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

Recently, hydrogen sulfide (H2S) and phosphine (PH3) 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 H2S–PH3–H2 ternary hydrides with varying H2S and PH3 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 PH3 can be confirmed in H2S–PH3–H2 by Raman and infrared spectra, and the polymerization product, P4H6, can be recovered to ambient pressure; additionally, the polymerization pressure of PH3 is evidently hampered with increasing H2S concentration. Furthermore, it has been found that low temperatures can significantly inhibit the pressure-induced polymerization of PH3. The formation of Hittorf's phosphorus is experimentally confirmed upon unloading pressure from 100 GPa to ambient pressure, which strongly implies the decomposition of P4H6 under high pressure. The H2S–PH3–H2 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 H2S–PH3–H2 caused by dehydrogenated polymerization of P4H6 to Hittorf's phosphorus.