Experimental phase transition mapping for hydrogen above 300 K up to 300 GPa

Abstract

We report a phase diagram mapping for solid hydrogen based on several thousands of Raman spectroscopic data points obtained at simultaneous high-pressure and -temperature (PT) experiments. Information about phase behavior in the range of 300 K up to the melting line and 0-300 GPa for hydrogen has remained almost unknown to date; therefore, revealing it is very desirable. A network analysis of the isothermal and isobaric dependencies for various Raman modes has been used; discontinuities in these dependencies, plus the mode appearance/disappearance provide evidence for phase transitions. These transition data show self-consistency and have been used to outline possible phase boundaries for hydrogen in this PT region. Evidence we found shows hydrogen may experience a gradual molecular dissociation process before its metallization.