Ca2Nb3O10 Nanosheets Research Articles

Synergy of nitrogen dopants and cobalt single atoms in calcium niobate nanosheets for photocatalytic oxygen evolution

Abstract Successful separation of photoexcited charge carriers and their effective utilization are crucial for overcoming the slow kinetics of the four-electron process for photocatalytic oxygen evolution. Herein, a novel strategy utilizing urea as a source of N-doping on Ca2Nb3O10 nanosheets is adopted followed by the successful deposition of Co single atoms (Co-SAs) to achieve a synergistic effect. The presence of N-dopants and Co-SAs is validated via various experimental techniques. Besides, it is observed that the presence of N-doping contributed towards deposition of higher content of Co-SAs (0.21 wt%) in Ca2Nb3O10-xNx¬-CoSA nanosheets compared to 0.15 wt% for non-doped Ca2Nb3O10-CoSA. The optimized Ca2Nb3O10-xNx-CoSA nanosheets exhibited an impressive photocatalytic O2 evolution of ~727.22 µmol g-1 h-1 via the synergy of N-dopants and Co-SAs. As a result, O2 evolution response of Ca2Nb3O10-xNx-CoSA is 3.6 times higher than pristine Ca2Nb3O10 nanosheets (201.26 µmol g-1 h-1), 2.24 times better than Ca2Nb3O10-xNx nanosheets (323.42 µmol g-1 h-1), and 1.77 times higher compared to Ca2Nb3O10-CoSA, (409.33 µmol g-1 h-1), clearly demonstrated the synergistic effect of N-dopants and Co-SAs in Ca2Nb3O10-xNx-CoSA nanosheets. Base on the finding of various characterization techniques, the co-presence of N-dopants and Co-SAs is observed to contribute towards better charge carriers separation, and utilization to achieve superior photocatalytic response. Thus, this work presents a novel approach for incorporating N-dopants and Co-SAs on Ca2Nb3O10 nanosheets which can be extended to wide range of nanosheets produced by the soft chemical exfoliation method.

Largely enhanced high‐temperature energy storage performance of P(VDF‐HFP) dielectric films via calcium niobate nanosheets

AbstractThe capacitive energy‐storage capacity of most emerging devices rapidly diminishes with increasing temperature, making high‐temperature dielectrics particularly desirable in modern electronic systems. In this work, calcium niobate (Ca2Nb3O10, CNO) nanosheets have been added into poly(vinylidene fluoride‐hexafluoropropylene) (P(VDF‐HFP), PVHP), forming PVHP/CNO nanocomposites with exceptional temperature stability and ultrahigh energy storage density. Especially, at 80°C and 450 MV/m, the PVHP/0.3 wt%CNO nanocomposite shows an excellent Wrec of 10.81 J/cm3 which is higher than previous PVDF‐based composite films at high temperatures. Because of the high dielectric permittivity of CNO nanosheets and the way that the parallel organization of the nanosheets blocks the course of electrical trees, nanocomposites exhibit greater dielectric constants and breakdown field strengths simultaneously. These findings, will be helpful in the development of flexible, high‐energy‐density capacitors that have stable performance at high temperatures.Highlights A record‐high high‐temperature Wrec is obtained. Excellent temperature stability from 25 to 80°C is achieved. The incorporation of Ca2Nb3O10 nanosheets significantly enhances Eb.

2D perovskite Ca2Nb3O10 nanosheet featuring Berry curvature dipole and canted persistent spin texture reversible with in-plane ferroelectricity

Two-dimensional materials can result in rich and unique electronic features through symmetry breaking. A wide band gap 2D perovskite Ca2Nb3O10 (CNO) nanosheet is investigated for exotic electronic or spin-related properties using state-of-the-art first-principles calculations. The CNO nanosheet exhibits spontaneous in-plane ferroelectric polarization confined in the y direction owing to the low symmetry of the crystal structure. A canted persistent spin texture (PST) can be observed in spin-split bands, which depict a unidirectional spin configuration tilted along the yz-plane. A correlation between the canted PST and ferroelectricity has been found, as in-plane ferroelectric switching can successfully reverse the typical PST. The nonvanishing Berry curvature dipole (BCD) resulting from the interplay of spin–orbit coupling (SOC) and inversion symmetry breaking is also reversible with in-plane ferroelectric polarization. Therefore, the possibility of fully electrically adjustable canted PST and BCD in a 2D perovskite CNO nanosheet provides a pathway toward creating affordable, non-volatile spintronic devices.

Identifying ultrathin dielectric nanosheets induced interface polarization for high-performance solid-state lithium metal batteries

Solid-state lithium metal batteries (SSLMBs) with polymer electrolytes are promising due to enhanced safety and high energy density, but the low ionic conductivity of polymer electrolytes and the unstable interface of lithium metal anode hinder the development of SSLMBs. Herein, we propose a unique strategy to address these challenges by coupling ultrathin high-dielectricity Ca2Nb3O10 (CNO) nanosheets with PEO-based electrolyte. The interfacial polarization originating from the distortion of NbO6 octahedra along the vertical direction of CNO nanosheets is maximized and so the interaction between CNO and LiTFSI, which greatly supports the dissociation of LiTFSI and improves the ionic conductivity (2.0 × 10−4 S cm−1) of the composite polymer electrolyte, compared to that without CNO. The optimized interfacial polarization effect is thoroughly demonstrated by theoretical calculation and experimental results. Moreover, due to a homogeneous, robust and LiF-rich solid electrolyte interphase film with promoted Li ion transport being formed at the lithium metal interface, the superior cycling stability (90 % capacity retention after 440 cycles at 0.5 C) and rate capability for LFP||Li full batteries are achieved. This design of composite polymer electrolyte with ultrathin dielectric nanosheet fillers demonstrates a new approach to the development of high-performance polymer electrolytes for SSLMBs.

2D Ca2Nb3O10 Optoelectronic Neuromorphic Device for Ultrasensitive UV‐C Vision and Encrypted Communication

AbstractNeuromorphic device that percepts ultraviolet (UV) radiations is essential for supplementing human visual perception. However, UV‐responsive synapses with high sensitivity and wavelength selectivity have not yet been developed so far. Herein, 2D optoelectronic synapses that are able to distinguish between UV‐A, UV‐,B and UV‐C radiations using a single material are demonstrated. The synapses use Ca2Nb3O10 nanosheets with wide bandgap and persistent photoconductivity effect (PPC) as UV‐responsive layer. The devices can detect UV‐C rays at ultralow intensity of 70 nW cm−2, which is the lowest record among 2D UV synaptic devices. Moreover, such a device demonstrates UV image vision, recognition, and memorization functions based on its diverse synaptic behaviors. The atomically thin UV synapses provide implications for enhancing human visual perception capabilities with spectral selectivity, ultrahigh sensitivity, and low‐energy consumption.

Using a perovskite oxide buffer layer on Ca2Nb3O10 nanosheets for the epitaxial growth of Pb(Zr0.52Ti0.48)O3 for electrode-free thin films

Ca2Nb3O10 nanosheet layers were deposited on Gallium Nitride (GaN)-on-Si substrates by the Langmuir-Blodgett method to obtain (001)-oriented growth of perovskite oxide thin films using pulsed laser deposition. We investigated the influence of 10 nm thick SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) and LaMnO3 films as buffer layers on the structural and ferroelectric properties of subsequentially grown Pb(Zr0.52Ti0.48)O3 (PZT) films, which may be used as gate capacitors in high power GaN devices. Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray-Diffraction and in-plane polarization experiments were used to determine the influence of the oxide buffer layers on the PZT properties. Highly crystalline dense (001)-oriented PZT films with large in-plane polarizations were obtained using SrTiO3 and LSAT as buffer layers. For SrTiO3 and LSAT we observed an improvement of the structural and ferroelectric properties compared to PZT grown directly on the Ca2Nb3O10 nanosheets and or using a LaMnO3 buffer layer. The improved high-crystallinity PZT films grown on GaN using ultrathin buffer layers could enhance the performance of high-power semiconductor electronics or in other devices where there is a need for a ferroelectric layer without bottom electrode.

BiFeO3-Based All Perovskite Oxides Direct Z-Scheme Heterostructure for Efficient Oxygen Evolution

BiFeO3 (BFO) has gained significant attention recently in photocatalytic water splitting due to its visible light active profile and facile synthesis design. However, a single component photocatalyst usually suffers from significant photoexcited charge-carrier recombination. To overcome this problem, BFO nanocuboids are coupled with two-dimensional Ca2Nb3O10 (CNO) nanosheets via a facile electrostatic self-assembly method. The surface charge of BFO nanocuboids is modulated via deposition of Co-nanoparticles to obtained positively charged BFO-Co nanocuboids. Resultantly, the combination of positively charged BFO-Co nanocuboids and negative charged CNO nanosheets demonstrated a direct Z-scheme heterojunction. The optimized BFO-Co/CNO heterostructure achieved outstanding photocatalytic O2 evolution (48.19 mmol g–1), which is 6.72 times higher than pristine BFO (7.17 mmol h–1 g–1). Different characterization confirmed that BFO-Co/CNO heterostructures exhibited improved charge-carrier separation and utilization compared to individual components. This improved response can be associated with a better contact interface between the oppositely charged surfaces with the added advantage of the perovskite nature of both components. As a result, BFO-Co/CNO heterostructures achieved the highest O2 evolution response for BFO-based heterostructures to date. This study offers a novel strategy for modulating the BFO nanocuboids surface charge via Co-nanoparticles deposition, which concomitantly worked as a cocatalyst, a potential strategy that can be applied for the design of various heterostructures.

Combined structural analysis and cathodoluminescence investigations of single Pr3+-doped Ca2Nb3O10 nanosheets

Due to the novel properties of both 2D materials and rare-earth elements, developing 2D rare-earth nanomaterials has a growing interest in research. To produce the most efficient rare-earth nanosheets, it is essential to find out the correlation between chemical composition, atomic structure and luminescent properties of individual sheets. In this study, 2D nanosheets exfoliated from Pr3+-doped KCa2Nb3O10 particles with different Pr concentrations were investigated. Energy dispersive X-ray spectroscopy analysis indicates that the nanosheets contain Ca, Nb and O and a varying Pr content between 0.9 and 1.8 at%. K was completely removed after exfoliation. The crystal structure is monoclinic as in the bulk. The thinnest nanosheets are 3 nm corresponding to one triple perovskite-type layer with Nb on the B sites and Ca on the A sites, surrounded by charge compensating TBA+ molecules. Thicker nanosheets of 12 nm thickness (and above) were observed too by transmission electron microscopy with the same chemical composition. This indicates that several perovskite-type triple layers remain stacked similar to the bulk. Luminescent properties of individual 2D nanosheets were studied using a cathodoluminescence spectrometer revealing additional transitions in the visible region in comparison to the spectra of different bulk phases.

Composite design of two-dimensional inorganic nanosheets for flexible energy storage capacitors

We present a new approach for designing flexible energy storage capacitors using two-dimensional (2D) inorganic nanosheets. 2D dielectric Ca2Nb3O10 nanosheet and ferroelectric poly(vinylidene fluoride) (PVDF) were selected as model material systems. Langmuir–Blodgett deposition was utilized for layer-by-layer engineering of (Ca2Nb3O10/PVDF) nanocomposite films on an indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrate. Such a new composite design realized the simultaneous improvement of energy density (∼7 J cm−3) and efficiency (∼78 %) even in the ultrathin form (∼20 nm) on the ITO-coated PET substrate. Nanosheet-based flexible capacitors also maintained a stable performance even after 104 times bending cycles. These results indicate that our nanosheet approach is of technological importance for exploring new flexible dielectric capacitors.

Impact of two-step calcination on microstructure, phase, electronic, and dielectric properties of KCa2Nb3O10 bulk layered perovskite

ABSTRACT The effects of varying calcination temperature, K content, and the number of calcination steps in the dielectric performance of KCa2Nb3O10 synthesized via solid-state reaction are investigated. Adding an extra calcination step at 500°C followed by another calcination at 1100°C suppressed the formation of secondary phases while maximizing the relative density (95%) and the average grain area (2.12 μm2). The first calcination at 500°C ensures the formation of intermediate phases (KNbO3 and Ca2Nb2O7), which are prerequisites for single-phase KCa2Nb3O10 synthesis. A significantly high dielectric constant of 352 at 100k Hz is achieved in the two-step calcined sample despite the low sintering temperature of 1250°C. The highest resistivity of the two-step calcined sample (2 × 108 Ω cm) obtained from complex impedance analysis supports its lowest dielectric loss (0.034 at 100k Hz). When the two-step calcined KCa2Nb3O10 powder is exfoliated, much higher dielectric properties of Ca2Nb3O10 nanosheets are expected.

Investigation on tunable ferroelectricity of polymer-based composites via changing the surface state of ferroelectric nanosheets

Polymer-based materials play a crucial role in progressive electronic devices and electric power systems due to their excellent ferroelectric and dielectric performances. High ferroelectricity of the polymers could be achieved even at a low electric field with ferroelectric nanofillers introduced. However, the origin of the extra ferroelectricity enhancements of these composites besides the intrinsic ferroelectricity of fillers are still ambiguous. Herein, the Ca2Nb3O10 (CNO) nanosheets were selected as ferroelectric nanofillers, which were embedded into the polyvinylidene fluoride (PVDF)-based polymer matrix. Numerous characterization results manifested that the surface of ferroelectric nanofillers could induce the formation of polar-oriented amorphous fractions (OAFs) in the composites. Experimental results indicated these formed OAFs are the origination of the enhanced ferroelectricity of the composites. In contrast, the aluminum oxide layer was constructed onto the CNO surface to cut off the interaction between the CNO nanosheets and the polymer matrix. These effects could be eliminated when the direct contact between the nanofiller and polymer matrix is interrupted, which facilitates the energy storage performance enhancements of the composites. This work reveals the origin of the extra ferroelectricity enhancements of polymer-based composites containing ferroelectric nanofillers. It may blaze new trails in realizing multifunctional applications of polymer-based composites via surface engineering.

Orientation control of Platinum electrode grown on silicon using [Ca2Nb3O10]− nanosheets as seed layer.

Platinum (Pt) is a noble metal with low resistivity and resilience to oxidation, which is largely used in microelectronic devices. In order to facilitate the integration of Pt thin films on silicon substrate, we are showing the ability to control their orientation by using [Ca2Nb3O10]− nanosheets (CNOns) as seed layer. Pt thin films were sputtered on silicon coated by CNOns (CNOns/SiO2/Si), and on TiO2/SiO2/Si substrates for comparison, at temperatures ranging from room temperature up to 625°C. Under pure argon, highly (111) textured Pt thin films were obtained on both substrates, regardless of the deposition temperature. However, by using an oxygen/argon mixture, highly (200) textured films could be obtained, only on CNOns/SiO2/Si substrate, when the substrate temperature is above 550°C. X-ray diffraction, scanning electron microscopy, and atomic force microscopy were used to characterize the crystalline quality, thickness, surface morphology and roughness of the Pt thin films. Their resistivity was measured at room temperature by the four-point probes method.

Integration of filter membrane and Ca2Nb3O10 nanosheets for high performance flexible UV photodetectors

• We first report the integration of filter membrane and Ca 2 Nb 3 O 10 nanosheets UV photodetectors (FM@CNO UV PDs). • The FM@CNO PD shows high responsivity (0.08 AW −1 ), high detectivity (1.1 × 10 12 Jones), high UV/visible rejection ratio (3.86 × 10 3 ) and fast speed (0.12/1.24 ms) under 300 nm light illumination. • The FM@CNO PD exhibits excellent flexibility after many bending cycles. And the FM@CNO array device can be used as a pixel array detector for UV imaging. We report that the integration of filter membrane and Ca 2 Nb 3 O 10 nanosheets (FM@CNO) UV photodetector (UV PD) shows high performance and excellent flexibility. The Ca 2 Nb 3 O 10 nanosheets were prepared by a facile solid-state reaction and liquid exfoliation process. The Ca 2 Nb 3 O 10 nanosheets can be integrated into the pores of a filter membrane via a simple vacuum filtration method. The FM@CNO UV PD shows high performance under 300 nm light illumination at 5 V bias, including high responsivity (0.08 AW −1 ), high detectivity (1.1 × 10 12 Jones), high UV/visible rejection ratio (3.86 × 10 3 ) and fast speed (0.12/1.24 ms). Furthermore, the FM@CNO device exhibits excellent flexibility after many bending cycles. In addition, the FM@CNO array device was used as a pixel array detector for UV imaging. This work provides a novel approach to achieve high performance flexible PDs based on filter membrane and two dimensional materials.

Greatly enhanced energy density in polymer nanocomposites coated with high-k perovskite nanosheets

Polymer dielectric materials with high energy storage density are vital component in advanced electronic devices. However, the increase of conduction loss at relatively high electric field will lead to film failure and hinder the exploration of high energy density in the dielectric polymer. Herein, a general strategy is proposed to effectively enhance the breakdown strength and energy density by coating wide bandgap Ca2Nb3O10 nanosheets on the surface of the polyvinylidene fluoride film using Langmuir-Blodgett and spray coating technologies. The coating layers of Ca2Nb3O10 nanosheets exhibit high insulation feature, and therefore, suppress the leakage current density of the nanocomposite film, resulting in remarkably enhanced breakdown strength of 710 MV/m and discharged energy density of 25.1 J/cm3, with a satisfactory charge–discharge efficiency of 78%. Our work may provide a scalable, and yet effective route to tailor the energy storage density of polyvinylidene fluoride-based polymers.

Improved Energy Storage Performance of PVDF Nanocapacitors by Utilizing 2D Inorganic Barrier Layers

We demonstrated a rational approach for designing high-performance polymer-based energy storage capacitors. Two-dimensional paraelectric Ca2Nb3O10 nanosheets were deposited on a ferroelectric poly(vinylidene fluoride) (PVDF) film to form paraelectric/ferroelectric hetero-assemblies. Such an artificial structuring enabled tailoring of the breakdown strength and dielectric response, realizing an enhanced energy density (~10 J cm−3) compared to pristine PVDF film (~ 1 J cm−3).

Constructing bidirectional-matched interface between polymer and 2D nanosheets for enhancing energy storage performance of the composites

Interfacial engineering, specifically core-shell architecture with highly insulating inorganic shell layer is generally adopted to improve the energy storage density (Ue) of polymer composites. However, the amorphous inorganic shell layer seems to be the only choice, as substantial interfacial tension arose from the core-shell lattice mismatch. Especially for the 2D nanosheets with high aspect ratio and highly crystallized surface, free volume between interfacial region is inevitably formed, restricting further Ue improvements of polymers. Here, bidirectional matched (bm) aluminum oxide interface transition regions are constructed between polyimide (PI) and Ca2Nb3O10 (CNO) nanosheets to prepare the composites (PI/CNO@AO). The bm-interface includes the inner core-shell lattice matched region and the outer shell-matrix structure matched region, and the gradual transition between them has been confirmed. Numerous experimental and characterization results manifested the successful construction of the bm-interface, and the interface could intrinsically depress the carrier transportation and electric conduction of the composites. Meanwhile, the simulated electric breakdown paths evolution in the PI/CNO@AO composites further confirms the results. Consequently, excellent energy storage performance of the composites is obtained at both conventional and high-temperature environments. The bm-interface design strategy holds great promises and may blaze new trails in preparing high energy density polymer dielectric capacitors.

Correlated Metals Transparent Conductors with High UV to Visible Transparency on Amorphous Substrates

AbstractCorrelated metals with high carrier density and strongly correlated electron effects provide an alternative route to achieve transparent conducting materials, different from the conventional degenerately doped wide‐bandgap transparent conducting oxides (TCO). The extremely low electrical resistivity and high optical transparency in the ultraviolet‐visible spectral range shown in 4d correlated metals present an advantage over conventional TCOs. However, most of the 4d correlated metals are grown epitaxially on single crystal substrates. Here, it has been shown that Ca2Nb3O10 nanosheets with different buffer layers promote the growth of high‐quality 4d2 SrMoO3 films on fused silica substrates, overcoming the use of expensive and size‐limited single‐crystal substrates. The room temperature electrical resistivity of SrMoO3 is as low as 61 µΩ cm, the lowest reported value on amorphous transparent substrates to date, without compromising its high optical transmittance. 4d1 correlated metal SrNbO3 on Ca2Nb3O10 nanosheets also exhibits similarly high optical transmittance but a higher room temperature resistivity of 174 µΩ cm. These findings facilitate the use of highly conducting and transparent 4d correlated metals not only as TCOs on technologically relevant substrates for the applications in the ultraviolet‐visible spectral range but also as electrodes for other oxide‐based thin film technologies.

Solution-Processed Two-Dimensional Metal Oxide Anticorrosion Nanocoating.

Molecularly thin two-dimensional (2D) nanomaterials are attractive building blocks for constructing anticorrosion nanocoatings as an ultimate pursuit in the metal-related industry. However, the nanocoating of prefocused graphene is far from industrial demands due to its high cost, low scalability, and insufficient quality. We propose all requirements to realize rational anticorrosion nanocoating of metal oxide nanosheets. The proof-of-concept study with Ti0.87O2 and Ca2Nb3O10 nanosheets demonstrates that the 10 and 20 nm thick coatings fabricated by a facile layer-by-layer (LbL) self-assembly on stainless steel (SUS) give perfect inhibition efficiency (IE) values of 99.92% and 99.89%, respectively. A driving test with a nanosheet-coated car-baffle demonstrated suitable corrosion resistance and mechanical and thermal robustness for industrial applications. The revealed and controlled thermal oxidation mechanisms are critical toward high-temperature application of the 2D oxide anticorrosion nanocoating. The advantages of nanosheet coating and extensible materials design will open a solid but exciting route to anticorrosion nanotechnology.

High-Performance Two-Dimensional Perovskite Ca2Nb3O10 UV Photodetectors.

We first report two-dimensional (2D) perovskite Ca2Nb3O10 ultraviolet photodetectors (UV PDs), which are prepared via a facile calcination-exfoliation method. The 2D Ca2Nb3O10 PDs demonstrate high performance at 3 V at 280 nm, high responsivity (14.94 A W-1), high detectivity (8.7 × 1013 Jones), high spectral selectivity (R280/R400 = 8.84 × 103), fast speed (0.08/5.6 ms), and long-term stability, exceeding those of most reported UV PDs. Furthermore, the Ca2Nb3O10 PDs integrated with poly(ethylene terephthalate) (PET) show excellent flexibility and have high linear dynamic range (96 dB). Our work provides a general strategy for searching new UV PDs based on numerous layered niobates. The Ca2Nb3O10 nanosheets may be one of the optimum semiconductor materials for next-generation high-performance UV PDs.

Integration of Single Oriented Oxide Superlattices on Silicon Using Various Template Techniques.

To benefit from the diverse functionalities of perovskite oxides in silicon-based complementary metal oxide semiconductor (CMOS) technology, integrating oxides into a silicon platform has become one of the major tasks for oxide research. Using the deposition of LaMnO3/SrTiO3 (STO) superlattices (SLs) as a case study, we demonstrate that (001) single oriented oxide SLs can be integrated on Si using various template techniques, including a single-layer buffer of STO prepared by molecular beam epitaxy (MBE) and pulsed laser deposition, a multilayer buffer of Y-stabilized zirconia/CeO2/LaNiO3/STO, and STO-coated two-dimensional nanosheets of Ca2Nb3O10 (CNO) and reduced graphene oxide. The textured SL grown on STO-coated CNO nanosheets shows the highest crystallinity, owing to the small lattice mismatch between CNO and STO as well as less clamping from a Si substrate. The epitaxial SL grown on STO buffer prepared by MBE suffers the largest thermal strain, giving rise to a strongly suppressed saturation magnetization but an enhanced coercive field, as compared to the reference SL grown on an STO single crystal. These optional template techniques used for integrating oxides on Si are of significance to fulfill practical applications of oxide films in different fields.