Lead-free(Ba,Sr)TiO_(3)-based ceramics with superior tunable properties by the semi-solution method

High-performance dielectric tunable materials with both high dielectric tunability and low dielectric loss are urgently needed for new-generation electronic tunable devices.In the present study,a new system,(Ba_(0.675)Sr_(0.325))_(1−x)La_(x)Ti_(1−x)MnxO_(3)(x=0.25%,0.5%,0.75%,and 1.0%),was designed.The acceptor dopant Mn was added to lower dielectric loss,while the donor dopant La was introduced to enhance dielectric tunability.The samples were prepared using the conventional solid-state(CS)reaction method and the semi-solution(SS)method.The experimental results showed that the morphology of the ceramics was optimized by further improving the processing procedure.Dense microstructures,homogeneous grains,and uniform dopant distributions could be achieved successfully by the semi-solution method.Moreover,a significant enhancement in the tunable properties was realized owing to the improved microstructure mentioned above.The optimum tunable properties occurred in the samples prepared by the semi-solution method at x=0.75%,with a high dielectric tunability of 85.0%,a low dielectric loss of 0.0011,and an excellent figure of merit(FOM)of 773.The tunable properties of(Ba,Sr)TiO_(3)(BST)ceramics were even superior to those of lead-based materials,with an FOM of approximately 700.All the results suggested that the semi-solution method rendered BST ceramics more promising for applications in tunable devices.

Structural and dielectric tunable properties of Ba_(0.4)Sr_(0.6)Ti_(1-y)Si_yO_3 microwave ceramics

The structure-property relationships in Ba0.4Sr0.6Ti1-ySiyO3 with y=0.00,0.01,0.02,0.05,0.10 and 0.20 ceramics have been studied by using X-ray diffraction,electron microscopy and dielectric spectroscopy.An increase of Si concentration is not favorable for the stability of the perovskite structure,which results in the formation of BaTiSiO5 secondary phase.The dielectric peaks of samples are suppressed,broadened and shifted to low temperature with increasing Si concentration.Permittivity and Q value are reduced gradually with increasing Si concentration,due to growing of second BaTiSiO5 phase.The tunability(T) still remains ～18.0% under 60 kV/cm biasing for the samples with y-0.10.The best combination of microwave dielectric properties are obtained for the composition of y=0.10:-=531,Q=391(at 1.610 GHz) and T=17.7%.

Dynamic Crosslinked Phosphorescent Poly(vinyl alcohol)-Terpyridine Films with Enhanced Mechanical Properties and Tunable Shape Memory

Achieving versatile room temperature phosphorescence(RTP)materials,especially with tunable mechanical properties and shape memory is attractive and essential but rarely reported.Here,a strategy was reported to realize multi-functional RTP films with multicolor fluorescence,ultralong afterglow,adjustable mechanical properties,and shape memory through the synergistic dynamic interaction of lanthanide(Ln~Ⅲ)-terpyridine coordination,borate ester bonds,and hydrogen bondings in a poly(vinyl alcohol)(PVA)matrix.By varying the amount of borax,the mechanical properties of the films could be finely controlled due to the change of crosslinking degree of dynamic borate ester bonds in PVA.The assembly and disassembly of borate ester bonds upon the trigger of borax and acid were applied as reversible linkage to achieve programmable shape memory behavior.In addition,the films displayed both fascinating multicolor fluorescence and ultralong afterglow characteristics due to the presence of Ln III doping and confinement of terpyridine in PVA.This study provides a new avenue to impart modulable mechanical strength and shape memory to RTP materials.

Interlayer engineering in 3D graphene skeleton realizing tunable electronic properties at a highly controllable level for piezoresistive sensors

Three-dimensional(3D)graphene is a promising active component for various engineering fields,but its performance is limited by the hidebound electrical conductivity levels and hindered electrical transport.Here we present a novel approach based on interlayer engineering,in which graphene oxide(GO)nanosheets are covalently functionalized with varied molecular lengths of diamine molecules.This has led to the creation of an unprecedented class of 3D graphene with highly adjustable electronic properties.Theoretical calculations and experimental results demonstrate that ethylenediamine,with its small diameter acting as a molecular bridge for facilitating electron transport,has the potential to significantly improve the electrical conductivity of 3D graphene.In contrast,butylene diamine,with its larger diameter,has a reverse effect due to the enlarged spacing of the graphene interlayers,resulting in conductive degradation.More importantly,the moderate conductive level of 3D graphene can be achieved by combining the interlayer spacing expansion effect and theπ-electronic donor ability of aromatic amines.The resulting 3D graphene exhibits highly tunable electronic properties,which can be easily adjusted in a wide range of 2.56-6.61 S·cm^(-1)compared to pristine GO foam(4.20 S·cm^(-1)).This opens up new possibilities for its use as an active material in a piezoresistive sensor,as it offers remarkable monitoring abilities.

Facile intercalation of alkali ions in WO_(3)for modulated electronic and optical properties:Implications for artificial synapses and chromogenic application

Tungsten oxides(WO_(3))are widely recognized as multifunctional systems owing to the existence of rich polymorphs.These diverse phases exhibit distinct octahedra-tilting patterns,generating substantial tunnels that are ideally suited for iontronics.However,a quantitative comprehension regarding the impact of distinct phases on the kinetics of intercalated conducting ions remains lacking.Herein,we employ first-principles calculations to explore the spatial and orientational correlations of ion transport inγ-and h-WO_(3),shedding light on the relationship between diffusion barriers and the size of the conducting ions.Our findings reveal that different types and concentrations of alkali-metals induce distinct and continuous lattice distortions in WO_(3)polymorphs.Specifically,γ-WO_(3)is more appropriate to accommodate Li+ions,exhibiting a diffusion barrier and coefficient of 0.25 eV and 9.31×10^(-8)cm^(2)s^(-1),respectively.Conversely,h-WO_(3)features unidirectional and sizeable tunnels that facilitate the transport of K+ions with an even lower barrier and a high coefficient of 0.11 e V and 2.12×10^(-5)cm^(2)s^(-1),respectively.Furthermore,the introduction of alkali-metal into WO_(3)tunnels tends to introduce n-type conductivity by contributing s-electrons to the unoccupied W 5d states,resulting in enhanced conductivity and tunable electronic structures.These alkali metals in WO_(3)tunnels are prone to charge transfer,forming small polaronic states and modulating the light absorption in the visible and nearinfrared regions.These tunable electronic and optical properties,combined with the high diffusion coefficient,underscore the potential of WO_(3)in applications such as artificial synapses and chromogenic devices.

Fabrication of Cu_2O@Cu_2O core-shell nanoparticles and conversion to Cu_2O@Cu core-shell nanoparticles in solution

Cu2O@Cu2O core-shell nanoparticles (NPs) were prepared by using solution phase strategy. It was found that Cu2O@Cu2O NPs were easily converted to Cu2O@Cu NPs with the help of polyvinylpyrrolidine (PVP) and excessive ascorbic acid (AA) in air at room temperature, which was an interesting phenomenon. The features of the two kinds of NPs were characterized by XRD, TEM and extinction spectra. Cu2O@Cu NPs with different shell thicknesses showed wide tunable optical properties for the localized surface plasmon (LSP) in metallic Cu. But Cu2O@Cu2O NPs did not indicate this feature. FTIR results reveal that Cu+ ions on the surface of Cu2O shell coordinate with N and O atoms in PVP and are further reduced to metallic Cu by excessive AA and then form a nucleation site on the surface of Cu2O nanocrystalline. PVP binds onto different sites to proceed with the reduction utill all the Cu sources in Cu2O shell are completely assumed.

Chemically recyclable copolyesters from bio-renewable monomers:controlled synthesis and composition-dependent applicable properties

The development of chemically recyclable polymers is a promising solution to address the dual challenges of the environment and resources caused by petroleum-based plastics.Despite recent advancements,it is highly desirable for developing recyclable polymers to meet the requirements of both practical uses and well-performed recyclability.Bio-renewable monomers have been paid great attention recently as promising potential candidates for establishing a sustainable circular polymer economy.Herein,a sequential copolymerization of various bio-renewable n-alkyl substituted δ-valerolactone((R)VLs)and p-dioxanone(PDO)is conducted to synthesize novel chemically recyclable diblock copolymers poly(p-dioxanone)-block-poly(n-alkyl-valerolactones)(PPDO-b-P(R)VLs)with well-defined and controlled structures.The properties of copolymers including thermal property,crystallization,mechanical property,hydrophilicity and transport property can be tuned effectively to meet the requirements of practical uses by alternating the alkyl substituents(R)and the P(R)VLs content.In addition,the high-efficiency and facile chemical recycling of copolymers to PDO and(R)VL comonomers is realized with a high yield of>96.5%and a high purity of 99%.

Enhanced laser characteristics of pyrromethene 650 using modified PMMA as solid hosts

Solid-state samples based on modified polymethyl methacrylate （MPMMA） with methanol doped with the dye pyrromethene 650 （PM650） axe prepared. The effects of a volume percentage of methanol on the laser characteristics of the sample, including spectra properties, slope efficiency, photostability and tunable properties, are investigated. The broadband dye laser output wavelength is around 655 nm and a highest slope efficiency of 32.23% is achieved. Pumping the samples at a repetition rate of 5 Hz with a pulse energy of as high as 100 mJ （the fluence is 0.26 J/cm2）, the longest lifetime （168000 shots） is obtained in the sample （MMA：methanol=18：2）, and the corresponding normalized photostability reaches 109.19 GJ/mol. When the sample （MMA：methanol=18：2） is placed in a Shoshan-type oscilla- tor, the naxrow-linewidth operation is a continuous tuning range （up to 64 nm）. The results indicate that the laser characteristics of solid-state dyes can be greatly enhanced by using modified PMMA with methanol serving as the solid host.

Synthesis of high-purity silver nanorods with tunable plasmonic properties and sensor behavior

Through anisotropic Ag overgrowth on the surface of Au nanobipyramids(Au NBPs), high-purity and sizecontrolled Ag nanorods(Au/Ag NRs) are obtained by a simplified purification process. The diameters of the Au/Ag NRs are determined by the size of the as-prepared Au NBPs, and the lengths of the Au/Ag NRs are tunable using different amounts of Ag precursor in the growth solution. Surface-enhanced Raman scattering(SERS) studies using Rhodamine-6G(R6G) as a test molecule indicate that the Au/Ag NRs have excellent sensing potential. The tunable optical properties and strong electromagnetic effect of the Au/Ag NRs, along with their superior SERS signal enhancement, show that Au/Ag NRs are promising for further applications in plasmon sensing and biomolecular detection.

3D printed hydrogel for soft thermo-responsive smart window

Smart windows with tunable optical properties that respond to external environments are being developed to reduce energy consumption in buildings.In the present study,we introduce a new type of 3D printed hydrogel with amazing flexibility and stretchability(as large as 1500%),as well as tunable optical performance controlled by surrounding temperatures.The hydrogel on a PDMS substrate shows transparent-opaque transition with high solar modulation(ΔT_(sol))up to 79.332% around its lower critical solution temperature(L_(CST))while maintaining a high luminous transmittance(T_(lum))of 85.847% at 20℃.In addition,selective transparent-opaque transition above LCST can be achieved by patterned hydrogels which are precisely fabricated via a projection micro-stereolithography based 3D printing technique.Our hydrogel promises great potential applications for the next generation of soft smart windows.

Controlled synthesis and closed-loop chemical recycling of biodegradable copolymers with composition-dependent properties

The closed-loop recycling concept of the polymer wastes into building-block chemicals is attractive,but the closed-loop recycling of copolymers enabled by energy-efficient chemical recycling and cost-effective separations is still facing great challenges.Herein,for the first time,a one-pot sequential copolymerization of γ-butyrolactone(γ-BL) and p-dioxanone(PDO)using an economical ureas/alkoxides catalytic system is conducted to synthesize biodegradable and chemically recyclable poly-(γ-butyrolactone)-block-poly(p-dioxanone)(PγBL-b-PPDO) diblock copolymers with well-defined and controlled structures.The composition-dependent properties of PγBL-b-PPDO copolymers,including thermal properties and crystallization behavior,are investigated.The results show that the thermal stability and crystalline ability of PγBL are enhanced observably by introducing the PPDO block.Significantly,the PγBL-b-PPDO copolymers can be depolymerized efficiently into the corresponding co-monomers with a yield of over 95% by simply low-temperature pyrolysis under vacuum.Moreover,γ-BL and PDO monomers are selectively separated with an isolated purity of about 99% based on the difference in their physicochemical properties.Subsequently,their repolymerization is realized to obtain the copolymers with nearly identical structures and thermostability,demonstrating the closed-loop recycling of copolymers,i.e.,polymerization-depolymerization-repolymerization.This research provides important guidance for the design of novel sustainable polymers towards more efficient chemical recycling,separation and regeneration.

Tunable gold nanostar synthesis with surfactant-free system

Gold nanoparticle is an important photothermal conversion material in photothermal imaging and photothermal therapy research.There are diverse gold nanoparticles,including gold nanospheres,gold nanorods,gold nanocages,gold nanoshells and gold nanostars.Among them,gold nanostar(AuNS)possesses more excellent prospective imaging contrast agent for cancer diagnosis than other shapes of gold nanoparticles because of its larger photon interception area and cross section as well as scattering characteristics.The properties of AuNS are susceptible to synthetic methods and conditions.In this study,we presented surfactant-free methods to synthesize AuNS,discussed the relationship of AuNS characterization with the synthetic conditions and tested its photothermal effect.The results indicated that length and number of branches in AuNSs were the main factor for absorption wavelength in photothermal conversion,and the Au NSs could be more precisely controlled by changing the synthesis conditions.

Regulating the formation ability and mechanical properties of high-entropy transition metal carbides by carbon stoichiometry

Tremendous efforts have been dedicated to promote the formation ability of high-entropy transition metal carbides.However,the majority of methods for the synthesis of high-entropy transition metal carbides still face the challenges of high temperature,low efficiency,additional longtime post-treatment and uncontrollable properties.To cope with these challenges,high-entropy transition metal carbides with regulatable carbon stoichiometry(HE TMC)were designed and synthesized,achieving improved ability for single phase solid solutions formation,promoting of sintering and controllable mechanical properties.Two typical composition series,i.e.,easily synthesized(ZrHfTaNb)C(ZHTNC)and difficultly synthesized(Zr_(0.25)Hf_(0.25)Ta_(0.25)Ti_(0.25))C(ZHTTC)are selected to demonstrate the promoting formation ability of single phase solid solutions from carbon stoichiometry deviations.Single phase high-entropy ZHTTC,which has been proven difficult in forming a single phase solid solution,can be prepared with the decrease of C/TM ratio under 2000℃;while the high-entropy ZHTNC,which has been proven easy in forming a single phase solid solution,can be synthesized at lower temperatures with the decrease of C/TM ratio.The synergistic effect of entropy stabilization and reduced chemical bond strength gaining from carbon stoichiometry deviations is responsible for the formation of single phase solid solutions and the promoted sintering of HE TMC.For example,the relative density of bulk(ZrHfTaNb)C(SPS-ZHTNC)increases from 90.98%to 94.25%with decreasing the C/TM atomic ratio from 0.9 to 0.74.More importantly,the room temperature flexural strength,fracture toughness and brittleness index of SPS-ZHTNCcan be tuned in the range of 384 MPa–419 MPa,4.41 MPam–4.73 MPamand 3.679μm–4.083μm,respectively.Thus,the HE TMCprepared by adjusting the ratio of carbon to refractory transition metal oxides have great potential for achieving low temperature synthesis,promoted sintering and tunable properties.

Three-dimensional meta-architecture with programmable mechanical properties

Artificial metamaterials have attracted widespread attention of research communities due to their anomalous physical properties compared to those of conventional materials.In this study,we designed a three-dimensional(3D)lightweight metaarchitecture consisting of 6-connected anti-chiral honeycombs.The mechanical properties(e.g.Young’s modulus,compression strength,and Poisson’s ratio)of the proposed meta-architecture could be programmed by adjusting a series of geometric parameters,as shown through numerical simulations.Moreover,an optically sensitive polymer-based 3D meta-architecture with 6-connected anti-chiral features was constructed by the stereolithography method.Owing to the regulation of the negative Poisson’s ratio,3D meta-architecture achieved a greater ductility under compression than those of traditional truss structures while retaining a relatively high strength and low density.Compression experiments validated the excellent tunability of the mechanical properties of the proposed 3D 6-connected antichiral structure.The results suggest the promising applications of this structure in lightweight aircraft,vibration isolation,and mechanical sensors.

Recent advances in defined hydrogels in organoid research

Organoids are in vitro model systems that mimic the complexity of organs with multicellular structures and functions, which provide great potential for biomedical and tissue engineering. However, their current formation heavily relies on using complex animal-derived extracellular matrices (ECM), such as Matrigel. These matrices are often poorly defined in chemical components and exhibit limited tunability and reproducibility. Recently, the biochemical and biophysical properties of defined hydrogels can be precisely tuned, offering broader opportunities to support the development and maturation of organoids. In this review, the fundamental properties of ECM in vivo and critical strategies to design matrices for organoid culture are summarized. Two typically defined hydrogels derived from natural and synthetic polymers for their applicability to improve organoids formation are presented. The representative applications of incorporating organoids into defined hydrogels are highlighted. Finally, some challenges and future perspectives are also discussed in developing defined hydrogels and advanced technologies toward supporting organoid research.

Complementary doping of van der Waals materials through controlled intercalation for monolithically integrated electronics

Doping control has been a key challenge for electronic applications of van der Waals materials.Here,we demonstrate complementary doping of black phosphorus using controlled ionic intercalation to achieve monolithic building elements.We characterize the anisotropic electrical transport as a function of ion concentrations and report a widely tunable resistivity up to three orders of magnitude with characteristic concentration dependence corresponding to phase transitions during intercalation.As a further step,we develop both p-type and n-type field effect transistors as well as electrical diodes with high device stability and performance.In addition,enhanced charge mobility from 380 to 820 cm^2/(V·s)with the intercalation process is observed and explained as the suppressed neutral impurity scattering based on our ab initio calculations.Our study provides a unique approach to atomically control the electrical properties of van der Waals materials,and may open up new opportunities in developing advanced electronics and physics platforms.

Synthesis and characterization of poly(p-dioxanone)-based degradable copolymers with enhanced thermal and hydrolytic stabilities

Herein, we presented a novel biodegradable copolymer via the chain extending reaction of poly(pdioxanone)-co-poly(2-(2-hydroxyethoxy) benzoate)(PPDO-co-PDHB) prepolymer with hexamethylene diisocyanate(HDI) as a chain extender. The structures and molecular weight of PPDO-co-PDHB prepolymer and PPDO-co-PDHB-PU chain-extended copolymer are characterized via hydrogen nuclear magnetic resonance spectroscopy(1 H NMR) and viscosity test. The relationship between the molecular structures and properties of the chain-extended copolymers is established. The PPDO-co-PDHB-PU copolymers possess a better thermal stability comparing with the PPDO homopolymer. The study of mechanical properties shows that the elongation-at-break of PPDO-co-PDHB-PU is much higher than that of PPDO. The investigation of hydrolytic degradation behaviors indicates the degradation rate of PPDO can be controlled by adjusting the PDHB compositions, and proves that chain-extended copolymers exhibit an excellent hydrolytic stability being better than that of PPDO.

Record high photoresponse observed in CdS-black phosphorous van der Waals heterojunction photodiode

Two-dimensional(2D)materials have recently received great attention for their atomic thin thickness and thus derived outstanding electrical,optical and optoelectronic properties.Moreover,the dangling-bond-free surfaces of 2D materials enable the direct integration of different materials with various properties through van der Waals(vdW)forces into vdW heterostructures,providing new opportunities for constructing new type devices with superior performances.In this study,we report the vertical assembly of n-type CdS and p-type BP into p-n junctions.The electrically tunable heterojunction device shows a high current rectifying ratio up to8×103at a low bias voltage range of±1 V and an ideality factor of 1.5.More interestingly,the CdS/BP vdW heterojunction exhibits an ultra-high photoresponsivity up to 9.2×105A W-1and an ultra-high specific detectivity of 3.2×1013Jones with a low bias voltage of 1.0 V,which is among the highest in the reported results of 2D heterostructures.While operated at a self-powered mode,the device also exhibits excellent photodetection performances with a high photoresponsivity of0.27 A W-1and a high external quantum efficiency of 76%.Time-resolved photoresponse characterizations indicate that the device possesses a fast response time of about 10 ms.The developed CdS/BP vdW heterojunctions will find potential applications in the next-generation nanoscale electronics and optoelectronics applications.

A reversible acid-base fluorescent switch based on molecular cocrystal of 4-[2-4-quinolinyl)vinyl]phenol and tetrafluoroterephthalic acid

Photoactive cocrystal materials have received growing research interest in construction of photofunctional systems owing to the crucial roles in modifying the photo-related properties of molecular solids, based on the non-bonding interactions between self-assembly units. Herein, we report tunable luminescence and acid-base stimuli-responsive properties of a cocrystal assembled by 4-[2-(4-quinolinyl)vinyl]phenol (qv) and tetrafluoroterephthalic acid (a). The luminescent properties (such as wavelength, quantum yield and fluorescence lifetime) of qv.a changed obviously relative to the pristine qv, due to the proton transfer and the alternation of molecular arrangement within two-component crystalline material. The photoemission intensity of qv.a underwent from weak to strong upon HCl gas fuming, and the corresponding wavelength changed from 517 nm to 597 nm, which can be reversibly transferred after exposed in NH3. Such luminescent switching behavior may provide an effective way to develop new types of photoactive stimuli-responsive materials and optical sensors.