Oxygen-Driven Enhancement of the Electron Correlation in Hexagonal Iron at Earth’s Inner Core Conditions

Earth’s inner core (IC) consists of mainly iron with some light elements. Understanding its structure and related physical properties has been elusive as a result of its required extremely high pressure and temperature conditions. The phase of iron, elastic anisotropy, and density–velocity deficit at the IC have long been questions of great interest. Here, we find that the electron correlation effect is enhanced by oxygen and modifies several important features, including the stability of iron oxides. Oxygen atoms energetically stabilize hexagonal-structured iron at IC conditions and induce elastic anisotropy. Electrical resistivity is much enhanced in comparison to pure hexagonal close-packed (hcp) iron as a result of the enhanced electron correlation effect, supporting the conventional thermal convection model. Moreover, our calculated seismic velocity shows a quantitative match with geologically observed preliminary reference Earth model (PREM) data. We suggest that oxygen is the essential light element to understand and model Earth’s IC

Oxygen-Driven Enhancement of the Electron Correlation in Hexagonal Iron at Earth’s Inner Core Conditions

Earth’s inner core (IC) consists of mainly iron with some light elements. Understanding its structure and related physical properties has been elusive as a result of its required extremely high pressure and temperature conditions. The phase of iron, elastic anisotropy, and density–velocity deficit at the IC have long been questions of great interest. Here, we find that the electron correlation effect is enhanced by oxygen and modifies several important features, including the stability of iron oxides. Oxygen atoms energetically stabilize hexagonal-structured iron at IC conditions and induce elastic anisotropy. Electrical resistivity is much enhanced in comparison to pure hexagonal close-packed (hcp) iron as a result of the enhanced electron correlation effect, supporting the conventional thermal convection model. Moreover, our calculated seismic velocity shows a quantitative match with geologically observed preliminary reference Earth model (PREM) data. We suggest that oxygen is the essential light element to understand and model Earth’s IC

Additional file 1 of Measurement of ferric iron in Chang’e-5 impact glass beads

Additional file 1: Figure S1. Background subtraction method for Fe L-edge EELS. Figure S2. STEM-EDS mapping of foil 2 (sample #084). Figure S3. Repeated measurements of Fe L-edge EELS at different regions of sample #090. Figure S4. Comparative experiment for sample #090 conducted at the same location with dwell times of 0.02 s and 0.1 s, respectively

Topological Ordering of Memory Glass on Extended Length Scales

Identifying ordering in non-crystalline solids has been a focus of natural science since the publication of Zachariasen’s random network theory in 1932, but it still remains as a great challenge of the century. Literature shows that the hierarchical structures, from the short-range order of first-shell polyhedra to the long-range order of translational periodicity, may survive after amorphization. Here, in a piece of AlPO4, or berlinite, we combine X-ray diffraction and stochastic free-energy surface simulations to study its phase transition and structural ordering under pressure. From reversible single crystals to amorphous transitions, we now present an unambiguous view of the topological ordering in the amorphous phase, consisting of a swarm of Carpenter low-symmetry phases with the same topological linkage, trapped in a metastable intermediate stage. We propose that the remaining topological ordering is the origin of the switchable “memory glass” effect. Such topological ordering may hide in many amorphous materials through disordered short atomic displacements

Piezovoltaics from PdH_<i>x</i>

Metal hydrides have wide applications in energy science. A large pressure gradient propels the hydrogen atoms out. A piezovoltaic device, a pressure gradient-driven battery, can therefore be realized when the migrations of protons and electrons are separated by different conductors. Here we investigate the piezovoltaic performance of PdHx with various proton conductors as electrolytes and experimentally detect an output current of ≲40 nA and a voltage of ∼0.8 V for a 3 μg sample. We also demonstrate the escape of hydrogen atoms from a palladium lattice under an increasing pressure gradient using X-ray diffraction. The relationship between piezovoltaics (chemical process) and piezoelectricity (physical process) is like that between a chemical battery and a capacitor. Our work demonstrates the piezovoltaic application of metal hydrides and provides a new way to convert mechanical energy into electrical energy

Piezovoltaics from PdH_<i>x</i>

Metal hydrides have wide applications in energy science. A large pressure gradient propels the hydrogen atoms out. A piezovoltaic device, a pressure gradient-driven battery, can therefore be realized when the migrations of protons and electrons are separated by different conductors. Here we investigate the piezovoltaic performance of PdHx with various proton conductors as electrolytes and experimentally detect an output current of ≲40 nA and a voltage of ∼0.8 V for a 3 μg sample. We also demonstrate the escape of hydrogen atoms from a palladium lattice under an increasing pressure gradient using X-ray diffraction. The relationship between piezovoltaics (chemical process) and piezoelectricity (physical process) is like that between a chemical battery and a capacitor. Our work demonstrates the piezovoltaic application of metal hydrides and provides a new way to convert mechanical energy into electrical energy

Deformation Twinning of a Silver Nanocrystal under High Pressure

Within a high-pressure environment, crystal deformation is controlled by complex processes such as dislocation motion, twinning, and phase transitions, which change materials’ microscopic morphology and alter their properties. Understanding a crystal’s response to external stress provides a unique opportunity for rational tailoring of its functionalities. It is very challenging to track the strain evolution and physical deformation from a single nanoscale crystal under high-pressure stress. Here, we report an in situ three-dimensional mapping of morphology and strain evolutions in a single-crystal silver nanocube within a high-pressure environment using the Bragg Coherent Diffractive Imaging (CDI) method. We observed a continuous lattice distortion, followed by a deformation twining process at a constant pressure. The ability to visualize stress-introduced deformation of nanocrystals with high spatial resolution and prominent strain sensitivity provides an important route for interpreting and engineering novel properties of nanomaterials

Coexistence of Superconductivity and Superhardness in Beryllium Hexaboride Driven by Inherent Multicenter Bonding

Unique multicenter bonding in boron-rich materials leads to the formation of complex structures and intriguing properties. Here global structural searches are performed to unearth the structure of beryllium hexaboride (BeB₆) synthesized decades ago. Three BeB₆ phases (α, β, and γ) were predicted to be stable at ambient and high pressures. The ground state at ambient pressure, α-BeB₆, consists of a strong and uniformly distributed covalent B–B network, which results in exceptional elastic properties and a hardness of 46 GPa comparable to γ-B. Even more surprisingly, α-BeB₆ retains credible electron phonon coupling in the boron sublattice, and is predicted to be superconducting at 9 K. Above 4 GPa, β-BeB₆ is stabilized with alternating boron slabs and triangular beryllium layers analogous to the structure of MgB₂. The β-BeB₆ is predicted to be superconducting at 24 K, similar to Nb₃(Al,Ge). The γ-BeB₆ is stable above 340 GPa. The understanding of intrinsic multicenter-bonding mechanism and related properties demonstrated in the very example of BeB₆ provides new insights for the design of tunable multifunctional materials