Structural phase transition of Cu_3N under high pressure

摘要

We performed the high-pressure angle-resolved X-ray diffraction experiments on Cu_3N up to 36.0 GPa. It was found that a crystal structure phase transition begins to take place at ～5.5 GPa on Cu_3N. Under high pressure, Cu_3N transforms to a new simple tetragonal structure denoted by Cu(1)_3Cu(2)_xN_((1+x3)), because parts of Cu and N ions occupy the vacant sites in the crystal lattice. In this structure, Cu(1) and Cu(2) denote the primal Cu position and the vacant position in ReO_3 type Cu_3N, respectively. The content x is increasing with pressure, indicating that the phase transition is a gradual change. When pressure is greater than 12 GPa, x keeps 1 up to the maximum pressure, so Cu_3N completely transforms to a body-center tetragonal structure, where the N sites are filled with 13 N ions.