Anisotropic Strain-Tailoring Nonlinear Optical Response in van der Waals NbOI2.

Two-dimensional (2D) NbOI2 demonstrates significant second-harmonic generation (SHG) with a high conversion efficiency. To unlock its full potential in practical applications, it is desirable to modulate the SHG behavior while utilizing the intrinsic lattice anisotropy. Here, we demonstrate direction-specific modulation of the SHG response in NbOI2 by applying anisotropic strain with respect to the intrinsic lattice orientations, where more than 2-fold enhancement in the SHG intensity is achieved under strain along the polar axis. The strain-driven SHG evolution is attributed to the strengthened built-in piezoelectric field (polar axis) and the enlarged Peierls distortions (nonpolar axis). Moreover, we provide quantifications of the correlation between strain and SHG intensity in terms of the susceptibility tensor. Our results demonstrate the effective coupling of orientation-specific strain to the anisotropic SHG response through the intrinsic polar order in 2D nonlinear optical crystals, opening a new paradigm toward the development of functional devices.

SEM Electron-Beam-Induced Ultrathin Carbon Deposition Layer on Cu Substrate: Improved Dry Oxidation Protection Performance than CVD Single Layer Graphene.

An amorphous carbon deposition layer (CDL) with nanoscale thickness induced by scanning electron microscope (SEM) electron beam is studied as a carbon-based protective layer on copper (Cu). CDL is prepared by inducing the deposition of pollutants or hydrocarbons in the cavity of SEM through electron beam irradiation (EBI). Wrinkles and cracks will not form and the interfacial spacing of CDL/Cu is smaller than Graphene/Cu (Gr/Cu). The thickness and coverage of the interfacial oxide layer of CDL/Cu are all smaller than that of the Gr/Cu after the same oxidation conditions. Characterization of Raman mapping also demonstrates that CDL shows better oxidation inhibition effects than graphene. The structure of CDL is determined to be C = C and C = O, CH3 - and C-O can be loaded vertically on CDL. Density functional theory (DFT) is employed for demonstrating the smaller interfacial gap of CDL/Cu, less wrinkles and cracks and larger adsorbing energy of water/oxygen compared with Gr/Cu. Molecular dynamic (MD) simulation also indicates that the diffusion of water or oxygen into CDL/Cu is more difficult and the oxidation of Cu covered by CDL is well suppressed. This work provides a new approach for the study of carbon-based antioxidant materials on Cu.

Ultrafast and Durable Sodium-Ion Storage of Pseudocapacitive VN@C Hybrid Nanorods from Metal-Organic Framework.

Vanadium nitride (VN) is a promising electrode material for sodium-ion storage due to its multivalent states and high electrical conductivity. However, its electrochemical performance has not been fully explored and the storage mechanism remains to be clarified up to date. Here, the possibility of VN/carbon hybrid nanorods synthesized from a metal-organic framework for ultrafast and durable sodium-ion storage is demonstrated. The VN/carbon electrode delivers a high specific capacity (352 mA h g-1), fast-charging capability (within 47.5 s), and ultralong cycling stability (10 000 cycles) for sodium-ion storage. In situ XRD characterization and density functional theory (DFT) calculations reveal that surface-redox reactions at vanadium sites are the dominant sodium-ion storage mechanism. An energy-power balanced hybrid capacitor device is verified by assembling the VN/carbon anode and active carbon cathode, and it shows a maximum energy density of 103 Wh kg-1 at a power density of 113 W kg-1.

Nanoscale characterization of the heterogeneous interfacial oxidation layer of graphene/Cu based on a SEM electron beam induced reduction effect.

Characterization of the interfacial oxidation layer of graphene/metal is a challenging task using conventional spectroscopy techniques because interfacial oxidation is heterogeneous at the nanoscale underneath the graphene. Here we developed a feasible method for nanoscale characterization of the interfacial oxidation layer of graphene/Cu (Gr/Cu) based on scanning electron microscopy (SEM) electron beam irradiation (EBI) induced reduction of interfacial oxides (SEM EBI-RIO method) at room temperature. The change in the thickness and coverage of the interfacial Cu oxide layer induced by EBI is responsible for the observed contrast reversal or change in SEM images of a targeted area with a width down to 200 nm in the EBI time scale of seconds to minutes. This method offers the capability of mapping heterogeneous interfacial oxidation of Gr/Cu with sub-100 nm spatial resolution and determining the range of thickness (1-5 nm) of the interfacial oxide layer. The SEM EBI-RIO method will be a powerful method to complement X-ray photoelectron spectroscopy (XPS), Raman microscopy, and high resolution transmission electron microscopy (HRTEM) for characterization of the interfacial oxidation layer of 2D materials and devices.

Divergent Carry-Over Effects of Hypoxia during the Early Development of Abalone.

After being exposed to environmental stimuli during early developmental stages, some organisms may gain or weaken physiological regulating abilities, which would have long-lasting effects on their performance. Environmental hypoxia events can have significant effects on marine organisms, but for breeding programs and other practical applications, it is important to further explore the long-term physiological effects of early hypoxia exposure in economically significant species. In this study, the Pacific abalone Haliotis discus hannai was exposed to moderate hypoxia (∼4 mg/L) from zygote to trochophora, and the assessments of hypoxia tolerance were conducted on the grow-out stage. The results revealed that juvenile abalones exposed to hypoxia at the early development stages were more hypoxia-tolerant but with slower weight growth, a phenomenon called the trade-off between growth and survival. These phenotypic effects driven by the hypoxia exposure were explained by strong selection of genes involved in signal transduction, autophagy, apoptosis, and hormone regulation. Moreover, long non-coding RNA regulation plays an important role modulating carry-over effects by controlling DNA replication and repair, signal transduction, myocardial activity, and hormone regulation. This study revealed that the ability to create favorable phenotypic differentiation through genetic selection and/or epigenetic regulation is important for the survival and development of aquatic animals in the face of rapidly changing environmental conditions.

Novel interrupted aortic arch: A case report.

BACKGROUND AND AIM OF THE STUDY: Interrupted aortic arch (IAA) is a rare and fatal malformation. Most patients with IAA are diagnosed in early childhood because of the severity of their symptoms. IAA is classified into three morphologic types (A, B, or C), depending on the site of the interruption. In our case, this patient did not have a common brachiocephalic trunk, left carotid artery, or left subclavian artery, IAA classification of this case cannot be judged based on the existing interruption method. METHODS: We present a 6-year-old Chinese boy with a history of neck masses since birth, and an echocardiogram from a local county hospital revealing an IAA without any cardiac anomalies, was referred to our hospital. RESULTS: The patient was feeling good and was nearly asymptomatic. Computed tomography angiography was performed, which indicated an absent aortic arch, likely due to disruption during development, and aortic discontinuity. The ascending aorta gave rise to both carotid arteries, and the descending aorta was supplied by large subclavian arteries. The right vertebral artery was supplied by right large collateral vessels that connected the right carotid artery. The left side was similar in structure to the right side. The descending aorta was supplied by large subclavian arteries. The subclavian arteries and carotid arteries were connected by large collateral vessels. Due to the large collateral vessels, the child's lower body had sufficient blood supplied, so that the typical differential cyanosis did not occur, and the child without symptomatic can survive to now. CONCLUSIONS: This patient did not have a common brachiocephalic trunk, left carotid artery, or left subclavian artery. Maybe, this patient belonged to a new type of IAA.

Transcriptome analysis reveals the molecular mechanisms of heterosis on thermal resistance in hybrid abalone.

BACKGROUND: Heterosis has been exploited for decades in different animals and crops due to it resulting in dramatic increases in yield and adaptability. Hybridization is a classical breeding method that can effectively improve the genetic characteristics of organisms through heterosis. Abalone has become an increasingly economically important aquaculture resource with high commercial value. However, due to changing climate, abalone is now facing serious threats of high temperature in summer. Interspecific hybrid abalone (Haliotis gigantea ♀ × H. discus hannai ♂, SD) has been cultured at large scale in southern China and has been shown high survival rates under heat stress in summer. Therefore, SD has become a good model material for heterosis research, but the molecular basis of heterosis remains elusive. RESULTS: Heterosis in thermal tolerance of SD was verified through Arrhenius break temperatures (ABT) of cardiac performance in this study. Then RNA-Sequencing was conducted to obtain gene expression patterns and alternative splicing events at control temperature (20 °C) and heat stress temperature (30 °C). A total of 356 (317 genes), 476 (435genes), and 876 (726 genes) significantly diverged alternative splicing events were identified in H. discus hannai (DD), H. gigantea (SS), and SD in response to heat stress, respectively. In the heat stress groups, 93.37% (20,512 of 21,969) of the expressed genes showed non-additive expression patterns, and over-dominance expression patterns of genes account for the highest proportion (40.15%). KEGG pathway enrichment analysis showed that the overlapping genes among common DEGs and NAGs were significantly enriched in protein processing in the endoplasmic reticulum, mitophagy, and NF-κB signaling pathway. In addition, we found that among these overlap genes, 39 genes had undergone alternative splicing events in SD. These pathways and genes may play an important role in the thermal resistance of hybrid abalone. CONCLUSION: More alternative splicing events and non-additive expressed genes were detected in hybrid under heat stress and this may contribute to its thermal heterosis. These results might provide clues as to how hybrid abalone has a better physiological regulation ability than its parents under heat stress, to increase our understanding of heterosis in abalone.

Air Bubble Bridge-Based Bioinspired Underwater Adhesion.

Wet adhesion is greatly demanded in fields of wearable devices, wound dressings, and smart robotics. However, reusable, noninvasive and convenient adhesive pads in the liquid environment have remained a challenge. Here, a novel concept of underwater adhesion inspired by the diving beetle, which utilizes the air bubbles as an adhesive to realize nondestructive and repeatable adhesion working across a wide range of scales is shown. The mechanism of underwater bubble adhesion is revealed by the capillarity of air-bubble bridge, of which the property depends on the dynamic bubble contact angles and the gap distance. The design principle of the air bubble-based underwater adhesion is proposed and validated to tune the interfacial acting force by theoretical and experimental results. Finally, a strong, reusable surface adhesive based on air bubble bridges is demonstrated from macro- to microscales in applications of particle manipulation and particle self-assembly. This unique view of underwater bubble adhesion provides new ideas for broader applications.

Ultrafast water harvesting and transport in hierarchical microchannels.

Various natural materials have hierarchical microscale and nanoscale structures that allow for directional water transport. Here we report an ultrafast water transport process in the surface of a Sarracenia trichome, whose transport velocity is about three orders of magnitude faster than those measured in cactus spine and spider silk. The high velocity of water transport is attributed to the unique hierarchical microchannel organization of the trichome. Two types of ribs with different height regularly distribute around the trichome cone, where two neighbouring high ribs form a large channel that contains 1-5 low ribs that define smaller base channels. This results in two successive but distinct modes of water transport. Initially, a rapid thin film of water is formed inside the base channels (Mode I), which is followed by ultrafast water sliding on top of that thin film (Mode II). This two-step ultrafast water transport mechanism is modelled and experimentally tested in bio-inspired microchannels, which demonstrates the potential of this hierarchal design for microfluidic applications.

High-Contrast SEM Imaging of Supported Few-Layer Graphene for Differentiating Distinct Layers and Resolving Fine Features: There is Plenty of Room at the Bottom.

For supported graphene, reliable differentiation and clear visualization of distinct graphene layers and fine features such as wrinkles are essential for revealing the structure-property relationships for graphene and graphene-based devices. Scanning electron microscopy (SEM) has been frequently used for this purpose where high-quality image contrast is critical. However, it is surprising that the effect of key imaging parameters on the image contrast has been seriously undermined by the graphene community. Here, superior image contrast of secondary electron (SE) images for few-layer graphene supported on SiC and SiO2 /Si is realized through simultaneously tuning two key parameters-acceleration voltage (Vacc ) and working distance (WD). The overlooked role of WD in characterizing graphene is highlighted and clearly demonstrated. A unified model of Vacc and WD dependence of three types of SE collected by the standard side-attached Everhart-Thornley (E-T) SE detector is conceptually developed for mechanistically understanding the improved mass thickness contrast for supported few-layer graphene. The findings reported here will have important implications for effective characterizations of atomically thick 2D materials and devices.

A nanostructured Fc(COCH3)2 film prepared using silica monolayer colloidal crystal templates and its electrochromic properties.

Since oxidation and reduction reactions mainly take place on surfaces, enlarging the specific surface of redox materials is the key to achieving excellent electrochemical performance. In this work, by using silica monolayer colloidal crystal templates (MCCTs), a nanostructured Fc(COCH3)2 film is prepared successfully, and such a nanostructure could exhibit the following unique electrochemical properties: the MCCTs could impede the aggregation tendency of Fc(COCH3)2 and possess high electrochemical activity; Fc(COCH3)2 enlarges the contact area and offers more active sites and faster electronic transmission channels. The structure, optical and electrochemical properties of the nanostructured Fc(COCH3)2 were tested and then compared with those of compact Fc(COCH3)2 films to evaluate the role of the nanoarchitecture. The unique structure design of the Fc(COCH3)2 film enables outstanding performance, showing a large transmittance change (ΔT) of 37% at 550 nm when switched between 0.5 V and -2.5 V, which is approximately ninefold higher than that of the compact Fc(COCH3)2 film (approximately 4%). Response times of coloration and bleaching are found to be only 16.15 s and 5.56 s. Furthermore, the nanostructured Fc(COCH3)2 film shows much better cycling stability than the compact one. The results indicate that the nanostructure could significantly improve the electrochemical performance of the Fc(COCH3)2 film due to the increase in electrochemical active sites and the enhancement of the "D-to-A" redox switch of ferrocene.

Relationship between asperity-mediated surface forces and topography alteration of silica microspheres sliding on mica, sapphire, and glass substrates under ambient conditions: atomic force microscopy and theoretical studies.

Contact geometry significantly influences adhesive force measurements and modeling for adhesion/friction studies where an AFM colloidal probe technique has been extensively employed. Here we present a systematic study on the topography alteration of silica microspheres sliding on mica, sapphire, and glass substrates under ambient conditions at a relative humidity of 30-55% and the consequential adhesion behaviors of worn microspheres through AFM direct force measurements and theoretical modeling. The wearing of microspheres creates a truncated platform, which is largest for sliding on glass substrates. On the platform are nanoasperities consisting of wear debris and airborne particulate contaminants. Variations in adhesive forces with sliding time and testing modes as well as the effect of surface roughness of substrates are explained within the theoretical framework of nanoasperity-mediated capillary and van der Waals forces. The drawbacks of the present reverse-imaging method for microsphere topography examination, and numerous sources of errors associated with the extraction of key parameters for force modeling, are discussed in detail. The results will also have important implications for more reliable AFM colloidal probe technique and its application in adhesion and tribological studies.

Mechanistic Insights into Plasma Oxidation of Ag Nanofilms: Experimental and Theoretical Studies.

Plasma oxidation of metals has been studied extensively to fabricate nanoporous oxides with the merits of room temperature treatment and facile control of the oxidation rate. Plasma oxidation of Ag, motivated by studies on atomic oxygen corrosion of Ag, is one of the most studied systems. However, several important questions remain unaddressed and even overlooked traditionally: the critical role played by atomic O in promoting oxidation, evolution of microstructures during plasma exposure, and a sound framework for quantitative oxidation kinetic analyses. In this paper, the O2 plasma oxidation behavior of Ag films deposited on Si substrates was systematically studied both experimentally and theoretically. The effects of plasma pressure and power on the microstructural evolution and oxidation kinetics of Ag films of various thicknesses were investigated using comprehensive characterization, as well as numerical analysis of plasma chemistry for deriving atomic O concentration. The findings here provide a full picture and deep mechanistic insights into the morphology and microstructure evolution of Ag films and the growth of dense or porous Ag2O and AgO oxide layers by plasma oxidation, revealing the intricate interplay between atomic O, vacancy creation, Ag ion diffusion, Kirkendall effect, formation of pores, and interfacial void coalescence. The methodology developed here can be easily transferred to help understand the plasma oxidation behavior of other metals.

Forward osmosis with a novel thin-film inorganic membrane.

Forward osmosis (FO) represents a new promising membrane technology for liquid separation driven by the osmotic pressure of aqueous solution. Organic polymeric FO membranes are subject to severe internal concentration polarization due to asymmetric membrane structure, and low stability due to inherent chemical composition. To address these limitations, this study focuses on the development of a new kind of thin-film inorganic (TFI) membrane made of microporous silica xerogels immobilized onto a stainless steel mesh (SSM) substrate. The FO performances of the TFI membrane were evaluated upon a lab-scale cell-type FO reactor using deionized water as feed solution and sodium chloride (NaCl) as draw solution. The results demonstrated that the TFI membrane could achieve transmembrane water flux of 60.3 L m(-2) h(-1) driven by 2.0 mol L(-1) NaCl draw solution at ambient temperature. Meanwhile, its specific solute flux, i.e. the solute flux normalized by the water flux (0.19 g L(-1)), was 58.7% lower than that obained for a commercial cellulose triacetate (CTA) membrane (0.46 g L(-1)). The quasi-symmetry thin-film microporous structure of the silica membrane is responsible for low-level internal concentration polarization, and thus enhanced water flux during FO process. Moreover, the TFI membrne demonstrated a substantially improved stability in terms of mechanical strength, and resistance to thermal and chemical stimulation. This study not only provides a new method for fabricating quasi-symmetry thin-film inorganic silica membrane, but also suggests an effective strategy using this alternative membrane to achieve improved FO performances for scale-up applications.

Enhancing anionic redox stability via oxygen coordination configurations.

Anionic redox in Li-rich cathode materials with disordered crystal structures has potential to increase battery energy density. However, capacity fading due to anionic redox-induced structural transformation hinders practical implementation. To address this challenge, it is crucial to understand the influence of the anion coordination structure on redox reversibility. By comprehensively studying the spinel-like Li1.7Mn1.6O3.7F0.3 and layered Li2MnO3 model systems, we found that tetrahedral oxygen exhibits higher kinetic and thermodynamic stability than octahedral oxygen in Li1.7Mn1.6O3.7F0.3 and Li2MnO3, effectively suppressing aggregation of oxidized anions. Electronic structure analysis showed that the 2p lone-pair states in tetrahedral oxygen lie deeper than those in octahedral oxygen. The Li-O-TM bond angle in a polyhedron is identified as a characteristic parameter to correlate anionic redox stability. TM substitutions using Co3+, Ti4+ and Mo5+ could effectively regulate the Li-O-Mn bond angle and anionic active electronic state. Our finding that anionic redox stability is influenced by the polyhedral structure offers new opportunities for designing high-energy-density Li-rich cathode materials.

High-Efficient Microdroplet Harvesting and Detaching Inspired from Sarracenia Lid Trichome.

Fog harvesting plays a pivotal role in harnessing atmospheric water resources and holds significant promise for alleviating global water scarcity. Nonetheless, enhancing harvesting efficiency remains a persistent challenge, especially concerning the rapid detachment of droplets from surfaces. In this study, we discovered that the trichomes of Sarracenia not only efficiently harvest and transport liquid but also quickly drain harvested liquid. We have elucidated the augmentation mechanism behind effective fog harvesting and drainage within the lid of Sarracenia. The trichomes facing the counterflow can enhance fog harvesting efficiency by 80% through air-flow-assisted spreading of liquid film. The wedge corner generated by the interface between hydrophilic and hydrophobic surfaces, coupled with the reduction of cross-sectional angles, diminishes the adhesive force of liquid droplets, fosters droplet spheroidization, and substantially facilitates droplet detachment. In addition, the quantitative detachment of droplets can be achieved by adjusting the cross-sectional angle and wetting gradient. This integrated structure combining efficient condensation and detachment has diverse applications in cooling towers and seawater desalination.

The study on the impact of sex on the structure of gut microbiota of bamboo rats in China.

Introduction: Bamboo rats are rodents that eat bamboo, and their robust capacity for bamboo digestion is directly correlated with their gut flora. Chinese bamboo rat (Rhizomys sinensis) is a common bamboo rat in Chinese central and southern regions. As a single-stomach mammal, bamboo rats are a famous specificity bamboo-eating animal and their intestinal microbial composition may also play a key role in the digestion of cellulose and lignin. So, the gut microbiota of bamboo rat may play an important role in the adaptation of bamboo rats for digesting lignocellulose-based diet. Methods: To study the microbiome differences of bamboo rats from different sexes, the microbial genomic DNA was extracted from each fecal sample and the V4 region of 16S rRNA genes was amplified and sequencing on an IlluminaHiSeq6000 platform. The operational taxonomic units (OTUs) were classified, the OTUs in different sexes was identified and compared at phylum and genus levels. For isolation and screening of cellulose degradation bacteria from bamboo rats, fresh feces from randomly selected bamboo rats were collected and used for the isolation and screening of cellulose degradation bacteria using Luria Bertani (LB) Agar medium containing Carboxymethyl cellulose. The cellulase activity, biochemical characterization and phylogenetic analysis of the purified bacteria strains were characterized. Results and discussion: A total of 3,833 OTUs were classified. The total microbial diversity detected in the female and male rats was 3,049 OTUs and 3,452 OTUs, respectively. The Shannon index revealed significant differences between the two groups (p < 0.05), though they were all captive and had the same feeding conditions. At the phylum level, Firmicutes, Bacteroidota, and Proteobacteria were prominent in the microbial community. At the genus level, the microbial community was dominated by Lachnospiraceae, Lactobacillus, Bacteroides, and Prevotella, but there was a significant difference between the two groups of bamboo rats; ~90 bacteria genus in the female group was significantly higher than the male group. Among them, Bacteroides, Colidextribacter, and Oscillibacter were significantly higher genera, and the genera of Lachnoclostridium, Oscillibacter, and Papillibacter had the highest FC value among the male and female bamboo rats. The KEGG function annotation and different pathways analysis revealed that membrane transport, carbohydrate metabolism, and amino acid metabolism were the most enriched metabolic pathways in the two groups, and multiple sugar transport system permease protein (K02025 and K02026), RNA polymerase sigma-70 factor (K03088), and ATP-binding cassette (K06147) were the three different KEGG pathways (p < 0.05). Two cellulose degradation bacteria strains-Bacillus subtilis and Enterococcus faecalis-were isolated and characterized from the feces of bamboo rats.

Metabolic and transcriptional responses demonstrating enhanced thermal tolerance in domesticated abalone.

Global warming threatens aquatic systems and organisms. Many studies have focused on the vulnerability and stress responses of aquaculture organisms to future thermal conditions. However, it may be of more practical significance to reveal their acclimation potential and mechanisms. In this study, the physiological, metabolic, and transcriptional responses to long-term temperature acclimation of northern and southern populations of Pacific abalone Haliotis discus hannai, a commercially important gastropod sensitive to environmental changes, were compared. This study conducted two common-garden experiments, including a thermostatic experiment in the lab and an aquaculture experiment on the farm. The abalone population cultured in warmer southern waters was tolerant of ongoing high temperatures, whereas the abalone population originally cultured in cooler northern waters exhibited vulnerability to high temperatures but could enhance its thermal tolerance through the process of natural selection in warmer southern waters. This difference was linked to divergence in the metabolic and transcriptional processes of the two populations. The tolerant population exhibited a greater capacity for carbohydrate and amino acid metabolism regulation and energy redistribution to cope with heat stress. This capacity may have been selected for, and accumulated, over many generations because the tolerant population originated from the intolerant population over two decades ago. This work provides insight into the vulnerability and acclimation potential of abalone to heat stress and discloses the molecular and metabolic traits underlying this phenomenon. Future research on the ability of abalone and other commercial shellfish species to acclimate to global warming should take this potential into account.

Secondary Metabolites from the Endoparasitic Nematophagous Fungus Harposporium anguillulae YMF 1.01751.

Harposporium anguillulae, an endoparasitic nematophagous fungus (ENF), is a model fungus from which the genus Harposporium was established. It can infect nematodes via ingested conidia. In this paper, the morphology and nematode-fungus interaction between Panagrellus redivivus and H. anguillulae were observed by scanning electron microscopy (SEM). The secondary metabolites of H. anguillulae were also studied. Seven metabolites were purified and identified from an ethyl acetate extract of broth and a methanol extract of mycelium. These include a new polyketone 5-hydroxy-3-(hydroxymethyl)-6-methyl-2H-pyran-2-one (1) and six known metabolites (17R)-17-methylincisterol (2), eburicol (3), ergosterol peroxide (4), terpendole C (5), (3ß,5α,9ß,22E)-3,5-dihydroxy-ergosta-7,22-dien-6-one (6), and 5α,6ß-epoxy-(22E,24R)-ergosta-8,22-diene- 3ß,7α-diol (7). These metabolites were assayed for their activity against plant root-knot nematode, Meloidogyne incognita, and the results showed that terpendole C (5) had weak nematicidal activity but also that other compounds did not have evident activity at a concentration of 400 µg mL-1. Compound 1 exhibited an attractive effect towards P. redivivus.

Origin of multiple voltage plateaus in P2-type sodium layered oxides.

Although layered transition metal (TM) oxides have attracted considerable attention for cathode materials of sodium-ion batteries, they suffer from uncontrolled multiple voltage plateaus due to local structure transformations such as TM-layer gliding and Na+/vacancy ordering upon Na+ extraction and insertion. However, the intrinsic origins of these local structure transformations are not fully understood, preventing the rational design of better cathode materials. Here, we concentrate on Na+/vacancy ordering in single phase domains to reveal the underlying mechanism of multiple voltage plateaus by tracking desodiation-induced electronic structure evolutions of two typical compounds, P2-Na0.6[Cr0.6Ti0.4]O2 and P2-NaCrO2. During desodiation, P2-NaCrO2 generates obvious multiple voltage plateaus, which are not observed in P2-Na0.6[Cr0.6Ti0.4]O2 due to TM disordering. A combination of first-principles desodiation calculations and electronic structure analysis reveals that charge localization accompanied by Na+ migration is an intrinsic feature of multiple voltage plateaus in P2-NaCrO2. A correlation between charge localization and multiple voltage plateaus is established by a comparative study in which P2-Na0.6[Cr0.6Ti0.4]O2 always follows the charge transfer order from high-activity to low-activity sites. This finding reveals that disordering design of active sites to avoid charge localization in redox is of much importance for developing high-performance Na-ion cathode materials.