Richard Briggs

High pressure polymorphism of beta-TaON

The high pressure behavior of TaON was studied using a combination of Raman scattering, synchrotron X-ray diffraction, and X-ray absorption spectroscopy in diamond anvil cells to 70 GPa at ambient temperature. A Birch-Murnaghan equation of state fit for baddeleyite structured β-TaON indicates a high bulk modulus value Ko = 328 ± 4 GPa with K = 4.3. EXAFS analysis of the high pressure XAS data provides additional information on changes in the Ta-(O,N) and Ta-Ta distances. Changes in the X-ray diffraction patterns and Raman spectra indicate onset of a pressure induced phase transition near 33 GPa. Our analysis indicates that the new phase has an orthorhombic cotunnite-type structure but that the phase transition may not be complete even by 70 GPa. Similar sluggish transformation kinetics are observed for the isostructural ZrO2 phase. Analysis of compressibility data for the new cotunnite-type TaON phase indicate a very high bulk modulus Ko ∼ 370 GPa, close to the theoretically predicted value.

Melting of Sn to 1 Mbar

The melting point of Sn was determined between 20-105 GPa using laser-heated diamond anvil cell experiments, coupled with in situ synchrotron X-ray diffraction studies. In agreement with previous LH-DAC speckle experiments, we observe a flattening of the melting slope between P = 40–60 GPa. However, we also observe that this plateau is followed by a further increase in the melting slope above P ~ 70 GPa, leading to a remarkably high melting point of Tm = 5500 K by P = 105 GPa.

Phase transitions in shock compressed bismuth identified using single photon energy dispersive X-ray diffraction (SPEDX)

We present evidence for phase transitions in shock-compressed bismuth using the SPEDX x-ray diffraction technique. Experiments were performed on the Vulcan laser at the Central Laser Facility, RAL, Didcot, UK. We observed diffraction from the (110) bcc peak of Bi-V, and from its calculated lattice parameter the pressure was determined to be approximately 17 GPa. Upon further compression (higher laser intensities), no further diffraction from solid phases was observed. Shock melting of bismuth is thought to occur between 18 and 27 GPa. Diffraction results at lower pressures as a function of delay time are also presented.

Dynamic X-Ray and Neutron Scattering: From Materials Synthesis and In-Situ Studies to Biology at High Pressure

X-ray and neutron scattering techniques are applied to a very wide range of condensed matter systems and problems ranging from solid state materials to biological organisms in order to study and understand their structures and phase transformations under static and dynamic compression, as well as their synthesis and function under extreme conditions. Here we illustrate the applications of several of these techniques to problems of current scientific and technological interest.