Improved Lithium Diffusion in Anion-Substituted Li₇TaO₆

One approach to enhance the conductivity of a lithium-containing material is to widen the diffusion channel, such as the case of the superionic material Li10GeP2S6. This work unravels the enhanced diffusivity of Li+ in Li7TaS6 and Li7TaSe6, which are based on the known Li7TaO6 superionic conductor. Using density functional theory, we calculate the electronic and structural properties of the three materials and utilize ab initio molecular dynamics simulations to model the diffusion dynamics. Both Li7TaS6 and Li7TaSe6 are shown to exhibit an order of magnitude improvement in the diffusion coefficient relative to the parent material and a slight drop in their corresponding activation barriers. These materials are potential candidates for application in lithium solid-state electrolytes, with performance that is competitive with Li10GeP2S6

Twist-Dependent Electron Charge Transfer and Transport in Phosphorene–Graphene Heterobilayers

In this work, we explore the impact of twisting (rotational stacking) on the vertical charge transfer in a graphene–phosphorene bilayer using density functional theory (DFT) and on electron transport in the plane of the bilayer using DFT and the non-equilibrium Green’s function approach. We examine the bilayers with twist angles 0, 9.1, 13.3, and 44.1° and find a significant drop in charge transfer when the twist angle changes from 0 to >0°. We also identify an anisotropy of the current with regard to the twist angle, as well as direction, in the plane of the bilayer structures. Such interesting features could have an impact on enhancing the applications of two-dimensional twisted structures in nano-electronics

Blocking Directional Lithium Diffusion in Solid-State Electrolytes at the Interface: First-Principles Insights into the Impact of the Space Charge Layer

Understanding the degradation mechanisms in solid-state lithium-ion batteries at interfaces is fundamental for improving battery performance and for designing recycling methodologies for batteries. A key source of battery degradation is the presence of the space charge layer at the solid-state electrolyte–electrode interface and the impact that this layer has on the thermodynamics of the electrolyte structure. Currently, Li10GeP2S12 in its pristine form has one of the highest lithium conductivities and has been used as a template for designing even higher conductivity derived structures. However, being an ionic material with mostly linear diffusion, it is prone to path-blocker defects, which we show here to be especially prevalent in the space charge layer. We analyze the thermodynamic properties of a number of path-blocker defects using density functional theory and their potential crystal decomposition and find that the presence of an electrostatic potential in the space charge layer elevates the likelihood of existence of these defects, which otherwise would not be likely to form in the bulk of the electrolyte away from electrodes. We use ab initio molecular dynamics to assess the impact of these defects on the diffusivity of the crystal and find that they all reduce the lithium diffusivity. While our work focuses on Li10GeP2S12, it is relevant to any solid-state electrolyte with mainly linear diffusion

Machine Learning-Aided Exploration of Ultrahard Materials

Ultrahard materials are an essential component in a wide range of industrial applications. In this work, we introduce novel machine learning (ML) features for the prediction of the elastic moduli of materials, from which the Vickers hardness can be calculated. By applying the trained ML models on a space of ∼110,000 materials, these features successfully predict the elastic moduli for a range of materials. This enables the identification of materials with high Vickers hardness, as validated by comparing the predictions against the density functional theory calculations of the moduli. We further explored the predicted moduli by examining several classes of materials with interesting mechanical properties, including binary and ternary alloys, aluminum and magnesium alloys, metal borides, carbides and nitrides, and metal hydrides. Based on our ML models, we identify a number of ultrahard compounds in the B–C and B–C–N chemical spaces and ultrahard ultralight-weight magnesium alloys Mg3Zn and Mg3Cd. We also observe the inverse of the hydrogen embrittlement effect in a number of metal carbides, where the introduction of hydrogen into metal carbides increases their hardness, and find that substitutional doping of Al in transition-metal borides can yield lighter materials without compromising the thermodynamic stability or the hardness of the material

Strain Modulation of Optoelectronic Properties in Nanolayered Black Phosphorus: Implications for Strain-Engineered 2D Material Systems

Strain engineering is an exciting direct approach to control the key intrinsic properties of two-dimensional (2D) materials. However, fabrication complexities arising from weak van der Waals interaction-induced slippage, coupled with mechanical breakdown of metal electrodes, have prevented fundamental investigations into strain effects on electrical and optoelectronic characteristics of these material systems. To overcome this limitation, we report a simple prestretch fabrication technique that allowed us to demonstrate a functional multilayer black phosphorus (BP)-based device on a stretchable elastomeric platform. By applying a uniaxial compressive strain of up to 10%, we reveal that mechanical strain can be effectively used to modulate the electronic and optical properties of nanolayered BP. This simple strategy can be extended well-beyond BP to other 2D materials, creating opportunities for fundamental investigations into strain effects in 2D material systems and potential applications in strain-engineered sensors for optical synapse applications

Exploring Coordination of Neodymium in Ionic Liquid: Insights to Guide Sustainable Recovery

Neodymium is a critical metal essential for advancing sustainable clean energy technologies, as it is a crucial component in the manufacturing of NdFeB permanent magnets, part of wind turbines, electric vehicles, and advanced electronics. Its recovery from secondary sources using electrochemical deposition in ionic liquids has the potential to sustainably achieve a closed-loop alternative to obtain the metal. The presence of water in low, specific concentrations in ionic liquid has been previously shown to catalyze electrodeposition of Nd with amplified current densities and easier reduction of Nd3+, but the structure(s) of the metal/mixed-ligand species that led to this amplification was previously only hypothesized. Stringently benchmarked quantum chemical calculations reveal a complex potential energy landscape that underpins the structural transformations arising from the introduction of water into the coordination sphere of Nd3+ surrounded by bis­(trifluoromethanesulfonyl)­imide (TFSI) anions. Three distinct changes were observed in the Nd3+-TFSI– complexes upon addition of water: (i) cis/trans transformation of TFSI, (ii) transition from bidentate to monodentate TFSI– coordination, and (iii) displacement of TFSI– ligands by water. Energetic analyses of these structural changes can explain experimentally observed water-loading effects regarding the ease of electrochemical reduction of Nd3+ and its deposition. These outcomes provide a platform for tuning ionic liquid media compositions to enhance rare-earth metal recovery

Reactive Oxygen Species Sequestration Induced Synthesis of β‑PbO and Its Polymorphic Transformation to α‑PbO at Atomically Thin Regimes

The emergence of attractive properties in materials at atomically thin regimes has seen an ongoing interest in two-dimensional (2D) materials. An aspect that has lacked focused attention is the effect of 2D material thickness on its crystal structure. As several layered materials naturally exist in mixed metastable phases, it raises an important question of whether a specific polymorph of these mixed-phase materials will be favored at atomically thin limits. This work attempts to address this issue by employing lead monoxide as a model 2D polymorphic system. We propose a reactive oxygen species (ROS) sequestration-mediated liquid-phase exfoliation (LPE) strategy for the facile synthesis of ultrathin PbO. This is followed by a suite of microscopic and spectroscopic analyses of the PbO nanosheets that reveals the polymorphic transformation of orthorhombic (β) PbO to its tetragonal (α) analogue with reduction in nanosheet thickness. The transformation process reveals an interesting crystal structure of ultrathin 2D PbO where [001]-oriented domains of α-PbO coexist alongside [100]-oriented regions of β-PbO. Density functional theory (DFT) calculations support our experimental data by revealing a higher thermodynamic stability of the tetragonal phase in PbO monolayers. These findings are likely to instigate interest in carefully evaluating the crystal structures of ultrathin 2D materials while promoting research in understanding the phase transformation across a range of 2D crystals

Alkali-Assisted Hydrothermal Exfoliation and Surfactant-Driven Functionalization of <i>h</i>‑BN Nanosheets for Lubrication Enhancement

Intrinsic low shear strength, excellent mechanical properties, and high thermal conductivity of two-dimensional h-BN nanomaterials make them promising alternatives to conventional metal-/phosphorus-/sulfur-based additives for the development of eco-friendly lubricant formulation. However, the poor dispersibility of h-BN nanomaterials in lubricating oils is a major challenge. Herein, a facile approach of strong alkali-assisted hydrothermal exfoliation and defect-sensitive etching of h-BN powder is demonstrated. The cetyltrimethylammonium bromide (CTAB) is grafted on the active and polar sites of h-BN nanosheets (h-BNNSs). DFT calculations, along with FTIR and XPS results, confirmed the synthesis of h-BNNS-CTAB, which showed good dispersibility in SN-150 mineral lube base oil. The uninterrupted supply of highly dispersible minute dose of h-BNNS-CTAB (0.003 wt %) to tribo interfaces of steel balls improved the lubrication properties of lube oil by decreasing friction (34%) and wear volume (75%). The enhanced tribo-performance is attributed to low shear strength arising from weakly stacked atomic lamellae in h-BNNS-CTAB and the tribo-induced deposition of h-BN lamellae on the contact interfaces of steel balls. The present work proposes a novel strategy for developing h-BNNS-based high-performance lubricant formulation, which can effectively minimize frictional energy and material losses