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. 2019 May 8;9:7108. doi: 10.1038/s41598-019-43601-z

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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The experimental pressure and temperature conditions and observed phase(s) of FeH_x in this study. (a) The solid circles and open squares represent the experimental conditions of Rietveld refinement for fcc FeH_x and phase observation, respectively. The yellow and blue arrows indicate the heating and cooling paths, respectively. (b) The observed phase(s) in all experimental conditions. The uncertainties in temperature are estimated to be ±50 K. The overall uncertainties in pressure are estimated to be <0.5 GPa; this includes the differences in pressure of 0.2–0.3 GPa before and after neutron diffraction measurement and experimental errors of ~0.1 GPa. Colored symbols show the observed phase(s). Gray star: bcc + dhcp + fcc, blue solid diamonds: bcc, magenta open diamonds: bcc + fcc, red solid squares/triangles: fcc (in heating/cooling paths, respectively), yellow open squares/triangles: fcc + dhcp (in heating/cooling paths, respectively), green solid circles: dhcp/hcp, light blue open circles: dhcp/hcp + bcc. The hcp phase was observed under low temperature conditions where no hydrogen was released from the hydrogen source, NH₃BH₃. The magenta bold line represents the phase boundary of FeH_x phases obtained in this study. The green dotted line and the blue dashed line represent the phase boundaries of FeH_x and Fe as reproduced from previous studies, respectively^15,16,26.