Experimental and theoretical study of Li3N at high pressure

X rays from the Cornell High Energy Synchrotron Source were used to study t he crystal structure of Li3N over a pressure range of 0 to 35 GPa at ambien t temperature. Before loading, both the hexagonal D-6h(4) (P6(3)/mmc) and t he hexagonal D-6h(1) (P6/mmm) phases were present. At modest pressure, the D-6h(1), structure transforms completely into the D-6h(4) structure. A two- parameter Birch equation was fitted to the data to determine the equation o f state (EOS) of the D-6h(4) structure, which is compared with a theoretica l equation of state produced by our total-energy calculations in the framew ork of the local-density approximation. The experimental EOS was then used to determine the change in Gibb's free energy as a function of pressure for Li3N to 35 GPa at ambient temperature. The likelihood of a phase transitio n to a cubic structure at 35 GPa (as calculated by theory) based on observe d optical changes is discussed. [S0163-1829(99)06609-6].