We have performed a high pressure synchrotron X-ray diffraction study of the ionic salt, cesium fluoride (CsF), up to 120 GPa. We observed the B1 → B2 phase transition near 5 GPa as previously reported. Beyond this pressure, no phase transitions were determined to have occurred up to the highest pressure studied. Unit cell data were calculated from the known B2 (CsCl) structure for all of the pressures studied above 5 GPa, and an equation of state (EOS) was fit to the data using a 3rd order Birch–Murnaghan equation in this phase. Density Functional Theory (DFT) was also employed to compute an EOS for comparison purposes. Our experimental results agreed very well with both sets of the predicted EOS.

We performed two high pressure resonant X-ray emission experiments (RXES) on tungsten oxide (WO₃), and a mixture of WO₃ and ammonia borane (NH₃BH₃), respectively. In the first experiment, WO₃ (confined by a Be gasket) was pressurized and RXES spectra were collected from ambient pressure up to 54.8 GPa via incident X-ray excitation of the W L_III line at 10.207 keV and collection of emission spectra from the L_α1 line near 8.398 keV. The spectra display significant alterations, in particular, a diminishment of one of the spectral lines with pressure suggesting some electronic state changes with pressure in WO₃ which were largely reversible upon decompression of the sample to ambient pressure. For the second experiment, a powder mixture of WO₃ and NH₃BH₃ was pressurized and irradiated to release H₂. An RXES pattern was recorded at 4 GPa which displayed little difference between the RXES spectrum recorded of pure WO₃ in the first experiment. However, at 10 GPa, a dramatic change occurred in the RXES spectrum suggesting that the H₂ reacted with and/or intercalated into the WO₃ lattice. These studies suggest the possibility of harnessing useful hard X-ray photochemistry as a novel means to dope semiconductors.

We study the dynamical stability of face centered cubic lithium at 25 GPa within ab initio density functional theory calculations. The system shows an extremely softened transverse acoustic mode in the Γ–K high symmetry line, whose frequency is difficult to converge within a first-principles harmonic approach. We estimate the anharmonic correction of this value within the frozen phonon approximation assuming that the transverse acoustic mode only interacts with itself. By solving the Schrödinger equation for the potential energy curve and displacements along the vibrational mode of interest, we obtain the anharmonic eigenvalues and eigenfunctions. While the harmonic approach yields a phonon frequency of −28.6 cm⁻¹ for this mode, anharmonicity renormalizes dramatically this value up to 115.3 cm⁻¹. Thus, anharmonic effects seem to dynamically stabilize this system.

We have performed first-principles calculations of the structural stability, superconductivity, and anharmonicity of phosphorus under high pressure. The simple hexagonal (sh) structure transforms into an experimentally observed cI16 structure via a body-centered cubic (bcc) structure. In the transition from an sh into bcc structure, the superconducting critical temperature T_c increases from 0.5 to 12 K, which is the highest T_c in phosphorus. It decreases to 6 K in the transition into the cI16 phase. The pressure-dependence of T_c is related to that of the density of states at the Fermi level. In addition, we investigated anharmonicities in phosphorus under high pressure.

Numerical calculations of the optical energy gap and the optical gains g_TE, g_TM of TE and TM polarization modes in p-Al_xGa_1−xAs/GaAs_0.84P_0.16/n-Al_xGa_1−xAs laser diode structure are carried out for uniaxial compression up to P = 10 kbar along in-plane and normal to a heterostructure directions at temperature interval 77–300 K. The optical energy gap shift under compression is substantially anisotropic and does not change significantly between 77 and 300 K. The g_TM/g_TE ratio is also almost insensitive to the temperature but demonstrates several times decrease under in-plane compression and no change under compression normal to a heterostructure.

Nd_3.5Sm_0.5Ni₃O₈ is a candidate for high-T_c superconductor, due to the close structural and electrical similarities with high-T_c cuprates. In electrical resistivity measurement, Nd_3.5Sm_0.5Ni₃O₈ shows a semiconducting behavior. However, by intercalation and subsequent deintercalation treatments with sulfur, Nd_3.5Sm_0.5Ni₃O₈ displays metallic behavior down to 20–40 K, followed by the weak semiconducting tendency at lower temperatures. In this study, the electrical resistivity measurements under high pressures up to 2 GPa were performed for a semiconducting sample of Nd_3.5Sm_0.5Ni₃O₈. We discuss the electrical properties of this material, combining the high-pressure resistivity data with measurements on metallic samples at ambient pressure.

We measured the electrical resistivity ρ of CeIr(In_1−xCd_x)₅ under pressure for x = 0.05 and 0.10, which show the onset of superconductivity (SC) at T_sc^onset ~ 0.9 K and antiferromagnetic transition at T_N ~ 3.4 K. For x = 0.05, T_sc^onset increases by applying pressure up to 2.8 GPa and zero resistivity is observed at T_sc^ρ=0 above 2.4 GPa. For x = 0.10, the pressure dependence of T_N shows peak at around 2 GPa and T_N seems to be 0 K toward 3 GPa, where SC phase appears. The maximum value of T_sc^ρ=0 is independent on amount of doped Cd, showing 1.35 K. We analyzed the temperature dependence of the electrical resistivity ρ for x = 0.05 and 0.10 under pressure using the following equation, ρ = ρ₀ + ATⁿ. This analysis revealed that ρ shows the sublinear temperature dependence (n < 1) in the wide temperature region above T_sc^ρ=0, and ρ₀ decreases abruptly in the pressure region where T_sc^ρ=0 indicates a maximum.