Professor Andrew Jephcoat


Visiting Professor

Email: andrew@earth.ox.ac.uk
TEL: +44 (1865) 272067
FAX: +44 (1865) 272072
Homepage: http://www.earth.ox.ac.uk/research/groups/ultra_high_pressure

Research Profile

A central feature of planetary research is the creation in the laboratory of the extreme high-pressure high-temperature states of matter. In particular, I am interested in the nature of the Earth's mantle and core and their physical and chemical interaction – processes that operate up to 3000 km below the Earth's surface. Pressures reach over 300 GPa (3 million atmospheres) with temperatures perhaps as high as 7000 K (greater than the sun surface temperature) at the center of the Earth's inner core. We achieve these conditions in the laboratory with the laser-heated diamond-anvil high-pressure cell (DAC) wherein natural or synthetic samples, fractions of a millimeter in size, are confined between two brilliant-cut, single-crystal diamond anvils. One focus of my research is a systematic improvement in the accuracy of temperature measurements and relative melting points at high-pressure in the diamond-anvil cell. For example the measurement of the melting point of iron compounds at high-pressure can be used to constrain temperatures at the Earth's Inner-Outer Core boundary.

Research at simultaneous high pressures (P) and high temperatures (T) opens many possibilities for understanding deep-Earth processes. Experimental techniques include Synchrotron X-ray diffraction and spectroscopy, Raman scattering, laser-heating, Brillouin scattering, and multi-anvil synthesis.

For example, the measurement of elastic properties of materials at pressure and temperature is fundamental because compressional and shear velocities (functions of the elastic coefficients) are primary observables in seismology.

High P and T can also change chemical bonding in materials and could lead to the synthesis of new compound structures with new and/or unusual properties. Bonding change in materials is most readily examined with vibrational spectroscopic methods (Raman and IR). Synchrotron storage rings can now offer bright, collimated sources of IR radiation orders of magnitude greater than laboratory techniques.

X-ray diffraction experiments at high-brilliance, synchrotron sources yield direct structural data on high-pressure phases and provide a measure of density and crystal structural change as a function of compression and temperature (the equation of state, EOS). Experiments have been performed at Daresbury, Brookhaven National Laboratory, Cornell and the European Synchrotron Radiation Facility, Grenoble (ESRF). I am actively involved in building the extreme conditions beamline at the new UK synchrotron X-ray source (DIAMOND).

My high-pressure research covers a wide range of material types such as planetary ices (condensed gases) and other molecular solids (e.g., C60), pure metals and their oxides, carbides, hydrides, and silicates.

Selected Publications

  • A.K. Kleppe and A.P. Jephcoat, High-pressure Raman spectroscopic studies of FeS-2 pyrite, Mineralogical Magazine, 68 (3), 433-441, 2004.
  • M.A. Bouhifd and A.P. Jephcoat, Partitioning of Ni and Co between silicate liquids and iron liquid alloy: A diamond-anvil cell study, EPSL, 209, 245-255, 2003.
  • A.K. Kleppe, A.P. Jephcoat, J.R. Smyth and D.J. Frost, On protons, and the High-Pressure Behavior of Ringwoodite, Geophysical Research Letters, 29 (21), 17-1--17-4, 2002.
  • M.D. Brasier, O.R. Green, A.P. Jephcoat, A.K. Kleppe, M.J van Kranendonk, J.F. Lindsay, A. Steele and N.V. Grassineau, Questioning the evidence for Earth's oldest fossils, Nature, 416, 76-81, 2002.
  • H. Olijnyk & A.P. Jephcoat, High-pressure vibrational studies of hcp metals by Raman spectroscopy, High Pressure Research, 22, 43-45, Sp. Iss. SI, 2002.
  • S. Merkel, A.P. Jephcoat, J. Shu, H.-K. Mao, P. Gillet and R.J. Hemley, Equation of state, elasticity, and shear strength of pyrite under high pressure, Physics and Chemistry of Minerals, 29 (1), 2002.
  • A.P. Jephcoat & K. Refson, Core beliefs, Nature N&V, 413, 27-30, 2001.
  • A.P. Jephcoat, Rare-gas solids in the Earth's deep interior, Nature, 393, 1998.
  • A.P. Jephcoat & S.P. Besedin, Temperature measurement and melting determination in the laser-heated diamond-anvil cell, Phil. Trans. Royal Soc., 354, 1996.