Unravelling decomposition products of phosphine under high pressure

Recently, the superconductivity in phosphine (PH3) has been discovered with the superconducting transition temperature T-c up to 203GPa by using high pressure resistance measurements. However, the structural information of PH3 under high pressure remains elusive. Motivated by this, in this work, the behavior of PH3 under high pressure has been investigated by Raman spectroscopy at 298K. The Raman spectra varied with pressure increasing, accompanying with the change of the sample color, which first became yellow, then red, and finally opaque. In the pressure range of 8.53-18.36GPa, the decomposition of PH3 was observed, and the main decomposition products were P2H4 and element hydrogen (H-2). Upon compression to higher pressure, the Raman signal of hydrogen vibration was observed to become stronger, indicating that PH3 or P2H4 further decomposed into element phosphorus and hydrogen. The original PH3 did not form again upon decomposition to ambient pressure. P2H4 and other decomposition products of compressed phosphine were considered as main products of the high temperature superconducting phase reported in experiment.