materials remains a topic of great interest. Using particle swarm optimization algorithm, we report five competitive structures with clear tetrahedrally sp(3) hybridization, among which two metallic orthorhombic structures (Pmm2 and Pmma) with the maximal stable bonds (C-C + B-N) are energetically more favorable than earlier proposed structures. Further first principles calculations suggest that the predicted five structures possess simultaneously superhard and superconducting properties. The five structures are with the similar calculated hardness (56-58 GPa), but show distinct difference in superconducting critical temperature, ranging from 2 to 53 K (with the Coulomb parameter mu* of 0.13). (C) 2011 Elsevier Ltd. All rights reserved.

Using ab initio crystal structure prediction, we have predicted several polytypic structures for B 2 O under high pressure. The structural parameters, total energies, electronic properties and hardness of the obtained structures have been studied using pseudopotential density functional theory within the local density approximation. We find that a monoclinic C 2 /m phase is the most energetically favorable structure; however, its X-ray diffraction pattern could not fit into the experimental data [J. Mater. Sci. Lett. 6 (1987) 683]. Instead, X-ray diffraction patterns of the energetically less stable tetragonal P 4 2 mc and designed P -4 m 2 structures are in overall agreement with the experimental data. The simulated hardness of P 4 2 mc and P -4 m 2 are 40.5 and 44.8 GPa, respectively, in accordance with the experimental values of 33.5 ~ 40.5 GPa.