New Insights into the Crystal Structures of Plutonium Hydrides from First-Principles Calculations

One of the important research contents on hydrogen corrosion of plutonium is the determination of the complex crystal structures of plutonium hydrides and the bonding interactions between plutonium and hydrogen. However, it is very difficult to carry out the structural characterization of plutonium hydrides because of their high activity, high toxicity, and radioactivity. In this work, the crystal structures, lattice vibrations, and bonding properties of plutonium hydrides under ambient pressure are investigated by means of the density functional theory + <i>U</i> approach. Results show that PuH₃ exhibits many competition phase structures. After considering spin polarization, strong correlation (<i>U</i>), and spin–orbit coupling effects on the total energy and lattice dynamics stability, it is found that PuH₃ at ambient pressure is more likely to be hexagonal <i>P</i>6₃<i>cm</i> or trigonal <i>P</i>3<i>c</i>1 structure, instead of the usual supposed structures of hexagonal <i>P</i>6₃/<i>mmc</i> (LaF₃-type) and face-centered cubic (BiF₃-type). The calculated electronic structures clearly indicate that <i>P</i>6₃<i>cm</i> (<i>P</i>3<i>c</i>1) PuH₃ is a semiconductor with a small band gap about 0.87 eV (0.85 eV). The Pu–H bonds in Pu hydrides are dominated by the ionic interactions