Iron-Nickel Phosphides at High Pressures and Temperatures

The phosphide minerals schreibersite (Fe,Ni)₃P, barringerite (Fe-Ni)₂P, and rhabdite (Fe,Ni)P are found in many iron-nickel meteorites and enstatite chondrites. Many iron meteorites were affected by high pressure impact metamorphism. Also it has been suggested that phosphorous may be one of the light elements in the Earth's core. It is therefore important to assess the behavior of iron-nickel-phosphides at high pressures and temperatures and determine the stability and crystal structures of any high-pressure phases. Iron and nickel phosphides have been synthesized with grain sizes up to about 50 microns and are being studied using both energy- dispersive synchrotron radiation at beamline X-17C, NSLS, Brookhaven National Laboratory and angle-dispersive synchrotron radiation at beamlines 13BM-D and 13ID-D, GSECARS, Argonne National Laboratory. Pressures ranged to 70 GPa and temperatures to about 2000 degrees C. The ambient-pressure structures of Fe₂P and Ni₂P have been determined to be P-62m and P321 with lattice parameters of a= 5.8748, c= 3.4602, and a= 5.7525, c= 3.3268 angstroms, respectively. Phase changes in both Fe₂P and Ni₂P were observed, and Equations of State are being calculated.