We have obtained bulk samples of the graphite intercalation compound, CaC6, by a novel method of synthesis from highly oriented pyrolytic graphite. The crystal structure has been completely determined showing that it is the only member of the MC6, metal-graphite compounds that has rhombohedral symmetry. We have clearly shown the occurrence of superconductivity in the bulk sample at 11.5 K, using magnetization measurements.

We measure phonon dispersion and linewidth in a single crystal of MgB2 along the Gamma-A, Gamma-M, and A-L directions using inelastic x-ray scattering. We use density functional theory to compute the effect of both electron-phonon coupling and anharmonicity on the linewidth, obtaining excellent agreement with experiment. Anomalous broadening of the E(2g) phonon mode is found all along Gamma-A. The dominant contribution to the linewidth is always the electron-phonon coupling.

Although the stability of Au in the face-centered cubic (FCC) phase at high temperatures and pressures has been well studied, the stability in other lattice phases rarely encountered in crystallite domains in microscopy studies has not been explored much because of their nanometric extensions. A recent report on Au microcrystallites crystallized in body-centered tetragonal (BCT) and body-centered orthorhombic (BCO) phases prompted the work presented here, in which we have investigated for the first time the structural stability of the BCT and BCO phases at high temperatures and separately at high pressures using high-energy synchrotron X-ray diffraction. A reversible phase transition was observed for pressures of up to ∼40 GPa, indicating unusual stability of the non-FCC Au phases. However, during a high-temperature treatment at ∼700 °C, the transformation to FCC was irreversible.