Physics

The search for room-temperature ferromagnetic two-dimensional materials is crucial for the development of future functional spintronic devices. In this study, combining a global minimum search method of the free energy surfaces by the CALYPSO software, we have predicted a two-dimensional cobalt structure. First-principles calculations demonstrate that the structure is a stable ferromagnetic metal exhibiting in-plane magnetic anisotropy, with an estimated Curie temperature of 1001 K significantly exceeding room temperature. Furthermore, the structure shows remarkable resistance to external strain, maintaining its ferromagnetic ground state and excellent stability under biaxial strains ranging from \ensuremath{-}4% to 5%. These findings indicate that the structure holds promising application prospects in spintronic devices.

We compute the thermodynamic phase diagram of 17 elemental metals with hexagonal-close-packed (hcp), face-centered-cubic (fcc), and body-centered-cubic (bcc) crystal structures using finite-temperature density functional theory. Helmholtz free-energy differences between competing hcp, fcc, and bcc phases are evaluated as functions of electronic temperature up to 7 eV, allowing us to identify solid-solid phase transitions driven by electronic entropy. The systems studied include Zr, Ti, Cd, Zn, Co, and Mg (hcp); Ni, Cu, Ag, Al, Pt, and Pb (fcc); and Cr, W, V, Nb, and Mo (bcc) in their ground-state structures. From the free-energy crossings, we extract the transition electronic temperatures and analyze systematic trends across the metallic systems. We found that all the studied systems go through one or two solid-solid phase transitions caused purely by electronic entropy except Mg and Pb. Our results establish electronic entropy as a key factor governing structural stability in metals under strong electronic excitation.

The intrinsically low thermal conductivity of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>β</a:mi> <a:mrow> <a:mo>−</a:mo> <a:mi mathvariant="normal">G</a:mi> </a:mrow> <a:msub> <a:mi mathvariant="normal">a</a:mi> <a:mn>2</a:mn> </a:msub> <a:msub> <a:mi mathvariant="normal">O</a:mi> <a:mn>3</a:mn> </a:msub> </a:mrow> </a:math> poses a major challenge for high-power and high-frequency electronic applications. This issue becomes more severe in the presence of defects, which further suppress heat dissipation, exacerbate self-heating, and degrade device performance. In this work, we develop an efficient machine learning potential (MLP) based on a deep neural network model for accurately describing pristine and point-defective <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mi>β</e:mi> <e:mrow> <e:mo>−</e:mo> <e:mi mathvariant="normal">G</e:mi> </e:mrow> <e:msub> <e:mi mathvariant="normal">a</e:mi> <e:mn>2</e:mn> </e:msub> <e:msub> <e:mi mathvariant="normal">O</e:mi> <e:mn>3</e:mn> </e:msub> </e:mrow> </e:math> . Using equilibrium molecular dynamics (EMD) simulations, we quantify the reduction in thermal conductivity induced by intrinsic point defects. Our results demonstrate that Ga interstitials exert the strongest suppression, decreasing the thermal conductivity by 79.5%. Moreover, Ga-related defects generally have a more pronounced impact than O-related defects. This behavior originates from the enhanced vibrations of weakly bonded Ga atoms, increased phonon anharmonicity, and a substantial reduction in the group velocity of low-frequency phonons. These results provide atomic-level insight into thermal transport in defective <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:mi>β</i:mi> <i:mrow> <i:mo>−</i:mo> <i:mi mathvariant="normal">G</i:mi> </i:mrow> <i:msub> <i:mi mathvariant="normal">a</i:mi> <i:mn>2</i:mn> </i:msub> <i:msub> <i:mi mathvariant="normal">O</i:mi> <i:mn>3</i:mn> </i:msub> </i:mrow> </i:math> , offering guidance for thermal-management strategies and establishing a general workflow for investigating thermal physics in complex semiconductor materials.

While intrinsic two-dimensional (2D) ferromagnetic (FM) materials hold great promise for spintronic applications, external control over both electrical and magnetic properties is crucial. Here, we demonstrate effective modulation of electronic and magnetic characteristics of ${\mathrm{Cr}}_{2}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$ (CST) through ionic liquid gating (ILG). Upon electron doping via ILG, CST undergoes a semiconductor-to-metal transition, accompanied by remarkable enhancements in Curie temperature (${T}_{\mathrm{c}}$, from 33 K to 110 K) and coercive field (${H}_{\mathrm{c}}$, from 1.4 mT to 50 mT). Moreover, under high doping levels, the magnetic easy axis can be electrically switched from the out-of-plane to the in-plane direction. Theoretical calculations suggest a possible scenario in which electron doping strengthens FM coupling through a double-exchange mechanism between mixed-valence Cr ions, thereby boosting ${T}_{\mathrm{c}}$. These findings highlight ILG as a versatile strategy for tailoring magnetism in 2D ferromagnets and offering pathways for next-generation spintronic devices.

ABSTRACT Solid oxide electrochemical cells (SOC), encompassing fuel‐cell, electrolysis, and reversible operating modes, represent a pivotal technology for high‐efficiency conversion between electrical energy and chemical fuels. However, practical deployment at intermediate‐temperatures (IT, 600–800°C) is constrained by intertwined limitations in ionic transport, surface reaction kinetics, and thermo–chemical stability. This review summarizes and analyzes the recent developments in SOC electrodes and electrolytes through a unified structure‐defect‐property‐durability framework. Emphasis is placed on how crystal symmetry, lattice distortions, and defect chemistry dictate charge‐carrier concentrations, oxygen and proton migration pathways, and interfacial compatibility under realistic oxidizing and reducing environments. By correlating electrochemical performance with oxygen‐vacancy formation energetics, transport coefficients, and degradation processes such as cation segregation and secondary‐phase evolution, the potential of different materials for SOC was further analyzed. Finally, prospective strategies involving multifunctional electrolyte architectures, defect and interface‐engineered electrodes, and multiscale microstructural control are outlined, offering guidance to the rational design of durable, high‐performance SOC systems capable of sustained operation in the IT regime.

ABSTRACT Inverted perovskite solar cells (PSCs) garner extensive attention for improved operating stability but the power conversion efficiency (PCE) still lags behind its theoretical limit. The energetic losses responsible for this PCE deficit primarily stem from non‐radiative recombination induced by crystalline defect states in the perovskite bulk and at interfaces, coupled with inefficient carrier extraction caused by energy level mismatches across adjacent interfaces. Here, a tailored additive engineering strategy is proposed by designing a planar molecule 4‐Cyanobenzamide (4‐CBA) that features multifunctional active sites for the perovskite precursor. The dual electron‐rich moieties C═O and C≡N can strongly anchor uncoordinated Pb 2+ , thereby stabilizing the [PbI 6 ] 4− framework and alleviating internal residual strain. The enhanced ─NH 2 group, acting as both a hydrogen bond acceptor and donor, compensates for vacancy defects through interactions with FA + /I − , regulating the preferential growth of crystal planes, and reducing non‐radiative recombination. Notably, 4‐CBA with a planar structural orientation can also tune energy level matching, minimize interfacial steric hindrance, and optimize carrier transport balance. The champion PSC device based on 4‐CBA achieves a PCE of 26.25% and an exceptional fill factor ( FF ) of 85.97%.

ABSTRACT Aqueous zinc‐ion batteries hold great promise for sustainable energy storage, yet uncontrolled Zn dendrite formation critically limits their cyclability. To address this issue, a type‐II band alignment‐driven bidirectional heterojunction array is engineered as a multifunctional interface layer for the Zn anode. This multiscale vertical array architecture simultaneously regulates electric field distribution, homogenizes Zn 2+ ion flux, and mitigates electrodeposition stress, thereby promoting uniform and reversible Zn plating/stripping. As a result, the modified anode achieves a high depth of discharge of 85.5% and sustains stable cycling for over 350 h at 5 mA cm −2 /5 mAh cm −2 . When paired with an iodine‐based cathode, the full cell retains 184.4 mAh g −1 after 10 000 cycles. The use of readily available materials, combined with a scalable fabrication approach and rationally designed multiscale interface, offers a practical and inspiring strategy toward high‐performance zinc‐based energy storage systems.

ABSTRACT Conventional glass fiber (GF) separators have large pores with a wide size distribution, which exacerbate dendrite formation in aqueous Zn‐ion batteries via irregular ionic flux. Herein, a repetitive interfacial assembly (RIA) method is introduced to prepare a hydrogel separator with interconnected anionic nanochannels (ANCs) surrounding the 3D network of bacterial cellulose (BC) nanofibers. This enables conformal coating of the BC nanofibers with nanometer‐thick, carboxylate (─COO − )‐rich polymeric layers via bottom‐up assembly and growth. The optimal sample exhibits an ionic conductivity of 40.4 mS cm −1 and a high Zn 2+ transference number of 0.75, which is attributed to the rapid migration of partially desolvated Zn ions via transient coordination with ─COO − in the ANCs. Furthermore, the homogeneous ion flux from the nanostructured RIA hydrogel and the decreased desolvation energy of the less hydrated Zn ions synergistically improve the charge transfer at the Zn‐metal electrode, thereby resulting in smooth and planar Zn deposition and dendrite suppression. Compared to the bare BC and GF, the RIA‐based Zn//Zn symmetric cell operates stably for 1000 h at 5 mA cm −2 and 1 mA h cm −2 , and the Zn//NaV 3 O 8 ·1.5H 2 O full cell exhibits superior cycling stability and rate capability.

ABSTRACT The performance of tin‐lead perovskite solar cells (PSCs) is limited by perovskite crystallographic inhomogeneity and interfacial defect‐induced non‐radiative recombination. Besides, the grain growth orientation is more difficult to control compared to pure lead perovskite. We developed 6‐hydroxypyridazine‐3‐carboxylic acid (HCA) as an additive, whose diazine ring nitrogen and carboxyl C═O can prefer coordinating with Sn 2+ ions, thereby synchronizing the crystallization kinetics of tin and lead components. This molecule can also induce the crystallization of perovskite along the (100) plane, promoting the formation of vertical‐through‐grain morphology to reduce defect density and enhance charge transport. Furthermore, the PEDOT:PSS substrate was modified with a SAM molecule, (4‐(6‐methoxy‐9H‐thieno[2′,3′:4,5]thieno[3,2‐b]indol‐9‐yl)butyl)phosphonic acid (MeOK), which forms close π‐π stacking with PEDOT. This interaction reduces the PSS content on the PEDOT:PSS surface, thereby mitigating acidic corrosion for prolonged stability. Concurrently, the molecular dipole of MeOK optimizes the energy level alignment and suppresses non‐radiative recombination of the buried interface. The devices fabricated based on this synergistic strategy achieved a power conversion efficiency (PCE) of 24.08%. The corresponding all‐perovskite tandem solar cells reached a PCE of 28.81%, and after 1000 h of maximum power point tracking, they maintained 90% of their initial efficiency.

ABSTRACT The growing adoption of green energy has led to an increasing demand for efficient energy storage solutions. Aqueous zinc‐ion batteries (AZIBs), known for their intrinsic safety, environmental compatibility, and cost efficiency, are regarded as promising candidates. However, challenges such as dendritic growth, hydrogen evolution, and anode corrosion hinder their commercialization. Electrolyte engineering has emerged as a widely adopted and effective strategy to improve battery performance. Specifically, trace‐amount additives that selectively target the surface have recently attracted significant attention due to their ability to deliver substantial interfacial improvements while preserving the desirable bulk properties of the electrolyte. Here, we systematically summarize trace‐amount additives based on their distinct mechanisms—analyzing structure–function relationships—focusing on both experimental and computational approaches to achieve effective additives. We also present representative examples to further summarize the underlying reasons why these additives remain effective even at trace amounts. Finally, we propose a working definition of “trace‐amount additives” and provide design strategies for future research to enable low‐cost and environmentally sustainable AZIB systems with competitive performance.

ABSTRACT Solid polymer electrolytes (SPEs) are promising for solid‐state lithium (Li) metal batteries due to their enhanced safety and high energy density. However, the inherent trade‐off between ionic conductivity and mechanical strength severely limits their practical application. Herein, we report a dense fluorinated composite polymer electrolyte (d‐FCPE) that simultaneously addresses the challenges of mechanical robustness, ionic conductivity, and interfacial stability in Li metal batteries. The dense architecture endows the d‐FCPE with favorable mechanical strength, elongation, and adhesion, ensuring superior processability and intimate interfacial contact. Concurrently, the fluorinated composite polymer suppresses electrolyte crystallinity and regulates the ion solvation structure, thereby achieving a high ionic conductivity of 8.6 × 10 −4 S cm −1 at room temperature. Crucially, the integrated dense structure promotes the in‐situ formation of a robust, LiF‐enriched solid electrolyte interphase, which effectively suppresses lithium dendrite growth and enhances electrochemical cycling stability. Consequently, the Li|d‐FCPE|Li symmetric cell exhibits stable cycling for over 4500 h at 0.5 mA cm −2 . The batteries using LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode and d‐FCPE deliver a long cycle life, maintaining capacity retention of 83.2% (0.5C) and 84.5% (2C) after 1000 cycles. This work highlights the pivotal role of fluorination‐assisted densification in developing high‐performance SPEs for advanced solid‐state energy storage.

Converting harmful nitrate waste into value-added chemicals represents a promising alternative for achieving the electrocatalytic upgrading of NO3- and maintaining the global nitrogen balance. Nonetheless, improving the electrochemical performance and revealing reaction mechanisms still requires further investigation to meet the practical application requirements. Herein, we summarize the development of electrochemical NO3- reduction reaction (NO3RR) and C-N coupling reaction under pulsed-potential conditions. In the section on NO3RR, the electrocatalytic reaction systems for direct conversion of NO3- to NH3 are summarized. In the section on coupling, the C-N coupling reactions of NO3- with CO2 for urea synthesis, and with organic molecules for amino compounds synthesis are reviewed. The corresponding reaction mechanisms for different reaction systems are compared with the aid of theoretical calculations. Finally, the challenges and future perspectives are proposed. The pulsed-potential electrolysis for nitrate reduction not only increases the concentration of the local NO3-, key reactant, and intermediate species, but also restores the oxidation state of the active sites, providing guidance and reference for a nitrogen economy.

Abstract Superconducting resonator parametric amplifiers are potentially important components for a wide variety of fundamental physics experiments and utilitarian applications. We propose and realise an operating scheme that achieves amplification through the use of non-degenerate pumps, which addresses two key challenges in the design of parametric amplifiers: non-continuous gain across the amplification band and pump tone removal. We have experimentally demonstrated the non-degenerate pumping scheme using a half-wave resonator amplifier based on NbN thin-film, and measured a peak gain of 26 dB and 3-dB bandwidth of 0.5 MHz. The two non-degenerate pump tones were positioned $$\sim 10$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:math> bandwidths above and below the frequency at which peak gain occurs. We have found the non-degenerate pumping scheme to be more stable compared to the usual degenerate pumping scheme in terms of gain drift over time, by a factor of 4. This scheme also retains the usual flexibility of NbN resonator parametric amplifiers in terms of reliable amplification in a $$\sim 4$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:math> K environment, and is suitable for cross-harmonic amplification. The use of pump tones at different frequencies allows phase-sensitive amplification when the signal tone is degenerate with the idler tone. A gain of 23 dB and squeezing ratio of 6 dB were measured.

By means of full-wavelength near-field plasmon mapping, gradual evolutions of multipole coupling modes in Ag nanoparticle homodimer and heterodimer hotspots are witnessed. According to the symmetry and distributions of the compressed surface charge lobes, various complicated high-order coupling modes are identified, which turns out to be beyond the prediction of general plasmon hybridization model. Specifically, different intermediate states between the bonding dipole-dipole coupling and bonding quadrupole-quadrupole coupling can be observed. Our results provide an essential understanding of the dimer hotspot systems and pave a new way for the exploration of multipole coupling effects in plasmonic complexes.