Dehydrogenation through pressure induced polymerization processes of PH3*

PH₃ is studied to understand the superconducting transition and responsible stoichiometry under high pressure by means of Raman, IR, and x-ray diffraction measurements, and theoretical calculations. It is found PH₃ is stable up to about 8 GPa and then starts to dehydrogenate through two dimerization processes at room temperature as pressure up to 25 GPa. Two resulting phosphorus hydrides, P₂H₄ and P₄H₆, are verified experimentally and can be recovered to ambient pressure. On further compression above 35 GPa, P₄H₆ directly decomposes into elemental phosphorus. The superconductivity transition temperatures of P₄H₆ at 100 and 200 GPa have been predicted to be 13 and 67 K in agreement with reported results, suggesting it might responsible for the superconductivity at higher pressures. Our results clearly show that P₂H₄ and P₄H₆ are only stable P-H compounds between PH₃ and elemental phosphorus, shedding light on the superconducting mechanism.