Phase diagram of the Eu-H system at high temperatures and high hydrogen pressures

作者：Saitoh Hiroyuki^*; Machida Akihiko; Matsuoka Takahiro; Aoki Katsutoshi

来源：Solid State Communications, 2015, 205: 24-27.

DOI：10.1016/j.ssc.2014.12.019

• Hydride
• Rare-earth metal
• High pressure
• Synchrotron radiation x-rays

The phase boundary between the hydrogen rich phases EuHx>2-III and EuHx-3-IV, determined by x-ray diffraction and infrared absorption measurements. Phase IV is characterized as a high temperature phase of phase III over an investigated pressure range of 4-10 GPa. The transition temperature exhibits a maximum value of 550 K at 7 GPa, where the slope of the boundary switches from positive to negative. The III-IV phase transition is likely accompanied by hydrogen absorption and a resulting valence change of the Eu cation: EuH2.2 (divalent) -> EuH3 (trivalent). The small volume change associated with this transition is interpreted as the volume expansion due to hydrogen absorption being compensated by volume contraction due to the Eu2+ -Eu3+ valence change. This compensation is considered to be a characteristic feature of rare-earth metals with localized f-electrons.

• 出版日期2015-3