Influence of Oxidation on Structure, Performance, and Application of Metallic Glasses

Owing to their unique structure and outstanding properties, metallic glasses are a novel class of structural and functional materials with vast application prospects. However, the metastable amorphous structures and chemical activity of metallic glass constituent elements lead to frequent oxidation during preparation, processing, and application. Comprehensively understanding the oxidation behaviors and underlying mechanisms of metallic glasses is essential for gaining knowledge of metallic glass structures and properties and for promoting engineering applications. Although many studies have examined these issues, more investigations are still required to explore potential industrial applications of metallic glasses. Here, recent research on metallic glass oxidation is consolidated by summarizing the oxidation influence on metallic glass structure, performance, and application and the possibilities and feasibility of oxidizing metallic glasses to reinforce materials or develop material systems are discussed.

Intrinsic Electron Localization of Metastable MoS2 Boosts Electrocatalytic Nitrogen Reduction to Ammonia

The advancement of efficient electrocatalysts toward the nitrogen reduction reaction (NRR) is critical in sustainable ammonia synthesis under ambient pressure and temperature. Manipulating the electronic configuration of electrocatalysts is particularly vital to form metal-nitrogen (MN) bonds during the NRR through regulating the active electronic states of sites. Here, in sharp contrast to stable 2H MoS₂ without metal chains, MoMo bonding in metastable polymorphs of MoS₂ bulk (zigzag chain in the 1T' phase and diamond chain in the 1T″' phase) is discovered to significantly increase intrinsic electron localization around the metal chains. This can enhance the charge transfer from the adsorbed nitrogen molecule to the metal chains, allowing for boosted NRR kinetics. The electrochemical experiments show that the NH₃ yield rate and the faradaic efficiency of the metastable 1T″' MoS₂ rich with abundant Mo-Mo bonds are about 9 and 12 times above average than those of 2H MoS₂ , correspondingly. Theoretical simulations reveal the high local electron density surrounding the MoMo chains and sites can promote π back-donation, which is beneficial for increasing nitrogen adsorption, strengthening the MN bonds, and reducing the cleavage barrier of the triple NN bond.

Reversing the Irreversible: Thermodynamic Stabilization of LiAlH4 Nanoconfined Within a Nitrogen-Doped Carbon Host

A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH₄ as an exemplar, we demonstrate an alternative approach to the thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH₄@NCMK-3 material releases H₂ at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li₃AlH₆ intermediate observed in bulk. Moreover, >80% of LiAlH₄ can be regenerated under 100 MPa H₂, a feat previously thought to be impossible. Nitrogen sites are critical to these improvements, as no reversibility is observed with undoped CMK-3. Density functional theory predicts a drastically reduced Al-H bond dissociation energy and supports the observed change in the reaction pathway. The calculations also provide a rationale for the solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.

Discovery of Cu3Pb

Materials discovery enables both realization and understanding of new, exotic, physical phenomena. An emerging approach to the discovery of novel phases is high-pressure synthesis within diamond anvil cells, thereby enabling in situ monitoring of phase formation. Now, the discovery via high-pressure synthesis of the first intermetallic compound in the Cu-Pb system, Cu₃Pb is reported. Cu₃Pb is notably the first structurally characterized mid- to late-first-row transition-metal plumbide. The structure of Cu₃Pb can be envisioned as a direct mixture of the two elemental lattices. From this new framework, we gain insight into the structure as a function of pressure and hypothesize that the high-pressure polymorph of lead is a possible prerequisite for the formation of Cu₃Pb. Crucially, electronic structure computations reveal band crossings near the Fermi level, suggesting that chemically doped Cu₃Pb could be a topologically nontrivial material.

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

Rapid Growth of Crystalline Mn5O8 by Self-Limited Multilayer Deposition using Mn(EtCp)2 and O3

This work investigates the use of ozone as a post-treatment of ALD-grown MnO and as a coreactant with bis(ethylcyclopentadienyl)manganese (Mn(EtCp)2) in ALD-like film growth. In situ quartz crystal microbalance measurements are used to monitor the mass changes during growth, which are coupled with ex situ materials characterization following deposition to evaluate the resulting film composition and structure. We determined that during O3 post-treatment of ALD-grown MnO, O3 oxidizes the near-surface region corresponding to a conversion of 22 Å of the MnO film to MnO2. Following oxidation by O3, exposure of Mn(EtCp)2 results in mass gains of over 300 ng/cm(2), which exceeds the expected mass gain for reaction of the Mn(EtCp)2 precursor with surface hydroxyls by over four times. We attribute this high mass gain to adsorbed Mn(EtCp)2 shedding its EtCp ligands at the surface and releasing Mn(II) ions which subsequently diffuse into the bulk film and partially reduce the oxidized film back to MnO. These Mn(EtCp)2 and O3 reactions are combined in sequential steps with (a) Mn(EtCp)2 reacting at the surface of an O-rich layer, shedding its two EtCp ligands and freeing Mn(II) to diffuse into the film followed by (b) O3 oxidizing the film surface and withdrawing Mn from the subsurface to create an O-rich layer. This deposition process results in self-limiting multilayer deposition of crystalline Mn5O8 films with a density of 4.7 g/cm(3) and an anomalously high growth rate of 5.7 Å/cycle. Mn5O8 is a metastable phase of manganese oxide which possesses an intermediate composition between the alternating MnO and MnO2 compositions of the near-surface during the Mn(EtCp)2 and O3 exposures.

Conceptual inorganic materials discovery - a road map

Synthesis of novel solids, which is a pivotal starting point in innovative materials research, is markedly impeded by the lack of predictability. A conception is presented that enables syntheses of new materials to be rationally planned. The approach is based on the atomic configuration space, and the potential energies associated to the atomic arrangements. Each minimum of the respective hyperspace of potential energy corresponds to a chemical compound capable of existence. Thus the whole realm of known and not-yet-known chemical compounds is represented in virtuo on that energy landscape. From this view it follows further that the full sets of the corresponding materials' properties are pre-determined. Within the scope of the "Energy Landscape Concept of Chemical Matter" presented, targets for synthesis are identified in a rational manner by searching the underlying potential energy landscapes for (meta)stable candidates computationally. Subsequently, the gained information are transferred to finite temperatures, which enables phase diagrams to be calculated, including metastable manifestations of matter, from first principles. The subsequent steps in materials discovery, e.g., assessing the properties and the impact of defects on the performance of the solids predicted are addressed briefly. The approach presented is complete and physically consistent; its feasibility has been proven and validated experimentally.

Lithium potential variations for metastable materials: case study of nanocrystalline and amorphous LiFePO4

Much attention has been paid to metastable materials in the lithium battery field, especially to nanocrystalline and amorphous materials. Nonetheless, fundamental issues such as lithium potential variations have not been pertinently addressed. Using LiFePO4 as a model system, we inspect such lithium potential variations for various lithium storage modes and evaluate them thermodynamically. The conclusions of this work are essential for an adequate understanding of the behavior of electrode materials and even helpful in the search for new energy materials.