Artificial solid electrolyte interface layer based on sodium titanate hollow microspheres assembled by nanotubes to stabilize zinc metal electrodes

Recently,aqueous zinc-ion batteries with intrinsic safety,low cost,and environmental benignity have attracted tremendous research interest.However,zinc dendrites,harmful side reactions,and zinc metal corrosion stand in the way.Herein,we use lepidocrocite-type sodium titanate hollow microspheres assembled by nanotubes to constitute an artificial solid electrolyte interface layer on the zinc metal electrode.Thanks to the hierarchical structure with abundant open voids,negative-charged layered framework,low hydrophilicity,electrically insulting nature,and large ionic conductivity,the sodium titanate coating layer can effectively homogenize the electric field,promote the Zn^(2+)ion transfer,guide the Zn^(2+)ion flux,reduce the desolvation barrier,improve the exchange current density,and accommodate the plated zinc metal.Consequently,this coating layer can effectively suppress zinc dendrites and other unfavorable effects.With this coating layer,the Zn//Zn symmetric cell is able to provide an impressive cumulative zinc plating capacity of 1375 m Ah cm^(-2) at a current density of 5 m A cm^(-2).This coating layer also contributes to significantly improved electrochemical performances of Zn//MnO_(2) battery and zincion hybrid capacitor.This work offers new insights into the modifications of zinc metal electrodes.

Synergistic effects of CdS in sodium titanate based nanostructures for hydrogen evolution

In this paper, nanotubes and nanoribbons of sodium titanate structures were synthesized via hydrothermal methods in alkaline solution. CdS decorated titanate nanotubes and nanoribbons were therefore constructed for exploring the performance of hydrogen evolution and synergistic effect of CdS based titanate structures. CdS decorated titanate nanotubes and nanoribbons were characterized by high resolution transmission electron microscopy （HRTEM）, X-ray diffraction （XRD）, UV-vis, Brunauer- Emmett-Teller （BET） and X-ray photoelectron spectroscopy （XPS） measurements. CdS encapsuled in titanate nanotubes （CdS-ETNTs） showed the best capacity of H2 evolution by water splitting and stability than that from the other two structures, i.e., CdS doped titanate nanotubes （CdS-DTNTs） and CdS doped titanate nanoribbons （CdS-DTNRs）, which could be explained by the synergistic effect of decorated CdS with sodium titanate structures and confinement effect of CdS nanoparticles encapsuled inside

Sodium Titanate/Carbon （Na2Ti3O7/C） Nanofibers via Electrospinning Technique as the Anode of Sodium-ion Batteries

To overcome the sluggish kinetics in sodium-ion batteries, sodium titanate/carbon （Na2Ti3O7/C） composite nanofibers as anode materials have successfully been synthesized via a simple electrospinning method. After calcination at 800 ℃ for 3 h, the obtained Na2Ti3O7 nanoparticles are randomly dispersed in the matrix of in situ pyrolized carbon nanofiber. The Na2Ti3O7/C hybrid nanofiber obtained with 2.5 wt% ofpoly （vinylpyrrolidone） additive in the precursor solution has the smallest diameter of-120 nm and the finest particle size of -40 nm, exhibiting the best rate performance of 101 mAh.g-1 at 4 C and excellent capacity retention of 82% at 1 C after 100 cycles. Furthermore, this composite nanofiber also demonstrates good cycling performance under low current density of 0.1 C, which is attributed to the formation of stable solid electrolyte interface （SEI） film induced by small volume expansion/contraction of the fine NazTi3O7 nanoparticles during the charge/discharge process.

Oxygen vacancy migration and its lattice structural origin in A-site non-stoichiometric bismuth sodium titanate perovskites

Off-stoichiometry of perovskite structural Bi0.5Na0.5TiO3(BNT)ferroelectrics can give rise to considerable oxide-ion conductivity.The inherent structural characteristics are urgent to be resolved due to its particular sensitivity of the conduction mechanism to the nominal composition and synthesis process.Herein,a thorough study of the temperature-dependent neutron,X-ray diffraction and Raman spectrum is carried out on a series of equivalently substituted A-site deficient non-stoichiometric and pristine BNT.Phase transition and defect association are systemically investigated in these dominated rhombohedral phases at room temperature,associated with well saturated ferroelectric states.Significant structural evolution identified by Rietveld refinements and the origin of the electrical performance are clarified at elevated temperatures,focusing on the subtle distortions of ionic displacements,oxygen octahedral tilts and local chemical environments for oxygen vacancies.The ion migration ability mediated by oxygen vacancies that are not energetically favorable in BNT mainly depends on the external substitutional disorder,and is strongly affected by the dopant concentration.Together with the lone pair substitution concept,superior oxide ionic conductivity is achieved,and an alternative strategy is provided in designing BNT based oxide ion conductors.

Orientation dependence on piezoresponse of lead-free piezoelectric sodium bismuth titanate epitaxial thin films

Lead-free piezoelectric sodium bismuth titanate((Bi0.5Na0.5)TiO3,BNT)thin films were epitaxially grown onto(001)-,(110)-,and(111)-oriented Nb:SrTiO3(STO)single crystal substrates prepared by sol-gel processing.Highly oriented growth in(001),(110),and(111)BNT thin films was obtained in this work benefiting from the lattice match between the BNT film and the STO substrate.The different growth models in thin films with various orientations result in various surface morphologies dependent on the film orientation.The piezoresponse of the BNT thin films was represented exhibiting a strong orientation dependence that(110)>(001)>(111).This is contributed by the various domain switching contribution related to the crystal symmetry and polarization distribution in the three oriented thin films.

Synthesis and Piezoelectric Properties of Lead-free (Bi_(0.5)Na_ (0.5))_ 1-x(Ba_aSr_b)_xTiO_3 Ceramics

A new group of lead-free piezoelectric ceramics,（Bi0.5 Na0.5）1-x（BaaSrb）xTiO3（abbreviated as BNBST[100x-100a/100b],0〈x〈1,a＋b=1）,was synthesized.The ceramics were prepared by conventional ceramic sintering technique,and the ceramics with density of 95% of the theoretical one can be sintered without the atmosphere control during the sintering process.The results of the X-ray diffraction（XRD） data show that the ceramics possess a single perovskite phase.The measurements of dielectric and piezoelectric properties reveal that the ceramics provide relatively high piezoelectric charge constant d33 and high planar electromechanical coupling factor kp.For the BNBST6-95/5 ceramics,d33 is equal to 170pC/N,and kp is equal to 32.0%.The fabrication technique for these ceramics is conventional and stable.

Structure and Electric Properties of (1-x)(Bi_(1/2)Na_(1/2)) TiO_3-xBaTiO_3 Systems

The structural, dielectric and piezoelectric properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 ceramics were investigated for the compositional range, x=0.02, 0.04, 0.06, 0.08, 0.10. The samples were synthesized by a conventional solid-state reaction technique. All compositions show a single perovskite structure, and X-ray powder diffraction patterns can be indexed using a rhombohedral structure. Lattice constants and lattice distortion increase while the amount of BaTiO3 increases. The X-ray diffraction results show the morphotropic phase boundary （MPB） of （1-x）（Bi1/2Na12） TiO3-xBaTiO3 exists in near x=0.06-0.08. Temperature dependence of dielectric constant eT33/ε0 measurement reveals that all compositions experience one structural phase and two ferroelectric phases transition below 400℃： rhombohedral （or rhombohedral plus tetragonal） ferroelectric phase ←→ tetragonal antiferroelectric phase ←→ tetragonal paraelectric phase. Relaxor behaviors exist in the course of ferroelectric to antiferroelectric phase transition. Dielectric and piezoelectric properties are enhanced in the MPB range for （ 1-x）（Bi1/2Na1/2）TiO3-xBaTiO3.

Investigation of Ceramic Based Composites by Using 2D Graphene Filler

The ceramic composites of sodium bismuth titanate with reduce graphene oxide NBT/rGO of different compositions were fabricated by solid state sintering method and characterized. In this work, the graphene oxide (GO) and reduce graphene oxide (rGO) was successfully synthesized by Hummer’s modified method which is confirmed by FTIR and XRD results. The reduce graphene oxide used as 2D filler in piezoelectric creamic material. The crystalline structure of NBT/rGO composite was confirmed by X-ray diffraction with rhombohedral symmetry. The dispersion of rGO in the ceramic can be detect by the optical microcopy images. The electrical conductivity of sodium bismuth titanate shows increase at higher values of frequency and conductivity nanocomposites of different wt% were start decreases up to certain value of frequency. The broadening of peaks in frequency explicit plots of electrical conductivity with the help of LCR Meter (Impedance Capacitance and Resistance). The crystalline size of reduced graphene oxide and NBT is calculated by Scherrer’s formula of XRD peaks.

In-situ growth of hybrid NaTi8O13/NaTiO2 nanoribbons on layered MXene Ti3C2 as a competitive anode for high-performance sodium-ion batteries

In the work,we successfully explore a two-step hydrothermal method for scalable synthesis of the hybrid sodium titanate(NaTi8O13/NaTiO2) nanoribbons well in-situ formed on the multi-layered MXene Ti3C2(designed as NTO/Ti3C2).Benefiting from the inherent structural and componential superiorities,the resulted NTO/Ti3C2 composite exhibits long-duration cycling stability and superior rate behaviors when evaluated as a hybrid anode for advanced SIBs,which delivers a reversible and stable capacity of^82 mAh/g even after 1900 cycles at 2000 mA/g for SIBs.

Thermal Annealing and Graphene Modification of Exfoliated Hydrogen Titanate Nanosheets for Enhanced Lithium-ion Intercalation Properties

Hydrogen titanate has been considered as a promising lithium intercalation material due to its unique layered structure. In the present work, we fabricate 2D graphene/hydrogen titanate hybrid nanosheets for application as anode materials in lithium-ion batteries. H2Ti307 nanosheets are synthesized by exfoliation of a layered precursor via interacting bulky tetrabutylammonium （TBA＋） cations, followed by ion exchange with Na＋ ions and washing with water. The as-prepared hydrogen titanate nanosheets are well-dispersed exhibiting ultra-thin thickness with a lateral size up to a few micrometers. The sample is then annealed at 450, 650 Rnd 850 ℃, to optimize its Li＋-intercalation property. Heating at 450 ℃ leads to well-crystallized hydrogen titanate with a trace amount of TiO2. Heating at 650 and 850 ℃ results in mixed sodium titanates, since some sodium ions in the interlayer structure cannot be washed away and become chemically bonded to [TiO6] octahedra at high temperatures. Electrochemical properties of all the four samples are then evaluated by charged/discharged for 100 electrochemical cycles at 0.01-2.5 V vs. Li＋/Li at a specific current of 170 mA g-1. The unannealed hydrogen titanate delivers the highest initial discharge capacity of 130.5 mA h g-l, higher than 124.6 mA h g-1 from hydrogen titanate annealed at 450 ℃, as well as 101.3 and 63.8 mA h g-1 from hydrogen titanate annealed at 650 and 850℃, respectively, due to the high surface area from well-dispersed unannealed nanosheets. However, after 100 electrochemical cycles, well-crystallized hydrogen titanate annealed at 450 ℃ retain the highest charge capacity of 115.2 mA h g-1, corresponding to a capacity retention of 92.5%, while unannealed hydrogen titanate exhibits a final capacity of 72.1 mA h g-1 and a capacity retention of only 55.2%. To further improve energy density of lithium-ion battery, graphene/hydrogen titanate hybrid nanosheets are fabricated by adding graphene nanosheets into hydrogen titanates. The initial charge capacities of unannealed and annealed hydrogen titanate at 450 ℃ are significantly increased to 170.7 and 233.9 mA h g-1 , respectively. A charge capacity of 101.0 mA h g-1 is retained for unannealed hydrogen titanate with graphene-modification after 100 electrochemical cycles since well-dispersed hydrogen titanate nanosheets can be mixed with 2D graphene more uniformly and thus facilitates diffusion of Li＋ ions and retard aggregation of active materials.

Phase evolution in(1x)(Na_(0.5)Bi_(0.5))TiO_(3)-xSrTiO_(3) solid solutions:A study focusing on dielectric and ferroelectric characteristics

In the present work,the nature of phase evolution of(1x)(Na_(0.5)Bi_(0.5))TiO_(3)-xSrTiO_(3)(NBT-xST)solid solutions with x of 0e0.6 is revealed by characterizing the dielectric and ferroelectric properties.Two unique dielectric anomalies associated with high-temperature nanoregions(PNRs)in the ergodic relaxor(ER)state and low-temperature PNRs in the nonergodic relaxor(NR)state are identified.Characteristic temperatures,including TB,TRT*,Tm,Td and TT*,are determined in fresh and poled states on the basis of the characteristics of the evolution of these two dielectric anomalies.The whole evolution of the transition from the NR state to the ER state is reflected by the temperature-dependent polarization versus electric field(P-E)hysteresis loops,i.e.,from the square loops,via the double-like loops,to the slim loops.The characteristic temperatures,including TP-N,TN-R and TR-dis,are determined by the characteristics of the evolution of P-E loops.Accordingly,a phase diagram of NBT-xST was constructed according to these characteristic temperatures.Most importantly,the relationship between polarization responses and heterogeneous polar phase coexistence has been established and a schematic diagram is given.This work will help to understand the phase evolution and its impact on the macroscopic properties of NBT and the associated NBT-based solid solutions.

A REVIEW ON LEAD-FREE PIEZOELECTRIC CERAMICS STUDIES IN CHINA

There are a large number of research publications on the hot topic of environmental friendly leadfree piezoelectric materials worldwide in the last decade.The number of researchers and institutions involved from China is much larger than other countries or regions.The publications by Chinese researchers cover a broad spectrum on the preparations,structures,properties and applications of lead-free piezoelectric ceramics.This has motivated us to come out with a review on recent advances in development of lead-free piezoelectric ceramics in China.The emphases are especially on the preparation and electric properties of barium titanate-based materials,bismuth sodium titanate and related materials,alkaline niobate and related materials,bismuth layerstructured materials,as well as texture engineering of ceramics and some of their single crystals.Hopefully,this could give further impetus to the researchers to continue their e®orts in this promising area and also draw the attentions from legislature,research o±ce,industrial and publics.

Progress and perspective of high strain NBT-based lead-free piezoceramics and multilayer actuators

In this review,the evolution of high strain Na_(0.5)Bi_(0.5)TiO_(3)-based lead-free piezoceramics and their multilayer actuators has been explored.First,in terms of Na_(0.5)Bi_(0.5)TiO_(3)-based ceramic materials,the origin of high strain,the typical chemical modification methods of obtaining large strain and extrinsic factors affecting the large strain are discussed.Then it briefly summarizes the problems existing in Na_(0.5)Bi_(0.5)TiO_(3)-based ceramics for multilayer actuator applications.Strategies to optimize strain performance by means of microstructure control and phase structure design are also discussed.Thereafter,in terms of multilayer actuator,we describe its characteristics,applications and preparation process systematically,as well as the recent development of Na_(0.5)Bi_(0.5)TiO_(3)-based multilayer actuator.At last,perspectives on directions of following work and promising fields for the applications of the materials and their devices are presented.

Cubic multi-ions-doped Na_(2)TiO_(3) nanorod-like coatings:Structure-stable,highly efficient platform for ions-exchanged release to immunomodulatory promotion on vascularized bone apposition

The dissolution-derived release of bioactive ions from ceramic coatings on metallic implants,despite improving osseointegration,renders a concern on the interfacial breakdown of the metal/coating/bone system during longterm service.Consequently,persistent efforts to seek alternative strategies instead of dissolution-derived activation are pressingly carrying out.Inspired by bone mineral containing ions as Ca2+,Mg2+,Sr2+and Zn2+,here we hydrothermally grew the quadruple ions co-doped Na2TiO3 nanorod-like coatings.The co-doped ions partially substitute Na+in Na2TiO3,and can be efficiently released from cubic lattice via exchange with Na+in fluid rather than dissolution,endowing the coatings superior long-term stability of structure and bond strength.Regulated by the coatings-conditioned extracellular ions,TLR4-NFκB signalling is enhanced to act primarily in macrophages(MΦs)at 6 h while CaSR-PI3K-Akt1 signalling is potentiated to act predominately since 24 h,triggering MΦs in a M1 response early and then in a M2 response to sequentially secrete diverse cytokines.Acting on endothelial and mesenchymal stem cells with the released ions and cytokines,the immunomodulatory coatings greatly promote Type-H(CD31hiEmcnhi)angiogenesis and osteogenesis in vitro and in vivo,providing new insights into orchestrating insoluble ceramics-coated implants for early vascularized osseointegration in combination with long-term fixation to bone.

Dielectric behaviors and relaxor characteristics in Bi_(0.5)Na_(0.5)TiO_(3)-BaTiO_(3) ceramics

Microstructure and dielectric behaviors of heating/cooling and bias-field were investigated in lead-free ceramics(1-x)Bi_(0.5)Na_(0.5)TiO_(3)-xBaTiO_(3)(BNT-xBT,x=0,0.02,0.04,0.06,0.08 and 0.10).The relaxor characters and the Vogel–Fulcher law of frequency-dependent dielectric properties were analyzed.Three dielectric anomalies with pronounced frequency dispersion at Td,a maximum dielectric with variable frequency-dispersion at Tm and a third Maxwell–Wagner-type relaxation over a wide temperature range in high-temperature region were observed.The significant dielectric thermal hysteresis,low barrier energy,high freezing temperature in heating process and the maximum dielectric tunability appeared in x=0.4 ceramic.

ENHANCED PIEZOELECTRIC PROPERTIES IN(Bi_(0.5)K_(0.5))TiO_(3)-(Bi_(0.5)Na_(0.5))TiO_(3)FERROELECTRIC SINGLE CRYSTALS

Single crystals of x(Bi,K)TiO_(3)-(1-x)(Bi,Na)TiO_(3)(0.11≤x≤0.47) were grown by a flux method and their polarization and piezoelectric properties were investigated along h100i cubic at 25℃.Rietveld analysis of powder X-ray diffraction data provides a tentative phase diagram in this system.rhombohedral R3c for x≤0.22,pseudocubic for 0.22<x<0.3 and tetragonal P4mm for 0.3≤x.Piezoelectric strain properties show that the crystals(x=0.38)exhibited an extremely large piezoelectric strain constant of 637 pm/V.

Structure and Piezoelectric Properties of Lead-Free Na_(0.5)Bi_(0.5)TiO_3 Nanofibers Synthesized by Electrospinning

Lead-free Na0.5Bi0.5TiO 3（NBT） nanofibers with the perovskite structure were prepared by the electrospinning method.The nanofibers were about 200-300 nm in diameter and up to several hundred microns in length.The crystal structures and morphologies of the nanofibers were characterized by X-ray diffraction（XRD）,Raman spectroscopy,scanning electron microscopy（SEM）,and transmission electron microscopy（TEM）.The effective piezoelectric property of individual NBT nanofiber was examined by piezoresponse force microscopy（PFM）.The NBT nanofibers crystallized in pure perovskite phase after annealing above 700℃in air and comprised a great number of fine particles with size of 60-80 nm.In addition,the electromechanical energy conversion models for NBT nanofibers were built and demonstrated high voltage output as high as several millivolts.Such a result qualifies NBT nanofibers as a promising candidate for leadfree electromechanical conversion devices.

Effect of rare earth on physical properties of Na_(0.5)Bi_(0.5)TiO_(3)system:A density functional theory investigation

Na_(0.5)(Bi_(3/4)RE_(1/4))_(0.5)TiO_(3)(RENBT,RE=Nd,Gd,Dy,and Ho)compounds were investigated in the framework of first-principles calculations using the full potential linearized augmented plane wave(FP-LAPW)method based on the spin-polarized density functional theory implemented in the WIEN2k code.Combined charge density distribution and Ti K-edge X-ray absorption spectra reveal that the RENBT compositions with high polarization values are accompanied by a higher TiO_(6)distortion,DyNBT,and NdNBT compounds.The effect of the rare-earth elements on the polarization is confirmed experimentally with the collection of the hysteresis loops.The investigation of the electronic properties of the compounds highlights the emergence of a magnetization owing to the 4f orbital effect of the rare-earth elements.Besides,the investigation of the chemical ordering shows a short-range chemical ordering for the pure composition and an increased A-site disorder for dysprosium doped NBT system.The increased disorder may speak for increased relaxor properties in the RE doped compositions.

NaNbO_(3) modulated phase transition behavior and antiferroelectric stability evolution in 0.88(Bi_(0.5)Na_(0.5))TiO_(3)-0.12BaTiO_(3) lead-free ceramics

Giant strains in(Bi_(0.5)Na_(0.5))TiO_(3) based ceramics are usually attributed to electric field induced nonpolar to polar phase transition.Whether it is an ergodic relaxor R3c/P4mm ferroelectric(FE)to long-range ordered FE phase transformation or a reversible P4bm antiferroelectric(AFE)to FE phase transition is still unclear.Herein,lead-free(0.88-x)(Bi_(0.5)Na_(0.5))TiO_(3)-0.12BaTiO_(3-x)NaNbO_(3) ceramics exhibit a compositionmodulated FE tetragonal P4mm to relaxor AFE tetragonal P4bm phase transition,in which double hysteresis loop,sprout-shaped S-E curves,near-zero quasi-static d33 together with a large volume change suggest the AFE characteristics of P4bm phase.An interesting finding is that the reversibility of fieldinduced AFE P4bm phase to FE P4mm phase transition strongly depends on the NN content,from being completely irreversible at x=0.01e0.02,to partially reversible at x=0.03e0.05,and finally to completely reversible at x=0.06e0.08.It is indicated that the variation of reversibility should be attributed to the change of relative free energy caused by decreasing the FE to AFE phase transition temperature with increasing the NN content.

Structural and Dielectric Properties of ZnO Added (Na_(1/2)Bi_(1/2))TiO_3 Ceramics

Structural and dielectric properties of polycrystalline samples of lead-free （l-x）（Nal/2Bil/2）TiO3-xZnO, prepared using a high-temperature solid-state reaction method, were investigated in the composition range of 0≤x≤0.10. Rietveld analyses of X-ray diffraction data indicated the formation of a single-phase hexagonal structure with R3c symmetry. Williamson-Hall approach was applied to estimate the apparent particle size and lattice strain of the compounds. Temperature dependence of dielectric constant showed that the addition of ZnO to （Na1/2Bi1/2）TiO3 shifted the phase transition temperature towards higher side, a property favourable for practical applications of these ceramics. Further, temperature dependent permittivity data provided low temperature coefficient of capacitance （TCC〈8%） up to 100℃. Furthermore, a decrease in the value of dielectric loss with an increase in ZnO content was observed.