Novel Fe hydrides and magnetism in the Fe-H system at high pressures

Abstract

The structure and properties of metal-hydrides at extreme conditions is key to the understanding of hydrogen-storage technologies, high-temperature superconductivity, and the dynamics of planetary cores. Here we investigate the phase relations and magnetic properties of iron hydrides, including two novel FeHx compounds, up to 63 GPa and 1800 K by Synchrotron Mössbauer Source spectroscopy and single-crystal X-ray diffraction. We observe the formation of a novel monoclinic iron hydride phase Fe2H∼3 at 63 GPa and 1000 K, which breaks down to a stoichiometric hexagonal closed packed FeH phase upon decompression below 52 GPa at 300 K. The long-range magnetic order in the two newly-synthetized phases persists to higher pressures compared to the well-known double hexagonal closed packed and face-centered cubic phases of FeH. The formation of magnetic Fe-H phases with high hydrogen concentration may influence the magnetic behavior of planetary metallic cores.

Electronic properties of single-crystalline Fe4O5

“…To date, band structure calculations have been inconsistent in the prediction of the electronic properties of Fe 4 O 5 , reporting it to be a metal, 49,101 a wide-gap semiconductor, 50 or to be a narrow-gap semiconductor with E g = 0.2 eV. 102 Our study resolves these discrepancies.…”

“…4b) well explains the non-zero density of states at the Fermi level. 49,101 Whereas, due to the low carrier mobility (Fig. 4c), its electrical conductivity indeed may look as semiconducting.…”

Orthogonal magnetic structures of Fe4O5: representation analysis and DFT calculations

“…Since the discovery of novel high-pressure iron oxides, their crystal chemistry and physical properties have been of great interest. 1–15 Based on the common packing motif, these compounds constitute a homologous series n FeO· m Fe 2 O 3 , containing η-Fe 2 O 3 , HP-Fe 3 O 4 , Fe 4 O 5 , Fe 5 O 6 , Fe 5 O 7 , etc . 4 Their crystal structures consist of two main building blocks, namely the slabs of edge-shared Fe–O octahedra separated by arrays of one-dimensional (1D) chains of Fe ions coordinated by a trigonal prism (see Fig.…”

“…Recently, a unified approach to this series based on a specific crystallographic generation mechanism has been proposed, which naturally classifies these oxides in terms of a sequence of the slabs or, in other words, a slab cycle. 13 Depending on the type of the slab cycle, this series can be divided into two groups, an orthorhombic N -family and a monoclinic N , N + 1 family. The former is built by only one slab of N octahedra width, exemplified by η-Fe 2 O 3 , HP-Fe 3 O 4 , Fe 4 O 5 , and Fe 5 O 6 with N = 1, 2, 3, and 4, respectively.…”

“…For the N -family in the charge-averaged state, a generic magnetic structure was proposed where the collinear slab and chain subsystems are orthogonal to each other. 13 The resulting magnetic structure will be either ferromagnetic or antiferromagnetic depending on whether N is odd or even, respectively. The remarkable feature here is that the 1D chains are symmetry protected from the magnetic perturbation of the surrounding slabs and order magnetically at much lower temperatures relative to the slabs, about 100 K versus 300 K. 13 These features, together with the fact that ab initio calculations show a strong dependence of the anisotropic conductivity on the magnetic state, 13 show the great potential of these compounds to host various magnetotransport phenomena and even to realize theoretical models of coupled 1D wires.…”