Almost 80 years ago it was predicted that, under sufficient compression, the H–H bond in molecular hydrogen (H2) would break, forming a new, atomic, metallic, solid state of hydrogen1. Reaching this predicted state experimentally has been one of the principal goals in high-pressure research for the past 30 years. Here, using in situ high-pressure Raman spectroscopy, we present evidence that at pressures greater than 325 gigapascals at 300 kelvin, H2 and hydrogen deuteride (HD) transform to a new phase—phase V. This new phase of hydrogen is characterized by substantial weakening of the vibrational Raman activity, a change in pressure dependence of the fundamental vibrational frequency and partial loss of the low-frequency excitations. We map out the domain in pressure–temperature space of the suggested phase V in H2 and HD up to 388 gigapascals at 300 kelvin, and up to 465 kelvin at 350 gigapascals; we do not observe phase V in deuterium (D2). However, we show that the transformation to phase IV′ in D2 occurs above 310 gigapascals and 300 kelvin. These values represent the largest known isotropic shift in pressure, and hence the largest possible pressure difference between the H2 and D2 phases, which implies that the appearance of phase V of D2 must occur at a pressure of above 380 gigapascals. These experimental data provide a glimpse of the physical properties of dense hydrogen above 325 gigapascals and constrain the pressure and temperature conditions at which the new phase exists. We speculate that phase V may be the precursor to the non-molecular (atomic and metallic) state of hydrogen that was predicted 80 years ago.
This is a preview of subscription content
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Wigner, E. & Huntington, H. B. On the possibility of a metallic modification of hydrogen. J. Chem. Phys. 3, 764–770 (1935)
van Kranendonk, J. Solid Hydrogen (Plenum Press, 1983)
Housecroft, C. E. & Sharpe, A. G. Inorganic Chemistry (Prentice Hall, 2007)
Langmuir, I. & Mackay, G. M. J. The dissociation of hydrogen into atoms. Part I. Experimental. J. Am. Chem. Soc. 36, 1708–1722 (1914)
Langmuir, I. The dissociation of hydrogen into atoms. [Part II.] Calculation of the degree of dissociation and the heat of formation. J. Am. Chem. Soc. 37, 417–458 (1915)
Goncharov, A. F., Gregoryanz, E., Hemley, R. J. & Mao, H.-k. Spectroscopic studies of the vibrational and electronic properties of solid hydrogen to 285 GPa. Proc. Natl Acad. Sci. USA 98, 14234–14237 (2001)
Loubeyre, P., Occelli, F. & LeToullec, R. Optical studies of solid hydrogen to 320 GPa and evidence for black hydrogen. Nature 416, 613–617 (2002)
Gregoryanz, E., Goncharov, A., Matsuishi, K., Mao, H.-k. & Hemley, R. Raman spectroscopy of hot dense hydrogen. Phys. Rev. Lett. 90, 175701 (2003)
Eremets, M. I. & Trojan, I. A. Evidence of maximum in the melting curve of hydrogen at megabar pressures. JETP Lett. 89, 174–179 (2009)
Subramanian, N., Goncharov, A. F., Struzhkin, V. V., Somayazulu, M. & Hemley, R. J. Bonding changes in hot fluid hydrogen at megabar pressures. Proc. Natl Acad. Sci. USA 108, 6014–6019 (2011)
Akahama, Y. et al. Evidence from x-ray diffraction of orientational ordering in phase III of solid hydrogen at pressures up to 183 GPa. Phys. Rev. B 82, 060101 (2010)
Akahama, Y., Kawamura, H., Hirao, N., Ohishi, Y. & Takemura, K. Raman scattering and x-ray diffraction experiments for phase III of solid hydrogen. J. Phys. Conf. Ser. 215, 012056 (2010)
Zha, C.-S., Liu, Z. & Hemley, R. J. Synchrotron infrared measurements of dense hydrogen to 360 GPa. Phys. Rev. Lett. 108, 146402 (2012)
Howie, R. T., Dalladay-Simpson, P. & Gregoryanz, E. Raman spectroscopy of hot hydrogen above 200 GPa. Nature Mater. 14, 495–499 (2015)
Eremets, M. I. & Troyan, I. A. Conductive dense hydrogen. Nature Mater. 10, 927–931 (2011)
Howie, R. T., Guillaume, C. L., Scheler, T., Goncharov, A. F. & Gregoryanz, E. Mixed molecular and atomic phase of dense hydrogen. Phys. Rev. Lett. 108, 125501 (2012)
Pickard, C. J. & Needs, R. J. Structure of phase III of solid hydrogen. Nature Phys. 3, 473–476 (2007)
Howie, R. T., Scheler, T., Guillaume, C. L. & Gregoryanz, E. Proton tunneling in phase IV of hydrogen and deuterium. Phys. Rev. B 86, 214104 (2012)
Howie, R. T., Gregoryanz, E. & Goncharov, A. F. Hydrogen (deuterium) vibron frequency as a pressure comparison gauge at multi-Mbar pressures. J. Appl. Phys. 114, 073505 (2013)
Howie, R. T., Magda˘ u, I. B., Goncharov, A. F., Ackland, G. J. & Gregoryanz, E. Phonon localization by mass disorder in dense hydrogen-deuterium binary alloy. Phys. Rev. Lett. 113, 175501 (2014)
Zha, C.-s., Cohen, R. E., Mao, H.-k. & Hemley, R. J. Raman measurements of phase transitions in dense solid hydrogen and deuterium to 325 GPa. Proc. Natl Acad. Sci. USA 111, 4793–4797 (2014)
McMahon, J. M. & Ceperley, D. M. Ground-state structures of atomic metallic hydrogen. Phys. Rev. Lett. 106, 165302 (2011)
Azadi, S., Monserrat, B., Foulkes, W. M. C. & Needs, R. J. Dissociation of high-pressure solid molecular hydrogen: a quantum Monte Carlo and anharmonic vibrational study. Phys. Rev. Lett. 112, 165501 (2014)
Tamblyn, I. & Bonev, S. A. Structure and phase boundaries of compressed liquid hydrogen. Phys. Rev. Lett. 104, 065702 (2010)
Morales, M., Pierleoni, C., Schwegler, E. & Ceperley, D. M. Evidence for a first-order liquid-liquid transition in high-pressure hydrogen from ab initio simulations. Proc. Natl Acad. Sci. USA 107, 12799–12803 (2010)
Knudson, M. D. et al. Direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium. Science 348, 1455–1460 (2015)
Akahama, Y. & Kawamura, H. High-pressure Raman spectroscopy of diamond anvils to 250 GPa: method for pressure determination in the multimegabar pressure range. J. Appl. Phys. 96, 3748–3751 (2004)
Akahama, Y. & Kawamura, H. Pressure calibration of diamond anvil Raman gauge to 310 GPa. J. Appl. Phys. 100, 043516 (2006)
Akahama, Y. & Kawamura, H. Pressure calibration of diamond anvil Raman gauge to 410 GPa. J. Phys. Conf. Ser. 215, 012195 (2010)
We are grateful to M. Frost for assistance during experiments. This work is supported by a Leadership Fellowship from the UK Engineering and Physical Sciences Research Council (EPSRC), reference number EP/J003999/1. P.D-S. acknowledges studentship funding from EPSRC grant number EP/G03673X/1.
The authors declare no competing financial interests.
Extended data figures and tables
a, A typical example of a spectrum from the first-order Raman band of diamond when probing the sample (orange). The frequency edge is given by the vertical dashed line at 1,796 rel. cm−1, which corresponds to a pressure of 275 GPa (ref. 27). This stressed edge is defined as the frequency that minimizes (purple). b, H2 vibrational-mode (vibron) frequency (ν1) plotted as a function of the stressed-diamond-edge frequency.
a, Vibration-mode (vibron) frequency plotted using the three pressure gauges of the stressed-diamond frequency proposed by Akahama et al.: blue squares27, green circles28 and red triangles11. b, The three pressure gauges plotted as a function of pressure, coloured as in a; the dashed line marks the highest frequency of the stressed diamond recorded on a HD sample, 1,936 rel. cm−1.
Representative Raman spectra from HD, a mixture of hydrogen (75%) and deuterium (25%), as a function of pressure at 300 K. The spectra show the evolution of the ν1 vibrational modes of HD (labelled ‘HD-ν1’) and H2 (labelled ‘H2-ν1’) from loading at 0.5–218 GPa, as labelled. Above 47 GPa, there is an observed transfer of integrated intensity from the ν1 band of H2 to the ν1 band of HD, with the latter vibrational mode becoming stronger than the former at 150 GPa, and the only resolvable ν1 band above 218 GPa. The spectra were collected using a 514-nm excitation wavelength. The spectra from this run above 218 GPa are shown in Fig. 1b.
Representative Raman spectra of the low-frequency excitations of the three isotopes (left, H2; centre, D2; right, HD) as functions of pressure during the transition from phase IV to phase IV′. The low-frequency mode L3 splits to produce mode L4.
a, Frequencies of the vibrational modes versus pressure from ref. 21 (black circles) and the current study and our previous study16 (violet squares). The open symbols represent data for H2; the symbols enclosing pluses represent data for D2. b, Representative Raman spectra of hydrogen from ref. 21 (black) and ref. 16 (violet). The dashed vertical line indicates the lowest vibrational-mode frequency (and therefore the highest pressure) observed in ref. 21.
a, Raman spectra for a pure hydrogen sample, taken using a probe laser with a wavelength of 647 nm, as function of temperature at pressures between 367 GPa and 350 GPa (black). The Raman spectrum collected 2 μm away on the rhenium gasket is shown in red. The vertical dashed lines indicate the frequency space occupied by the second-order diamond band. DE, diamond edge. b, Example spectrum of the sample (black) and the gasket (2 μm away, red), collected at 361 GPa, and the difference between them (blue).
Representative Raman spectrum demonstrating how intensities were calculated for a given spectrum. The best fit (black curve) to the experimental data (green points) is shown (measured by the left axis) along with the integrated intensities for each excitation (indicated by the height of the blue bars, measured by the right axis). The inset shows the raw value of the integrated intensities of each excitation in the main figure as a percentage of the total Raman activity. 2nd Dmd., second-order diamond band (unlabelled in the main figure).
About this article
Cite this article
Dalladay-Simpson, P., Howie, R. & Gregoryanz, E. Evidence for a new phase of dense hydrogen above 325 gigapascals. Nature 529, 63–67 (2016). https://doi.org/10.1038/nature16164
Nature Reviews Physics (2022)
Nature Physics (2021)
Applied Physics A (2021)