An improved calibration curve of the pressure shift of the ruby R1 emission line was obtained under quasi‐hydrostatic conditions in the diamond‐window, high‐pressure cell to 800 kbar. Argon was the pressure‐transmitting medium. Metallic copper, as a standard, was studied in situ by X ray diffraction. The reference pressure was determined by calibration against known equations of state of the copper sample and by previously obtained data on silver.

High-pressure Raman, infrared, x-ray, and neutron studies show that H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2O molar ratio of 1:2. The clathrate cages are multiply occupied, with a cluster of two H2 molecules in the small cage and four in the large cage. Substantial softening and splitting of hydrogen vibrons indicate increased intermolecular interactions. The quenched clathrate is stable up to 145 kelvin at ambient pressure. Retention of hydrogen at such high temperatures could help its condensation in planetary nebulae and may play a key role in the evolution of icy bodies.

The wavelength shift with pressure of the ruby R1 fluorescence line (Δλ) has been calibrated in the diamond-window pressure cell from 0.06 to 1 Mbar. This was done by simultaneously making specific volume measurements of four metals (Cu, Mo, Ag, and Pd) and referring these results to isothermal equations of state derived from shock-wave experiments. The result is P (Mbar) = (19.04/5) {[(λ0+Δλ)/λ0]5−1}, where λ0 is the wavelength measured at 1 bar.

A piezoelectric material is one that generates a voltage in response to a mechanical strain (and vice versa). The most useful piezoelectric materials display a transition region in their composition phase diagrams, known as a morphotropic phase boundary, where the crystal structure changes abruptly and the electromechanical properties are maximal. As a result, modern piezoelectric materials for technological applications are usually complex, engineered, solid solutions, which complicates their manufacture as well as introducing complexity in the study of the microscopic origins of their properties. Here we show that even a pure compound, in this case lead titanate, can display a morphotropic phase boundary under pressure. The results are consistent with first-principles theoretical predictions, but show a richer phase diagram than anticipated; moreover, the predicted electromechanical coupling at the transition is larger than any known. Our results show that the high electromechanical coupling in solid solutions with lead titanate is due to tuning of the high-pressure morphotropic phase boundary in pure lead titanate to ambient pressure. We also find that complex microstructures or compositions are not necessary to obtain strong piezoelectricity. This opens the door to the possible discovery of high-performance, pure-compound electromechanical materials, which could greatly decrease costs and expand the utility of piezoelectric materials.

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We report the results of X ray diffraction experiments with the diamond anvil cell to pressures above 300 GPa at room temperature on pure iron and an iron‐nickel alloy. These data extend throughout the pressure range of the bulk of the outer core of the Earth and provide for the first time direct pressure‐volume measurements on geophysically important materials at such conditions. Both iron and iron‐nickel are observed to remain in the hexagonal close‐packed structure to the maximum pressures. A combined fit to all recent compression data up to 300 GPa gives the following Birch‐Murnaghan equation‐of‐state (EOS) parameters for iron: V02 = 6.73(1) cm3 mol−1, K02 = 165(4) GPa, and K′02 = 5.33(9). (Value in parentheses refers to the uncertainty of the last digit; e.g., 6.73(1) refers to 6.73+0.01.). Similar parameters are obtained with a recent “universal” form of the EOS of solids. For an Fe0.8 Ni0.2 alloy, the equation‐of‐state parameters are nearly identical, within error: V02 = 6.737(5) cm3 mol−1, K02 = 172(2) GPa, and K′02 = 4.95(9). In terms of volume, the alloy equation‐of‐state is indistinguishable from that of pure iron and the densities differ (dominantly in proportion to their atomic weights) by ∼0.3 Mg m−3 at 330 GPa. Within the range of uncertainty in Earth model densities and trade‐offs with the percentage light component in the core, nickel could be present in the core in an amount at least equal to its estimated abundance in the Earth. A direct comparison with (solid) inner core densities is now possible and places direct constraints on the thermal models of the Earth's interior.

There has been considerable interest in the synthesis of new nitrides because of their technological and fundamental importance. Although numerous metals react with nitrogen there are no known binary nitrides of the noble metals. We report the discovery and characterization of platinum nitride (PtN), the first binary nitride of the noble metals group. This compound can be formed above 45-50 GPa and temperatures exceeding 2,000 K, and is stable after quenching to room pressure and temperature. It is characterized by a very high Raman-scattering cross-section with easily observed second- and third-order Raman bands. Synchrotron X-ray diffraction shows that the new phase is cubic with a remarkably high bulk modulus of 372(+/-5) GPa.