Structural phase transition of Cu 3N under high pressure

Abstract

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) 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 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 1/3 N ions.