Crystal Structures and Properties of Iron Hydrides at High Pressure

TL;DR

This study predicts new high-pressure iron hydride structures using evolutionary algorithms and density functional theory, revealing their stability, structures, and electronic properties at 150-300 GPa.

Contribution

It introduces previously unreported stable and metastable iron hydrides at high pressures, expanding understanding of their structures and properties.

Findings

Predicted new stable FeH5, FeH6, FeH7, and FeH8 phases.

Identified non-superconducting FeH5 phases.

Discovered a unique 1D hydrogenic lattice in FeH8.

Abstract

Evolutionary algorithms and the particle swarm optimization method have been used to predict stable and metastable high hydrides of iron between 150-300 GPa that have not been discussed in previous studies. Cmca FeH5, Pmma FeH6 and P2/c FeH6 contain hydrogenic lattices that result from slight distortions of the previously predicted I4/mmm FeH5 and Cmmm FeH6 structures. Density functional theory calculations show that neither the I4/mmm nor the Cmca symmetry FeH5 phases are superconducting. A P1 symmetry FeH7 phase, which is found to be dynamically stable at 200 and 300 GPa, adds another member to the set of predicted nonmetallic transition metal hydrides under pressure. Two metastable phases of FeH$_8$ are found, and the preferred structure at 300 GPa contains a unique 1-dimensional hydrogenic lattice.