•A unique hydrothermal process, high temperature mixing method under hydrothermal condition (HTMM), was developed.•The grain size of BST and NaNbO3 crystals were decreased by HTMM.•Assembled porous structures were constructed by HTMM.•Formation mechanism was elucidated from the viewpoint of nucleation and grain growth.Crystal size and microstructure are of great importance in determining the physical and chemical properties of functional materials, and refine powders, especially their assembled porous structures have potential application in ceramic fabrication, absorption, catalysts and drug delivery, due to their characters of high activity and large specific surface area. Herein, high temperature mixing method under hydrothermal condition (HTMM) was adapted to synthesize barium strontium titanate [(Ba, Sr)TiO3, BST] powders with various Ba/Sr ratios (x = 0.5, 1.0, 3.0 and 4.0). In comparison with conventional hydrothermal synthesis (CHS), the effects of HTMM on grain refinement and porous structure formation were exclusively investigated. XRD and SEM results indicated that, in the given condition, BST powders prepared by HTMM were much smaller than that by CHS, especially at a lower Ba/Sr ratio. Additionally, assembled porous architectures were constructed by HTMM. It's believed that the high temperature mixing process and continuous rotation contributed to the grain refinement and assembled porous structure, respectively. The assumption was further confirmed through the synthesis of sodium niobate (NaNbO3) powders by HTMM. It's demonstrated that HTMM is advantageous in preparation of refine powders and porous assembled architectures.

Nanomaterials, especially graphene-like 2D ultrathin ones that possess a wealth of unprecedented functionalities, can increase the discharge capacity of Li-ion batteries (LIBs), but they still suffer from poor cycling and rate performances due to their serious self-aggregation and pulverization. Constructing micro/nano-structures is a quite promising method to address the above issues. However, it remains a huge challenge to build 3D hierarchical porous micro/nano-structures self-assembled from ultrathin nanostructured building blocks, which has prompted extensively great interest. Herein, we report a facile “hydrolysis–controllable crystallization” strategy to controllably synthesize different dimensional (i.e. 1D, 2D, and 3D) VO2 (B) nanostructures by a simple one-step high-temperature mixing method under hydrothermal conditions. In particular, unique 3D micro/nano-structured hierarchical porous sponge-like micro-bundles (SLMBs) self-assembled from 2D crumpled ultrathin VO2 (B)@C nanosheets with a thickness of only ∼3.1 nm (denoted as VO2 (B)@C-SLMBs) are synthesized. This is the first report on the synthesis of 2D ultrathin VO2 (B) nanomaterials. Importantly, the intrinsic VO2 (B) crystallization behavior and controllable synthesis mechanism of VO2 (B) micro/nano-structures are revealed for the first time by the density functional theory calculation. The as-synthesized VO2 (B)@C-SLMBs possess distinct structural advantages, i.e., large surface area, abundant meso/micropores, robust structure and conductive carbon frameworks, which make them exhibit excellent electrochemical performance in terms of long life, high rate, and large capacity as cathode materials of LIBs. The discharge capacity was 206 mA h g−1 after 160 cycles at 100 mA g−1, corresponding to 105% of the initial capacity. Even at a large current density of 1000 mA g−1, they still exhibit a high retention of 104% after long period of 1000 cycles. These results indicate that the as-synthesized VO2 (B)@C-SLMBs have a great potential for long-life and high-rate cathode materials of next-generation LIBs.

Nanomaterials, especially graphene-like 2D ultrathin ones that possess a wealth of unprecedented functionalities, can increase the discharge capacity of Li-ion batteries (LIBs), but they still suffer from poor cycling and rate performances due to their serious self-aggregation and pulverization. Constructing micro/nano-structures is a quite promising method to address the above issues. However, it remains a huge challenge to build 3D hierarchical porous micro/nano-structures self-assembled from ultrathin nanostructured building blocks, which has prompted extensively great interest. Herein, we report a facile “hydrolysis–controllable crystallization” strategy to controllably synthesize different dimensional (i.e. 1D, 2D, and 3D) VO2 (B) nanostructures by a simple one-step high-temperature mixing method under hydrothermal conditions. In particular, unique 3D micro/nano-structured hierarchical porous sponge-like micro-bundles (SLMBs) self-assembled from 2D crumpled ultrathin VO2 (B)@C nanosheets with a thickness of only ∼3.1 nm (denoted as VO2 (B)@C-SLMBs) are synthesized. This is the first report on the synthesis of 2D ultrathin VO2 (B) nanomaterials. Importantly, the intrinsic VO2 (B) crystallization behavior and controllable synthesis mechanism of VO2 (B) micro/nano-structures are revealed for the first time by the density functional theory calculation. The as-synthesized VO2 (B)@C-SLMBs possess distinct structural advantages, i.e., large surface area, abundant meso/micropores, robust structure and conductive carbon frameworks, which make them exhibit excellent electrochemical performance in terms of long life, high rate, and large capacity as cathode materials of LIBs. The discharge capacity was 206 mA h g−1 after 160 cycles at 100 mA g−1, corresponding to 105% of the initial capacity. Even at a large current density of 1000 mA g−1, they still exhibit a high retention of 104% after long period of 1000 cycles. These results indicate that the as-synthesized VO2 (B)@C-SLMBs have a great potential for long-life and high-rate cathode materials of next-generation LIBs.

Fabrication of free -standing binary transition metal oxides, especially NiCo2O4, has attracted significant research interests since these metal oxides are promising candidates for free-standing anodes of lithium-ion batteries (LIBs). However, there remain some problems, especially low loading, for the existing NiCo2O4 anodes. To address the abovementioned issue, it will be a quite feasible solution to combine the advantages of both hierarchical micro/nano-structures and free-standing electrodes to fabricate a free-standing hierarchical micro/nano-structural NiCo2O4 electrode. Herein, we proposed an effective method to controllably synthesize hierarchical bilayered hybrid nanostructural arrays of NiCo2O4(HNAs) micro-urchins and nanowires, denoted as NiCo2O4 HNAs/NF, based on Ni foam (NF) with a high loading via a simple surfactant-assisted hydrothermal and subsequent annealing treatment. In this synthesis, NF was applied as a Ni source for NiCo2O4 without the addition of other Ni-containing reagents, and the pH value played an important role in the synthesis of NiCo2O4 HNAs/NF. Furthermore, the reasonable reaction mechanism of NiCo2O4 HNAs/NF has been discussed in detail and proposed. The as-synthesized NiCo2O4 HNAs/NF possess unique structural advantages such as a large surface area, hierarchical porous structures, and robust connection of NFs and NiCo2O4 active materials. Thus, these unique NiCo2O4 HNAs/NF display excellent electrochemical performance such as a large reversible capacity of 1094 mA h g−1 at a current density of 500 mA g−1 and a good rate capability of 875 mA h g−1 at a large 1000 mA g−1. Especially, a high loading (7 mg cm−2) of NiCo2O4 HNAs/NF, which is much higher than those of other NiCo2O4 electrodes, is beneficial towards the achievement of lightweight and miniaturized LIBs.

With the wearable electronics progressing rapidly, the demand for flexible, long-life and low-cost electrodes of Li-ion batteries (LIBs) becomes more and more urgent. Due to the abundant resources and low cost, silica (SiO2), especially the amorphous one, has attracted a lot of interests on the application of anode materials for LIBs. However, SiO2 still suffer from the poor cycling performance mainly caused by the huge volume change during cycling like other alloy-type materials. Furthermore, it remains a challenge to fabricate the SiO2–based flexible electrode. Herein, we propose a facile in situ strategy to fabricate the electrospun robust free-standing SiO2/carbon nanofibers (denoted as in-SCNFs) film constructed by N-doped carbon nanofibers encapsulating uniformly amorphous SiO2 nanoparticles. The in situ synthesized finer SiO2 nanoparticles in the in-SCNFs are uniformly encapsulated in flexible carbon nanofibers, which can effectively buffer the volume change. Furthermore, the robust in-SCNFs film possesses the excellent mechanical flexibility and strength. So, when served as the free-standing anode of LIBs, the in-SCNFs film exhibits superior cycling performance. A discharge specific capacity of 405 mAh/g can be delivered even after a long-term 1000 cycles at a large current density of 500 mA/g, and the retention is up to 115%. It is an exciting finding that the in-SCNFs film is also a long-life anode of Na-ion batteries (NIBs). The 99% of initial capacity can be kept after 250 cycles at 500 mA/g. To our best knowledge, this is the first report on the application of SiO2/C composite for NIBs. These results suggest that the as-fabricated in-SCNFs film can become one promising free-standing long-life anode for LIBs and NIBs.

•AgBr nanoparticles interspersed MoO3 nanobelts photocatalyst was synthesized by an oriented diffusing and charge induced deposition method.•Ultra-short photocatalytic time (5 min) and Ultra-high degradation efficiency (95%).•Noticeable photocurrent response was detected under visible light irridiation, and O2− was confirmed to be a dominant reactive specie by experiments.•Dye-sensitized-assisted electron transfer process was proposed.•Redox ability of electrons was enhanced by photon-generated carriers recombination on the ohmic contact interface.Inspired by the natural photosynthesis in green plants, artificial heterogeneous Z-scheme photocatalytic systems are widely used to settle environmental concerns and energy crises, and their excellent characteristics come from long-term stability, wide absorption range, high charge-separation efficiency, and strong redox ability. However, the contribution of the surface-adsorbed dyes antenna molecule is seldom considered in the process of Z-scheme photocatalysis. In this study, we construct AgBr quantum dots decorated MoO3 nanobelts as a novel Z-scheme photocatalyst by an oriented diffusing and charge induced deposition. For the first time, we find the synergistic effect caused by the suitable energy band match among RhB dyes, AgBr nanoparticles, and MoO3 nanobelts, leading to the ultrafast dye-sensitized-assisted electron transfer process. This is responsible for excellent photocatalytic activities of the achieved AgBr/MoO3 monolithic catalyst for degrading RhB under visible light irradiation. Simultaneously, changing of the band gaps and detailed mechanism for high efficiency degradation is analyzed and explored by theoretical calculations and designing further experiments. It is proposed that ultrafast degradation of the RhB on the AgBr/MoO3 nanocomposites is due to both the photocatalytic process and the dye sensitization; the superoxide radical O2−, which is produced by accumulated dye-sensitization-induced abundant electrons with powerful potential in the CB of AgBr accompanying by quick combination of electrons in the CB of MoO3 with photogenerated holes in the VB of AgBr, is a dominant reactive species for the degradation of RhB under visible light irradiation.Download high-res image (186KB)Download full-size image

High-quality lead-free piezoelectric xMn-doped (K0.48Na0.52)0.985Li0.015NbO3 films (KNLN; x = 0, 0.01, 0.02, 0.03) were successfully deposited onto Pt(111)/Ti/SiO2/Si(100) substrates by sol–gel method. Effects of Mn substitution on the microstructure, dielectric properties, ferroelectric properties, and leakage current of the KNLN films were investigated in detail. Mn-doping can significantly improve the ferroelectric properties and decrease the leakage current of KNLN films. Optimal dielectric properties were obtained in films doped with 2 mol% Mn, whose dielectric constant and dielectric loss at 1 kHz were 875 and 0.030, respectively. In addition, well-saturated ferroelectric P-E hysteresis loop with large remanent polarization (2Pr) and coercive field (Ec) of 22.5 μC/cm2 and 65 kV/cm were obtained in 2 mol% Mn-doped KNLN film at an applied electric field of 200 kV/cm.

In this study, ilmenite-type NaNbO3 microplates were prepared by a facile surfactant-free method, using NaAc and KOH as a sodium resource and as a mineralizer, respectively. The effects of each reactant were identified, and the formation process and crystallization pathway of ilmenite-type NaNbO3 microplates were explored based on the phase constitution, microstructure and chemical compositional analysis. The indispensable roles of K ions, which participated in the formation of layered KNN-hydrate intermediates, were revealed. Ilmenite-type NaNbO3 microplates were formed by the dissolution of these intermediates and subsequent recrystallization into K-containing NaNbO3, followed by the ion-exchange between K and Na ions. Meanwhile excess K ions would hinder the release of K ions associated with the dissolution of intermediates, thus preventing the formation of ilmenite-type NaNbO3. Moreover, the morphological evolution of ilmenite-type NaNbO3 microplates from platelets to octahedra was interpreted in terms of their intrinsic structure and KOH concentration.

Bundle-like α′-NaV2O5 mesocrystals were synthesized successfully by a two-step hydrothermal method. Observations using electron microscopy revealed that the obtained NaV2O5 mesocrystals were composed of nanobelts with the preferential growth direction of [010]. The precise crystal structure was further confirmed by Rietveld refinement and Raman spectroscopy. Based on analysis of crystal structure and microscopy, a reaction and growth mechanism, hydrolysis–condensation (oxolation and olation)-ion exchange-self-assembly, was proposed and described in detail. Furthermore, electrochemical measurements were used to analyze the Na-ions intercalation/deintercalation abilities in NaV2O5, and indicated that Na-ions were difficult to extract. Importantly, the DFT theoretical calculation results, which showed that the migration energy of Na-ions was so huge that migration of Na-ions was quite difficult, can explain and support well the results of the electrochemical measurements.

•Monocrystalline bundles and polycrystalline nanowires are synthesized via an in-situ reaction.•The polycrystalline nanowires are more activated.•The high capabilities of the polycrystalline nanowires are mainly attributed to rapid Li+ diffusion.In this article, monocrystalline bundles and polycrystalline nanowires were synthesized using α-MnO2 and MnOOH as precursors via an in-situ reaction. The electrochemical properties of the resulting nanocrystals were investigated. Results reveal that the polycrystalline nanowires are more activated than the monocrystalline nanowires. The polycrystalline nanowires also deliver a maximum discharge capacity of 226 mA h/g at 10 mA/g. Compared with the linear charging plateau at >4.3 V in the monocrystalline bundles, the charging platues of (100) and (001) domains in the polycrystalline nanowires are 4.3–4.55 and 4.55–4.6 V, respectively. The high capacity and rate performance of the polycrystalline nanowires are attributed to their good electroconductivity and rapid Li+ diffusion, which originate from defects and small domains.

Monodisperse Dy-doped BaTiO3 nanopowders (xDBT) with x=0, 1, 2, 3, 4, 5 mol% has been synthesized via a modified sol-hydrothermal method. And the influence of Dy3+ on the crystal structure, micromorphology and dielectric properties of xDBT ceramics has been investigated. It’s found that Dy3+ slightly affects the shape of the xDBT nanopowders, whereas excess Dy3+ would cause the formation of the Dy(OH)3 impurity. In addition, the grain growth during a sintering process is suppressed with the Dy3+ incorporation. Further, the possible occupation of the Dy3+ has been extrapolated based on the variation of lattice volume and phase composition. A self-compensation mode involving the simultaneously occupation at Ba-site and Ti-site is observed in the samples with 4 mol% Dy. Importantly, stabilized temperature-dependent dielectric properties has been achieved at x=4 mol%, resulting from the diffuse phase transition behaviors (the calculated diffuse factor γ=1.952) induced by chemical inhomogeneity.

Molybdenum disulfide (MoS2) has emerged as a promising electrocatalyst for hydrogen evolution reaction (HER). However, the performance of the catalyst suffers from the scarce active sites and poor electrical conductivity. Here we grow vertical MoS2 films on Mo foils to achieve highly catalytic active sites and enhanced electrical conductivity for facilitating high efficient HER catalysis. The ultrathin nanofilm with a thickness of around 4 nm on molybdenum foils is grown by a two-step method: (1) the molybdenum oxide (MoO2) nanofilm is achieved by oxidizing the surface of the Mo foil under a low pressure condition and (2) a MoS2 nanofilm is obtained by sulfurizing the MoO2 nanofilm in sulfur vapor at 700 °C within 1 min. Furthermore, the vertically aligned MoS2 nanofilm on Mo foils exhibit excellent stability in acidic solution and the electrochemical measurements show an onset overpotential of as low as 18 mV and a small Tafel slope of 55 mV/dec. The excellent HER catalysis originates from the synergistic effect of the dense catalytic active sites at the vertical MoS2 surface and superior electron transport along the Mo foil. This study opens a novel avenue for the development of earth-abundant, low-cost electrocatalysts with high HER activities.

A remarkably simple and effective high-temperature mixing method under hydrothermal conditions was applied to synthesize well-crystallized V3O7·H2O nanobelts, VO2 (B) nanosheets and VO2 (A) nanorods with good performances for Li-ion batteries. In particular, V3O7·H2O exhibited an excellent electrochemical performance. The outstanding electrochemical properties were explained through analysis of the crystal structures.

•Using a low-temperature solid-state method, ZnO/CdS nanocomposites were obtained•Grain growth kinetics of cubic CdS and hexagonal ZnO phase was described.•Sufficient grinding and heating treatment was a key for formation of composites.•Optical properties could be easily manipulated by reaction temperature and time.A simple low-temperature solid-state reaction in the presence of the surfactant PEG400 was developed to obtain ZnO/CdS nanocomposites. The effects of synthesis temperature and reaction time on crystal structure and optical properties of the nanocomposites were investigated by several technologies. X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) characterizations showed that the products consisted of the nanoparticles, and the grain growth kinetics of the cubic CdS and the hexagonal ZnO phase in the nanocomposites was described. The mechanism analysis suggested that sufficient grinding and heating treatment was a key to form the ZnO/CdS nanocomposites, and the surfactant PEG400 was proved not to involve the reaction and prevent the nanoparticles from aggregating to larger in whole grinding and heat-treatment process. Ultraviolet–visible (UV–vis) spectra revealed that the band gaps of the nanocomposites could be tuned by the reaction temperature and reaction time. Photoluminescence (PL) spectra showed that the changing position and the intensity of the emission peaks resulted from the rate of electron transfer and recombination probability under the different conditions.

In this article, we report the synthesis of Li2MnO3 nanocrystals using a hydrothermal process. XRD, SEM, and TEM analyses are performed, and the electrochemical properties of the resultant nanocrystals are investigated. Adding the oxidant KMnO4 influences the phase purity, size, and shape of the Li2MnO3 nanocrystals. An amount of KMnO4 that exceeds 6% of the total Mn source enhances the formation of the pure monoclinic Li2MnO3 phase. The effect of the amount of KMnO4 on Li2MnO3 grain size can be divided into three ranges. Li2MnO3 crystals with a size around 28.7 nm and plate morphology are obtained at less than 6% of KMnO4 content; those with a size of 28.7 nm to 9.8 nm and mixed morphology of plates and rods are obtained at 6% to 11% KMnO4 content, and those with a size around 9.8 nm and rod morphology are mainly obtained at KMnO4 content exceeding 11%. Discharge capacities increase with decreasing size of Li2MnO3 nanocrystals in a linear relationship. The voltage of the first charge shows a 4.55 V plateau for Li2MnO3 nanocrystals with 28.7 nm size, becoming 4.4 V with a decrease in size to 12.2 nm, and splitting into two plateaus at around 3.8 and 4.4 V with a further decrease in size to 9.8 nm. The XRD and XANES results of the Li2MnO3 electrodes obtained after charge/discharge experiments show that smaller sizes are more beneficial in maintaining a layered structure than larger nanocrystals.

To further improve the photocatalytic H2 evolution activity, NaNbO3 photocatalyts simultaneously possessing cubic crystal structure and 1D morphology have been successfully synthesized via a modified solvothermal strategy. During the process of synthesis employing ethylene glycol as solvent, a temperature fluctuation during the autoclaving period is proposed to regulate the grain growth without any other additives or calcinations. It is demonstrated that the structure-directing effect of the solvent is enhanced in the condition of the temperature fluctuation, contributing to the formation of 1D nanostructure. Otherwise, the irregular NaNbO3 nanoparticles with severe aggregation resulted. Photocatalytic H2 evolution activities of samples under ultraviolet light irradiation with 0.5 wt % of Pt cocatalyst indicate that NaNbO3 nanowires expectedly exhibit an enhanced activity of 699 μmol h–1 g–1, approaching twice that of NaNbO3 nanoparticles. The higher photocatalytic activity of NaNbO3 nanowires is attributed to their large specific surface area, high chemical purity, and powerful reduction ability, which have been confirmed by the further characterizations and analysis based on crystal structure, valence state, elemental composition, and energy band structure. The modified solvothermal strategy provides an alternative pathway to regulate the crystal growth, which can effectively integrate the unique morphology with desired crystalline structure toward increasing photocatalytic activity.

One dimensional (1D) NaNbO3 powders have attracted increasing attention for their excellent photo-catalytic and piezoelectric properties, and the stable, moderate and low-energy synthesis of the targets is highly desirable. Herein, a facial solvothermal strategy is adapted to synthesize the one-dimensional (1D) rod-like precursors Na7(H3O)Nb6O19·14H2O by using isopropanol as the reaction medium. When the precursor is subjected to post-heating treatments, rod-like orthorhombic as well as approximate ellipsoid-like monoclinic NaNbO3 powders are obtained. Corresponding mechanisms for the stable solvothermal synthesis, morphological evolution and phase transition are further proposed and discussed.

Well-crystallized, ultra-long VO2 (A) nanorods were synthesized using a facile high-temperature mixing method (HTMM) under hydrothermal conditions. The as-obtained products were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis-NIR, differential scanning calorimetry and Fourier transform infrared spectroscopy. The effect of W doping on the phase-transition properties of VO2 (A) was also studied. The results indicate that the optimal synthesis condition of VO2 (A) using the HTMM is hydrothermal treatment at 240 °C for 48 h with a 3:1 molar ratio of the reducing agent to the vanadium source. The reason why the polymorphic forms of VO2 show different colors is that the light in the visible region reflected by the samples is different. The phase-transition temperature of the pure VO2 (A) is 154.75 °C, which is significantly lower than the 162 °C reported previously. When a small amount of W is doped, VO2 (A) will be transformed into other polymorphic forms, which indicates that the crystal structure of VO2 (A) is highly sensitive to limited doping. Importantly, the as-obtained pure VO2 (A) shows good thermochromic properties and optical-switching characters. A crystal growth mechanism for VO2 (A), oriented-attachment–exfoliation–recrystallization–oriented-attachment, is proposed and described in detail.

We present a novel low-temperature sol-solvothermal method to synthesize fine lead zirconate titanate (PZT) particles. This sol-solvothermal method combines the advantages of conventional sol–gel process and the solvothermal method, and isopropyl alcohol (IPA) was used as the solvent. The effects of different parameters including KOH concentration, IPA/(IPA + water) ratio and reaction temperature, on the microstructures of the PZT powder were studied. With increasing KOH concentration and reaction temperature, the crystalline structure of as-synthesized PZT transformed from tetragonal to rhombohedral phase. More IPA added in the solvent can effectively reduce agglomeration of the PZT powder and decrease the crystallization temperature, but impurity phase was also detected at high IPA/(IPA + water) ratio. As a result, the synthesis parameters are optimized, and well-crystallized 700 nm PZT particles were successfully synthesized in 2.0 M KOH and 50 % IPA/(IPA + water) ratio at temperatures as low as 120 °C.

We describe the synthesis of hexagonal NaNbO3 by mixing reactants at high temperature under hydrothermal conditions. The morphological and structural evolution of crystalline NaNbO3 was studied in detail using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, and Raman techniques. A variety of products in the form of irregular Na8Nb6O19·nH2O bars, microporous monoclinic Na2Nb2O6·nH2O fibers, self-assembled dandelion-like Na2Nb2O6·nH2O structures, and octahedral-shaped hexagonal NaNbO3 have been prepared. The present synthetic strategy enables us to tune the morphologies and structures of the niobate products by controlling the reaction kinetics.

The present research describes a modified sol-gel technique used to obtain nano-crystalline potassium niobate (KNbO3) powders by using ethylene diamine tetraacetic acid (EDTA)/citrate as a complexing agent. The metal ions chemically interact with EDTA in the precursor sol. The aging treatments lead to the formation of a precursor-polymeric gel network. The effects of the amounts of citric acid and EDTA on the stability of the precursor sol are investigated. The influence of excess K on the formation of pure-phase KNbO3 powders is also studied. The obtained gels and powders are characterized by thermogravimetric-differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that a stable precursor sol is formed when n(CA):n(Mn+) = 3:1 and n(EDTA) :n(NH4OH) = 1:3.5. The xerogel is calcined at 700–850 °C to prepare the KNbO3 nano-powder. The smallest grain size of the sample obtained at 850 °C is about 60 nm when the K/Nb molar ratio equals 1.2.

A 0.655Pb(Mg1/3Nb2/3)O3-0.345PbTiO3 (PMN-0.345PT) functionally graded (FG) piezoelectric actuator was fabricated by tape-casting. The effects of sintering temperature on the physical and electrical properties of the PMN-PT ceramics were initially investigated. High dielectric and piezoelectric properties of d33 = 700pC/N, kp = 0.61, εr = 4.77 × 103, tanδ = 0.014, Pr = 30.68 μC/cm2 were obtained for the specimens sintered at 1200°C. Compared with the traditional solid-state reaction, the properties of the ceramics were significantly enhanced by tape-casting. The new FG piezoelectric actuator consisted of four layers, and the variation of changes in their d33 and εr were graded opposite the thickness direction. The relationship between displacement and voltage for the actuator was also determined, with the results showing that it was linear. The driving displacement of the free end of the actuator reached 430.668 μm.

Pure (K,Na)NbO3 (KNN) powders have been successfully prepared by using traditional hydrothermal method and high-temperature mixing method (HTMM) under solvothermal and hydrothermal conditions. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to show the change of phase, morphology, and size of the as-prepared particles with the alkalinity of the starting solution. Compared with the traditional hydrothermal method, smaller particles with higher phase purity are prepared using HTMM under hydrothermal conditions. It is found that the alkalinity has significant effects on the crystal size. The KNN grain size first increases and then decreases with increasing alkalinity. Typical samples solvothermally synthesized in a mixed solvent with isopropanol/deionized water ratio of 50/50 by volume were made of well-crystallized single-crystalline nanoparticles with size of about 500 nm.

(K, Na)(Nb, Sb)O3 (KNNS) lead-free peizoceramic powders were successfully synthesized by hydrothermal treatment at 240 °C for 8 h using the KOH, NaOH, Nb2O5 and Sb2O3 as raw materials. Effects of Sb-doping on the crystal structure and morphology of the as-prepared powders were investigated by powder X-ray diffraction (XRD), Raman spectra (Raman), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The Sb element was successfully doped into the alkaline niobate perovskite structure to form crystalline (K0.7Na0.3)(Nb0.95Sb0.05)O3 lead-free piezoelectric ceramic powder, which has a hexagonal morphology due to the aggregation growth of small grains. Phase and morphology evolutions with the reaction time were also studied, and a possible formation mechanism was proposed.

In order to prepare the pure (K, Na)NbO3(KNN) particles with higher crystallinity, the high temperature mixing method (HTMM) under hydrothermal conditions was carried out in this work. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM). The results indicate that the KNN particles size decrease gradually with the increase of mineralization concentration in the starting solution. The ratio of K+/(K+ + Na+) in the starting solution has a great effect on the phase of the products, and several phases coexist in the product when the ratio of K+/(K+ + Na+) in the starting solution is 0.7.

The solid solutions in the system of Ca and Pb hydroxyapatite, Ca10−χPbχHA (χ = 0–10), were successfully synthesized by high-temperature mixing method (HTMM) at 200 °C for 12 h under hydrothermal conditions. The samples were characterized by X-ray diffraction, chemical analysis and electron microscopic observation, and the site of the metal ions in the solid solutions was analyzed with the Rietveld method. The lattice parameters of the solid solutions prepared by both of the methods didn’t vary linearly with Pb contents, and they have two turning points of 0.4 and 0.6 of Pb content. It was found that Pb ions in the solid solutions preferentially occupied the M (2) site in the apatite structure. HTMM gives Ca–Pb HA solid solutions much better crystallization. However, due to the formation of intermediate compound of Pb3O2(OH)2 in the Pb(NO3)2·4H2O solution before mixing with (NH4)2HPO4 solution at 200 °C, HTMM causes the decrease of crystallization of the samples with high Pb content.The Ca–Pb HA solid solutions were prepared by High-temperature mixing method (HTMM) under hydrothermal conditions. Metal ion occupancy of Ca–Pb HA solid solutions was analyzed by Rietveld method. It is found that Pb ions in the solid solutions preferentially occupy M (2) site in the apatite structure.

Cadmium hydroxyapatite (Cd HAp) pure crystals were synthesized by high temperature mixing method under hydrothermal conditions using the solutions of Cd(NO3)2·4H2O and (NH4)2HPO4. The influences of pH values and reaction time on the structure and morphology of Cd HAp crystals were investigated. The results indicate that the pH value has a great influence on the morphology which varies from bulk-like to fiber with the increase of the pH value. The intermediate phase of Cd5H2(PO4)4·4H2O is formed in the weak alkali reaction medium of (NH4)2HPO4 at pH 9, and it take long time to be dissolved and changed into pure phase of bulk-like Cd HAp crystal. In the strong alkali reaction medium of (NH4)2HPO4 solution at pH 11, the intermediate phase of Cd2P2O7·5H2O is formed, and then dissolved, and rapidly changed to pure phase of Cd HAp fiber. Cd3(OH)5NO3 crystals are formed in the nitrate solution before mixing at 200 °C, its influences on crystallinity, morphology and size of Cd HAp crystals were also discussed.

•Tree-like Li2MnO3@CNT hierarchical architecture is synthesized via an in-situ hydrothermal reaction.•Li2MnO3@CNT hybrid exhibits superior reversible capacity, cycling stability and rate capability.•Li2MnO3@CNT hybrid delivers an increasing capacity upon cycling.•The conversion from LiOH to Li2O and LiH may contribute to surface-enhanced lithium storage for additional capacities.The increasing demand for high-energy-density portable electronics and electric vehicles is sparking an intensive research interest in lithium-ion batteries. Transition metal oxides/carbonaceous matrix hybrids have attracted tremendous attention to produce the next-generation lithium-ion batteries (LIBs). This paper initially reports that the tree-like Li2MnO3@carbon nanotube (CNT) hierarchical architecture can achieve the long-life lithium storage performance. Li2MnO3 nanoparticles of the hybrid with lattice Li+, as the anode material for LIBs, exhibits a reversible capacity of over 740 mAh/g at a current density of 0.5 A/g after 350 cycles, indicative of superior cyclic stability and excellent rate performance. XPS and XRD patterns reveal that LiOH in the anode material, which originates from the conversion reaction, is further discovered to be available and reversible for surface-enhanced lithium storage. Surface-enhanced lithium storage contributes to the over-compensation and increased capacity.

Nanomaterials, especially graphene-like 2D ultrathin ones that possess a wealth of unprecedented functionalities, can increase the discharge capacity of Li-ion batteries (LIBs), but they still suffer from poor cycling and rate performances due to their serious self-aggregation and pulverization. Constructing micro/nano-structures is a quite promising method to address the above issues. However, it remains a huge challenge to build 3D hierarchical porous micro/nano-structures self-assembled from ultrathin nanostructured building blocks, which has prompted extensively great interest. Herein, we report a facile “hydrolysis–controllable crystallization” strategy to controllably synthesize different dimensional (i.e. 1D, 2D, and 3D) VO2 (B) nanostructures by a simple one-step high-temperature mixing method under hydrothermal conditions. In particular, unique 3D micro/nano-structured hierarchical porous sponge-like micro-bundles (SLMBs) self-assembled from 2D crumpled ultrathin VO2 (B)@C nanosheets with a thickness of only ∼3.1 nm (denoted as VO2 (B)@C-SLMBs) are synthesized. This is the first report on the synthesis of 2D ultrathin VO2 (B) nanomaterials. Importantly, the intrinsic VO2 (B) crystallization behavior and controllable synthesis mechanism of VO2 (B) micro/nano-structures are revealed for the first time by the density functional theory calculation. The as-synthesized VO2 (B)@C-SLMBs possess distinct structural advantages, i.e., large surface area, abundant meso/micropores, robust structure and conductive carbon frameworks, which make them exhibit excellent electrochemical performance in terms of long life, high rate, and large capacity as cathode materials of LIBs. The discharge capacity was 206 mA h g−1 after 160 cycles at 100 mA g−1, corresponding to 105% of the initial capacity. Even at a large current density of 1000 mA g−1, they still exhibit a high retention of 104% after long period of 1000 cycles. These results indicate that the as-synthesized VO2 (B)@C-SLMBs have a great potential for long-life and high-rate cathode materials of next-generation LIBs.

Nanomaterials, especially graphene-like 2D ultrathin ones that possess a wealth of unprecedented functionalities, can increase the discharge capacity of Li-ion batteries (LIBs), but they still suffer from poor cycling and rate performances due to their serious self-aggregation and pulverization. Constructing micro/nano-structures is a quite promising method to address the above issues. However, it remains a huge challenge to build 3D hierarchical porous micro/nano-structures self-assembled from ultrathin nanostructured building blocks, which has prompted extensively great interest. Herein, we report a facile “hydrolysis–controllable crystallization” strategy to controllably synthesize different dimensional (i.e. 1D, 2D, and 3D) VO2 (B) nanostructures by a simple one-step high-temperature mixing method under hydrothermal conditions. In particular, unique 3D micro/nano-structured hierarchical porous sponge-like micro-bundles (SLMBs) self-assembled from 2D crumpled ultrathin VO2 (B)@C nanosheets with a thickness of only ∼3.1 nm (denoted as VO2 (B)@C-SLMBs) are synthesized. This is the first report on the synthesis of 2D ultrathin VO2 (B) nanomaterials. Importantly, the intrinsic VO2 (B) crystallization behavior and controllable synthesis mechanism of VO2 (B) micro/nano-structures are revealed for the first time by the density functional theory calculation. The as-synthesized VO2 (B)@C-SLMBs possess distinct structural advantages, i.e., large surface area, abundant meso/micropores, robust structure and conductive carbon frameworks, which make them exhibit excellent electrochemical performance in terms of long life, high rate, and large capacity as cathode materials of LIBs. The discharge capacity was 206 mA h g−1 after 160 cycles at 100 mA g−1, corresponding to 105% of the initial capacity. Even at a large current density of 1000 mA g−1, they still exhibit a high retention of 104% after long period of 1000 cycles. These results indicate that the as-synthesized VO2 (B)@C-SLMBs have a great potential for long-life and high-rate cathode materials of next-generation LIBs.

A remarkably simple and effective high-temperature mixing method under hydrothermal conditions was applied to synthesize well-crystallized V3O7·H2O nanobelts, VO2 (B) nanosheets and VO2 (A) nanorods with good performances for Li-ion batteries. In particular, V3O7·H2O exhibited an excellent electrochemical performance. The outstanding electrochemical properties were explained through analysis of the crystal structures.

Structural modification, especially the stabilization of metastable phases at room temperature, has emerged as an effective strategy to understand their stabilization mechanism and improve their functional properties. In this work, a facile solvothermal approach is developed to synthesize metastable sodium niobate (NaNbO3) crystals with the cubic symmetry. XRD, Raman and TEM results all confirmed the selective synthesis of cubic and orthorhombic NaNbO3via adjustment of the reaction medium. The fact that traditional hydrothermal synthesis often yields orthorhombic NaNbO3 inspires us to elucidate the formation mechanism of cubic NaNbO3 with respect to the solvent effect. With the increasing post-calcination temperature, the as-synthesized cubic NaNbO3 gradually transforms into the orthorhombic structure, which is understood to be a recrystallization behavior, as evidenced by the XRD and TEM results. The organic molecules retained in the NaNbO3 nanocrystals, as suggested by UV-vis, FT-IR and TGA-MS results, have contributed to the stabilization of the metastable structure, demonstrated by the different temperature-induced phase transition behaviors in air and argon atmospheres, where the phase transition from cubic to orthorhombic would take place at a relatively higher temperature in argon. This work provides an alternative approach to synthesize cubic NaNbO3 nanocrystals, and the understanding of the stabilization mechanism could pave a new pathway for fabricating metastable materials.