We report a novel phase of carbon possessing a monoclinic C2/m structure (8 atoms/cell) identified using an ab initio evolutionary structural search. This polymorph, which we call M-carbon, is related to the (2x1) reconstruction of the (111) surface of diamond and can also be viewed as a distorted (through sliding and buckling of the sheets) form of graphite. It is stable over cold-compressed graphite above 13.4 GPa. The simulated x-ray diffraction pattern and near K-edge spectroscopy are in satisfactory agreement with the experimental data [W. L. Mao, Science 302, 425 (2003)10.1126/science.1089713] on overcompressed graphite. The hardness and bulk modulus of this new carbon polymorph are calculated to be 83.1 and 431.2 GPa, respectively, which are comparable to those of diamond.

High-pressure structures of germane (GeH4) are explored through ab initio evolutionary methodology to reveal a metallic monoclinic structure of C2/c (4 molecules/cell). The C2/c structure consists of layerlike motifs containing novel "H2" units. Enthalpy calculations suggest a remarkably wide decomposition (Ge+H2) pressure range of 0-196 GPa, above which C2/c structure is stable. Perturbative linear-response calculations for C2/c GeH4 at 220 GPa predict a large electron-phonon coupling parameter lambda of 1.12 and the resulting superconducting critical temperature reaches 64 K.

Thin, rectangular C60 nanorods in face‐centered cubic structure are synthesized by using m‐xylene as a shape controller. These unusual nanorods (see figure) can easily grow on various substrates. The smallest nanorods have widths smaller than 30 nm. The nanorods are highly crystalline in single phase. A significant expansion of the lattice constant is also found in the C60 nanorods when their widths decrease below about 80 nm.

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There is great interest in the exploration of hydrogen-rich compounds upon strong compression where they can become superconductors. Stannane (SnH 4 ) has been proposed to be a potential high-temperature superconductor under pressure, but its high-pressure crystal structures, fundamental for the understanding of superconductivity, remain unsolved. Using an ab initio evolutionary algorithm for crystal structure prediction, we propose the existence of two unique high-pressure metallic phases having space groups Ama2 and P6 3 ∕mmc, which both contain hexagonal layers of Sn atoms and semimolecular (perhydride) H 2 units. Enthalpy calculations reveal that the Ama2 and P6 3 ∕mmc structures are stable at 96-180 GPa and above 180 GPa, respectively, while below 96 GPa SnH 4 is unstable with respect to elemental decomposition. The application of the Allen-Dynes modified McMillan equation reveals high superconducting temperatures of 15-22 K for the Ama2 phase at 120 GPa and 52-62 K for the P6 3 ∕mmc phase at 200 GPa.hydrogen-rich compounds | metallization | electron-phonon coupling R elatively high-temperature superconductivity is now documented in light-element metals such as Li under pressure (1-3) and MgB 2 (4), where transition temperatures T c up to 20 K and 39 K, respectively, are observed. There is great interest in exploration of unique superconducting phases in other lightelement materials because their high phonon frequencies can enhance electron-phonon coupling (see ref. 5). As the lightest element, hydrogen at very high densities is also predicted to be a superconductor with high transition temperatures (6-8). Experiments indicate that the predicted metallic and superconducting states of hydrogen remain above ∼300 GPa (9-11). It has been proposed that hydrogen-rich compounds (e.g., group IVa hydrides (12)) are expected to metallize at pressures considerably lower than pure hydrogen due to the chemical "precompression" caused by heavier elements; these metallization pressures may fall within the range of current capabilities of static compression techniques. The exploration of potential superconductivity in these hydrogen-rich compounds (e.g., SiH 4 , GeH 4 , and SnH 4 ) is thus desirable and numerous studies have been performed (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Strikingly, recent experiments (15,18) show that SiH 4 transforms to a metallic phase near 50-60 GPa with a superconducting T c of 17 K at 96 and 120 GPa, though debate remains (26). We have recently predicted (17) that GeH 4 becomes a high-temperature superconductor with a T c of 64 K at 220 GPa. A theoretical study of SnH 4 (21) predicts that its T c can be even higher, reaching the value of 80 K. Using simulated annealing and geometry optimization, that study found that the high-pressure phase of SnH 4 has P6∕mmm symmetry with a layered structure intercalated by molecular H 2 units, wherein the nearest H-H distance, 0.84 Å, is short enough to be considered as covalent bonding, but significantly longer than the 0.74 Å in the free H ...

First-principles calculations were performed on the superhard material, WB4 (Vicker hardness exceeding 46GPa), to reveal the origin of its high hardness. Our simulated lattice parameters, bulk modulus, and hardness are in excellent agreement with the experimental data. A three-dimensional B network with a peculiar B2 dimer along the z-axis and a xy planar honeycomb B sublattice is uncovered to be mainly responsible for the high hardness. We further predicted that five other transition metal B compounds (TMB4, TM=Re, Mo, Ta, Os, and Tc) within the WB4 structure are potential superhard materials.

Single-crystalline C 60 ‚1m-xylene nanorods with a hexagonal structure were successfully synthesized by evaporating a C 60 solution in m-xylene at room temperature. The ratio of the length to the diameter of the nanorods can be controlled in the range of ≈10 to over 1000 for different applications. The photoluminescence (PL) intensity of the nanorods is about 2 orders of magnitude higher than that for pristine C 60 crystals in air. Both UV and Raman results indicate that there is no charge transfer between C 60 and m-xylene. It was found that the interaction between C 60 and m-xylene molecules is of the van der Waals type. This interaction reduces the icosahedral symmetry of C 60 molecule and induces strong PL from the solvate nanorods.

In this paper, CeO 2 nanocubes with the (200)terminated surface/graphene sheet composites have been prepared successfully by a simple hydrothermal method. It is found that the CeO 2 nanocubes with high crystallinity and specific exposed surface are well dispersed on well-exfoliated graphene surface. The (200)-terminated surface/graphene sheet composites modified electrode showed much higher sensitivity and excellent selectivity in its catalytic performance compared to a CeO 2 nanoparticle-modified electrode. The photoluminescence intensity of the CeO 2 anchored on graphene is about 30 times higher than that of pristine CeO 2 crystals in air. The higher oxygen vacancy concentration in CeO 2 is supposed to be an important cause for the higher photoluminescence and better electrochemical catalytic performance observed in the (200)-terminated surface/graphene sheet composites. Such ingenious design of supported well-dispersed catalysts in nanostructured ceria catalysts, synthesized in one step with an exposed high-activity surface, is important for technical applications and theoretical investigations.