Single-crystal structure analysis of KNbO3 has been executed under high pressure through diamond anvil cell installed in the four-circle diffractometer using synchrotron radiation at Photon Factory, KEK in order to clarify the dielectric property. KNbO3 has three structural transitions with increasing pressure at ambient temperature: from orthorhombic structure with the space group Cm2m (Amm2) to tetragonal structure (P4mm) at about 7.0 GPa, to cubic structure (Pm3m) at about 10.0 GPa. The highest-pressure cubic phase is paraelectric, and the other two phases are ferroelectric. The dielectric changes in KNbO3 are clarified by the successive pressure-change of the electron density distribution observed by maximum entropy method (MEM) using high-pressure diffraction data. The MEM electron density maps suggest that the tetragonal phase designates the largest polarization among three polymorphs. The maps also indicate that the localization of the valence electron around the cation position is more enhanced under higher pressure.

It has been long speculated that extreme pressures and temperatures produce unexpected chemcial phenomena. In this presentation, I discussed the reaction kinetics obtained from a tight binding MD simulation of PETN decomposition

For A723 steel large caliber gun barrel applications, high pressure (∼700MPa), rapid cyclic heating-cooling (∼1250°C), and aggressive propellant gases (CO, CO2, H2O, H2, N2, NH3, CH4, H2S etc) operational environment can cause severe wear and erosion damages to the bore, reducing the service life of the component.Refractory bore coatings can help protect the steel bore to extend service life. Cr electroplating process is currently being widely used in industry and in the military, but toxic wastes from the process are difficult and expensive to dispose. Plasma enhanced magnetron sputtering techniques are being developed for potential replacement of the Cr electroplating process. In this work, we compared A723 steel specimens coated with electroplated Cr and plasma enhanced magnetron sputtered Ta and Cr coatings. The specimens were subjected to analytical testing, including scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, metallography; and adhesion testing, including groove test, a pulsed laser heat test to simulate cyclic thermal environment of the bore, and actual firing test. Steel samples electroplated with HC (high contraction) Cr showed extensive pre-deposition cracks, it also showed cohesive failures under groove adhesion test. When subjected to cyclic high pressure and temperature operation, gas-metal interactions led the as-deposited cracks to grow wider and new cracks to develop, allowing hot pressurized propellant gases to penetrate the cracks and erode the steel substrate. Plasma enhanced sputtered Ta and Cr coatings on steel were harder and denser compared to conventional magnetron sputtered coatings. Under groove testing, they showed no cracks, no cohesive and no adhesive failures. When subjected to cyclic pulsed laser heating simulation at 1490°K, thick sputtered Ta showed no crack, no delamination, and no failures. A heat affected zone was observed in steel, which was caused by tempered to untempered martensite conversion. Our data also showed that Ta sputtered in Ar consisted of minimum interface meta-stable tetragonal Ta fingers, which converted to bcc Ta in the heat affected zone; Ta sputtered in Kr consisted of 100% stable bcc Ta under similar experimental conditions.

We propose an explicit scheme to include the fugacity of nitrogen in computations of phase diagrams of nitride compounds at high-temperature/high-pressure conditions. The assessment is based on available thermochemical data and two kind of extrapolating functions to provide upper and lower boundary for the fugacity coefficient as a funtion of p and T. The procedure is applied to investigate the synthesis of novel nitrides of tantalum, tungsten, and platinum. The combination of first-principle and thermochemical calculations let us predict the synthesis of a new high-pressure phase of Ta3N5 at about 27 GPa. Synthesis of WN2 becomes feasible at about 45 GPa. We furthermore explain why the synthesis of the noble metal subnitride, PtN2, occurs at about 40 GPa, and why PtN is not accessible in high-pressure experiments.

Insertion of cubane (C8H8) into the octahedral voids of the C60 lattice leads to the formation of an interesting rotor-stator compound which can be converted into a C60 co-polymer by heating. We have treated a number of C60·C8H8 samples for up to 3 h each in the range 380-875 K under pressures up to 2 GPa. The resulting materials were investigated by Raman spectroscopy and X-ray diffraction. Depending on treatment conditions, at least five different structural phases can be found. In addition to the four structural phases observed at atmospheric pressure and different temperatures we find that a new polymeric state is created at pressures above 1 GPa, and we tentatively identify its structure as pseudo-orthorhombic. The cubic-orthorhombic phase transition line is found to have a slope of 295 K GPa-1, much larger than the slope of the fcc-sc line in pure C60.