Experimental phase transition mapping for hydrogen above 300 K up to 300 GPa
A vast amount of Raman spectroscopic data, obtained using diamond anvil cell technique under in situ high pressure-temperature conditions, has been used for mapping the phase transitions of hydrogen in the temperature range of 300 K to 900 K and pressure up to 300 gigapascal, a pressure-temperature region in which most phase information was unknown previously. The isothermal and isobaric dependencies in frequency and peak width for intramolecular vibration Raman mode of hydrogen are established based on thousands of data files which are measured during hundreds of independent high pressure-temperature experimental runs. Discontinuities of pressure and temperature dependencies in frequency and peak-width, together with appearance or disappearance of observed Raman modes were obtained. Those transition data show self-consistency and have been used for outlining 13 phase transition boundaries and 15 possible phases. This large, diversified behavior of spectra demonstrates that surprisingly rich and complicated phase transitions may exist in this pressure-temperature region.