Sound velocities of compressed Fe₃C from simultaneous synchrotron X-ray diffraction and nuclear resonant scattering measurements

The applications of nuclear resonant scattering in laser-heated diamond anvil cells have provided an important probe for the magnetic and vibrational properties of ⁵⁷Fe-bearing materials under high pressure and high temperature. Synchrotron X-ray diffraction is one of the most powerful tools for studying phase stability and equation of state over a wide range of pressure and temperature conditions. Recently an experimental capability has been developed for simultaneous nuclear resonant scattering and X-ray diffraction measurements using synchrotron radiation. Here the application of this method to determine the sound velocities of compressed Fe₃C is shown. The X-ray diffraction measurements allow detection of microscale impurities, phase transitions and chemical reactions upon compression or heating. They also provide information on sample pressure, grain size distribution and unit cell volume. By combining the Debye velocity extracted from the nuclear resonant inelastic X-ray scattering measurements and the structure, density and elasticity data from the X-ray diffraction measurements simultaneously obtained, more accurate sound velocity data can be derived. Our results on few-crystal and powder samples indicate strong anisotropy in the sound velocities of Fe₃C under ambient conditions.