Investigation of novel crystal structures of Bi-Sb binaries predicted using the minima hopping method

Novel Ultra-Stable 2D SbBi Alloy Structure with Precise Regulation Ratio Enables Long-Stable Potassium/Lithium-Ion Storage

The inferior cycling stabilities or low capacities of 2D Sb or Bi limit their applications in high-capacity and long-stability potassium/lithium-ion batteries (PIBs/LIBs). Therefore, integrating the synergy of high-capacity Sb and high-stability Bi to fabricate 2D binary alloys is an intriguing and challenging endeavor. Herein, a series of novel 2D binary SbBi alloys with different atomic ratios are fabricated using a simple one-step co-replacement method. Among these fabricated alloys, the 2D-Sb0.6 Bi0.4 anode exhibits high-capacity and ultra-stable potassium and lithium storage performance. Particularly, the 2D-Sb0.6 Bi0.4 anode has a high-stability capacity of 381.1 mAh g-1 after 500 cycles at 0.2 A g-1 (≈87.8% retention) and an ultra-long-cycling stability of 1000 cycles (0.037% decay per cycle) at 1.0 A g-1 in PIBs. Besides, the superior lithium and potassium storage mechanism is revealed by kinetic analysis, in-situ/ex-situ characterization techniques, and theoretical calculations. This mainly originates from the ultra-stable structure and synergistic interaction within the 2D-binary alloy, which significantly alleviates the volume expansion, enhances K+ adsorption energy, and decreases the K+ diffusion energy barrier compared to individual 2D-Bi or 2D-Sb. This study verifies a new scalable design strategy for creating 2D binary (even ternary) alloys, offering valuable insights into their fundamental mechanisms in rechargeable batteries.

Large-area 2D bismuth antimonide with enhanced thermoelectric properties via multiscale electron-phonon decoupling

It is a challenge to obtain high thermoelectric efficiency owing to the conflicting parameters of the materials that are required. In this work, the composition-adjustable 2D bismuth antimonide (Bi_100-xSb_x) is synthesized using an e-beam evaporation system with homemade targets. Engineering multiscale defects is done to optimize the thermoelectric performance in the compound. Sb alloying introduces atomic defects, lattice distortion and increased grain boundary. They drastically decrease the thermal conductivity, with an ultralow value of ∼0.23 W m^-1 K^-1 obtained for the composition with x = 18. It is noticed that the atomic and nanoscale defects do not deteriorate the electrical conductivity (10⁵ S m^-1), and the value is even comparable to the bulk counterpart over a wide composition range (0 ≤ x ≤ 35). Annealing induces pore structure with microscale defects, which increase the Seebeck coefficient by 84% due to the energy barrier. The resultant ZT of 0.13 is enhanced by 420% in the annealed Bi₈₂Sb₁₈ when compared with the as-grown Bi. This work demonstrates a cost-effective and controllable way to decouple electrons and phonons in the thermoelectric field.

Magnetism Modulation for Cryogenic Thermoelectric Enhancements in Fe3O4 Nanoparticle-Incorporated Bi0.85Sb0.15 Nanocomposites

The internal magnetism introduced by the magnetic nanoparticles combined with the external magnetic field can provide an effective way to modulate the thermoelectric (TE) properties of materials. Herein, we comparably investigate the effect of magnetism of Fe₃O₄ nanoparticles (Fe₃O₄-NPs) and the external magnetic field on the cryogenic thermoelectric properties of Fe₃O₄-NP/Bi_0.85Sb_0.15 nanocomposites. With the ferromagnetism-superparamagnetism transition, the Fe₃O₄-NPs in the superparamagnetic state exhibit a stronger magneto-trapped carrier effect, where the electron concentration at high temperature is evidently reduced. With the simultaneous increase of S and reduction of electronic thermal conductivity, a high ZT value of 0.33 at 180 K is obtained for 0.05 wt % Fe₃O₄/Bi_0.85Sb_0.15. Meanwhile, under the external magnetic field, the magnetoresistance of the composites is suppressed by Fe₃O₄-NPs, which results in a remarkable enhancement of the electronic transport performance. Consequently, the highest ZT value of 0.48 at 220 K under 1 T is achieved for 0.1 wt % Fe₃O₄-NPs/Bi_0.85Sb_0.15, increased by 55% compared with that of the matrix. A single-leg device is prepared using 0.1 wt % Fe₃O₄-NP/Bi_0.85Sb_0.15 nanocomposites. Its cooling temperature difference at 180 K reaches 1.3 and 3.2 K under 0 and 1 T when applying 300 mA current, increased by 20 and 46% compared with that of the matrix, respectively. This work suggests that magnetism modulation with introducing magnetic nanoparticles will enhance the TE and magneto-TE performance of composite materials.

Understanding Topological Insulators in Real Space

A real space understanding of the Su–Schrieffer–Heeger model of polyacetylene is introduced thanks to delocalization indices defined within the quantum theory of atoms in molecules. This approach enables to go beyond the analysis of electron localization usually enabled by topological insulator indices—such as IPR—enabling to differentiate between trivial and topological insulator phases. The approach is based on analyzing the electron delocalization between second neighbors, thus highlighting the relevance of the sublattices induced by chiral symmetry. Moreover, the second neighbor delocalization index, δi,i+2, also enables to identify the presence of chirality and when it is broken by doping or by eliminating atom pairs (as in the case of odd number of atoms chains). Hints to identify bulk behavior thanks to δ1,3 are also provided. Overall, we present a very simple, orbital invariant visualization tool that should help the analysis of chirality (independently of the crystallinity of the system) as well as spreading the concepts of topological behavior thanks to its relationship with well-known chemical concepts.

Anomalous negative longitudinal magnetoresistance and violation of Ohm's law deep in the topological insulating regime in Bi[Formula: see text]Sb[Formula: see text]

Bi[Formula: see text]Sb[Formula: see text] is a topological insulator (TI) for [Formula: see text]-0.20. Close to the Topological phase transition at [Formula: see text], a magnetic field induced Weyl semi-metal (WSM) state is stabilized due to the splitting of the Dirac cone into two Weyl cones of opposite chirality. A signature of the Weyl state is the observation of a Chiral anomaly [negative longitudinal magnetoresistance (LMR)] and a violation of the Ohm's law (non-linear [Formula: see text]). We report the unexpected discovery of Chiral anomaly-like features in the whole range ([Formula: see text]) of the TI state. This points to a field induced WSM state in an extended x range and not just near the topological transition at [Formula: see text]. Surprisingly, the strongest Weyl phase is found at [Formula: see text] with a non-saturating negative LMR much larger than observed for [Formula: see text]. The negative LMR vanishes rapidly with increasing angle between B and I. Additionally, non-linear I-V is found for [Formula: see text] indicating a violation of Ohm's law. This unexpected observation of a strong Weyl state in the whole TI regime in Bi[Formula: see text]Sb[Formula: see text] points to a gap in our understanding of the detailed crystal and electronic structure evolution in this alloy system.

Two-Dimensional Giant Tunable Rashba Semiconductors with Two-Atom-Thick Buckled Honeycomb Structure

Spin field-effect transistors (SFETs) based on the Rashba effect could manipulate the spin of electrons electrically, while seeking desirable Rashba semiconductors with large Rashba constant and strong electric-field response, to preserve spin coherence remains a key challenge. Herein, we propose a series of 2D Rashba semiconductors with two-atom-thick buckled honeycomb structure (BHS) according to high-throughput first-principles density functional theory calculations. BHS semiconductors show large Rashba constants that are favorable to be integrated into nanodevices superior to conventional bulk materials, and they can be fabricated by mechanical exfoliation or chemical vapor deposition. In particular, 2D AlBi monolayer has the largest Rashba constant (2.77 eVÅ) of all 2D Rashba materials. Furthermore, 2D BiSb monolayer is a promising candidate for SFETs due to its large Rashba constant (1.94 eVÅ) and strong electric field response (0.92 eŲ). Our designed 2D-BiSb-SFET shows shorter spin channel length (42 nm with strain) than conventional SFETs (2-5 μm).

Low-Energy Phases of Bi Monolayer Predicted by Structure Search in Two Dimensions

We employ an ab-initio structure search algorithm to explore the configurational space of bismuth in quasi-two dimensions. A confinement potential is introduced to restrict the movement of atoms within a predefined thickness to find the stable and metastable forms of monolayer Bi. In addition to the two known low-energy structures (puckered monoclinic and buckled hexagonal), our calculations predict three new phases: α, β, and γ. Each phase exhibits peculiar electronic properties, ranging from metallic (α and γ) to semiconducting (puckered monoclinic, buckled hexagonal, and β) monolayers. Topologically nontrivial features are predicted for buckled hexagonal and γ phases. We also remark on the role of 5d electrons on the electronic properties of Bi monolayer. We conclude that Bi provides a rich playground to study distortion-mediated metal-insulator phase transitions in quasi-2D.

Structure dependent optoelectronic properties of monolayer antimonene, bismuthene and their binary compound

The absorption spectra of antimonene, bismuthene, and their BiSb binary compound are revealed.

Structural search for stable Mg–Ca alloys accelerated with a neural network interatomic model

We have combined a neural network formalism with metaheuristic structural global search algorithms to systematically screen the Mg–Ca binary system for new (meta)stable alloys.

Strain induced quantum spin Hall insulator in monolayer β-BiSb from first-principles study

Topological insulator (TI) is a peculiar phase of matter exhibiting excellent quantum transport properties with potential applications in lower-power-consuming electronic devices.

Controlling the magnetic and optical responses of a MoS2 monolayer by lanthanide substitutional doping: a first-principles study

The absorption spectrum and TDOS of lanthanide doped MoS₂ for the E-field parallel and perpendicular to the xy-plane.