Pressure-Induced Multistep Dehydrogenated Polymerization and Metallization of H₂S–PH₃–H₂ Compound: Properties Measurement up to Megabar Pressures

Recently, hydrogen sulfide (H 2 S) and phosphine (PH 3 ) have attracted great attention since the observation of superconducting transitions with high crucial temperatures under high pressure, which inspired subsequent investigations of the superconductivity of nonmetallic hydrides. Here, we report the successful photochemical and thermal syntheses of a series of novel H 2 S–PH 3 –H 2 ternary hydrides with varying H 2 S and PH 3 molar ratios. Raman, infrared, UV–visible absorption spectra, and electrical transport measurements are employed to investigate the chemical reaction and electronic structure transformation under high pressure. The pressure-induced polymerization of PH 3 can be confirmed in H 2 S–PH 3 –H 2 by Raman and infrared spectra, and the polymerization product, P 4 H 6, can be recovered to ambient pressure; additionally, the polymerization pressure of PH 3 is evidently hampered with increasing H 2 S concentration. Furthermore, it has been found that low temperatures can significantly inhibit the pressure-induced polymerization of PH 3 . The formation of Hittorf’s phosphorus is experimentally confirmed upon unloading pressure from 100 GPa to ambient pressure, which strongly implies the decomposition of P 4 H 6 under high pressure. The H 2 S–PH 3 –H 2 molecule gradually turns red and is eventually opaque following compression, which is consistent with the red shift of the UV–visible absorption spectra. Furthermore, synchrotron infrared absorption spectra and electrical transport examined above 65 GPa indicate the insulator-to-metal transition of H 2 S–PH 3 –H 2 caused by dehydrogenated polymerization of P 4 H 6 to Hittorf’s phosphorus.