Structural phase transition of Cu3N under high pressure

We performed the high-pressure angle-resolved X-ray diffraction experiments on Cu3N up to 36.0 GPa. It was found that a crystal structure phase transition begins to take place at ∼5.5 GPa on Cu3N. Under high pressure, Cu3N transforms to a new simple tetragonal structure denoted by [Cu(1)3Cu(2)x]N(1+x/3), 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 ReO3 type Cu3N, 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 Cu3N completely transforms to a body-center tetragonal structure, where the N sites are filled with 1/3 N ions.