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We report the structure, dielectric, ferroelectric and piezoelectric properties of Cr-Mn co-doped (1-y)BiFe1-xCrxO3-yBaTi1-xMnxO3 (0≤x≤0.04, 0.2≤y≤0.27) ceramics. By varying both x and y, a series of samples near morphotropic phase boundaries exhibiting both high ferroelectric Curie temperature TC (∼580−643 °C) and relatively large piezoelectric constant d33 are constructed. Especially, the sample with y = 0.24 and x = 0.02 is found to show coexistence of high depolarization temperature Td (∼551 °C) and relatively large d33∼116 pC/N, superior to most of those of BiFeO3 based high-temperature piezoceramics reported previously. The enhanced ferroelectric TC in the Cr-Mn modified samples can be ascribed to the combined effects of large lattice distortion and high tetragonal phase content. These results demonstrate that constructing morphotropic phase boundaries via considering simultaneously the role of lattice distortion might be effective route to realize high-temperature and high piezoelectricity in BiFeO3-based systems.

Transparent conducting (TC) donor-doped In2O3 thin films are the critical components in photovoltaic, display and solid-state lighting fields. In2O3-based TC films with high carrier mobility are required for reducing the power consumption of devices. Meanwhile, a high near-infrared (NIR) transparency can significantly improve the power conversion efficiency in solar cells. Here, W-doped In2O3 thin films with high carrier mobility and NIR transparency were obtained through a facile solution process, which is suitable for large-scale thin film fabrication. The effects of W concentration (0.3 at% to 0.7 at%) on the microstructures, electrical and optical properties of In2O3 thin films are investigated in detail. It is found that the 0.5% W-doped In2O3 thin film exhibits high carrier mobility of 23 cm2 V−1 s−1 at a carrier concentration of 5.02 × 1020 cm−3, showing a high NIR transmittance over 82% and low sheet resistance of 32 Ω/sq. The solution processed W-doped In2O3 thin films with low sheet resistance and high NIR transparency can be potentially used as transparent electrodes for solar cells.

The structural, magnetic, dielectric and optical properties of Aurivillius Bi6Fe2Ti3O18-based ceramics were investigated in detail. The replacement of Co for Fe/Ti ions obviously varies the grain morphology. Compared with Bi6Fe2Ti3O18 (BFTO) with antiferromagnetic ordering, a spin glass state can be observed in Bi5.25La0.75Fe2Ti3O18 ceramic, while other samples exhibit the ferromagnetic behavior. The specimen Bi6Fe2Ti2(NbCo)0.5O18 (BFTNCO) represents the largest remanent magnetization Mr of 0.93emu/g among all the samples, which can be attributed to the combination of a short lattice parameter c and a large lattice distortion as well as more magnetic ions in a unit cell. The room-temperature dc conductivity of BFTNCO is one order magnitude lower than that of BFTO. In addition, the band gaps of Co-doped samples are about 0.2eV smaller than these of Co-free samples. This work provides a promising path forward to tailor the multiferroic and optical properties in five-layered Aurivillius compounds.

Two-dimensional MXenes (such as Ti2C, V2C, Nb2C, Ti3C2, and Nb4C3) have shown enormous potential in lithium ion storage, and the exploration of new and/or high- performance MXene-based lithium ion storage materials is an active field. This present work demonstrates the synthesis of two-dimensional vanadium carbide V4C3 MXene by selectively etching Al layers from V4AlC3 in hydrofluoric acid at 55 °C. Large specific surface (∼52.1 m2 g−1) and interlayer spacing (∼0.466 nm) can be obtained in V4C3 MXene via adding sufficient ball-milling treatment on precursor V4AlC3, which is benefit for lithium ion storage. As an anode material for lithium ion batteries, it shows high capacity as well as good rate capability and cycling performance. More specifically, V4C3 delivers a high specific capacity of 225 mAh g−1 after 300 charge/discharge cycles at a current density of 0.1 A g−1, and 125 mAh g−1 at 1 A g−1. This work provides another potential MXene-based lithium ion storage material and is expected to inspire more explorations of high-performance MXene-based electrode materials for lithium ion batteries and capacitors.

Columnar nanostructures or ordered nanoarrays of CoFe2O4 (CFO) thin films are desirable in applications. While, the difficulties in achieving large-area columnar CFO thin films with a tunable lateral size and a controllable height/length ratio have limited their applications as synthesizing heterostructures and composites. Herein, CFO thin films with vertically aligned nanorod structures from bottom to up have been achieved on silicon substrates by high magnetic field assisted pulsed laser deposition. Lateral size of the nanorod decreases with increasing the magnetic field. Moreover, both the coercivity and the magnetization at room temperature increase with increasing the magnetic field in deposition. These results will provide a feasible route to deposit large-area and technologically relevant to advance the applications of CFO thin films.

The present work reports oxygen evolution reaction (OER) activity in metallic V4AlC3 bulk powders prepared by solid-state reactions for the first time. An ultralow overpotential of 253 mV at the current density of 10 mA cm−2 and an excellent stability are observed, demonstrating that V4AlC3 bulk powder can be used as an excellent new type of OER catalyst with low-cost for mass production.

Two-dimensional (2D) MXenes such as Ti3C2, Ti2C, Mo2C, and Mo1.33C have shown excellent electrochemical performances as supercapacitor electrodes, and the exploration of new and/or high-capacity MXene-based supercapacitor electrode materials is an active field. In this work, 2D multi-layered V4C3 MXene has been synthesized by selectively etching Al from V4AlC3 and it shows a high capacitance of 209 F g−1 at 2 mV s−1, good rate performance, and stable long cyclic performance with capacitance retention rate of 97.23% after 10000 cycles at 10 A g−1 in 1 M H2SO4. Importantly, the pseudocapacitance (∼100.1 F g−1) accounts for about 37% of the total capacity (∼268.5 F g−1) for V4C3 MXene electrode. Therefore, the high specific capacitance of V4C3 MXene is not only due to their wide interlayer spacing (∼0.466 nm), large specific surface areas (∼31.35 m2 g−1) and pore volumes (∼0.047 cm3 g−1), and good hydrophilicity but also attributed to the abundant valence states of vanadium (+2, +3, and +4). The high rate performance and excellent cycling stability of V4C3 MXene electrodes are mainly attributed to the high electronic conductivity (1137 S m−1 at 300 K). The present work provides another promising MXene-based supercapacitor electrode material.

A couple of layered Li-rich cathode materials Li1.2Mn0.54Ni0.13Co0.13O2 without any carbon modification are successfully synthesized by solvothermal and hydrothermal methods followed by a calcination process. The sample synthesized by the solvothermal method (S-NCM) possesses more homogenous microstructure, lower cation mixing degree and more oxygen vacancies on the surface, compared to the sample prepared by the hydrothermal method (H-NCM). The S-NCM sample exhibits much better cycling performance, higher discharge capacity and more excellent rate performance than H-NCM. At 0.2 C rate, the S-NCM sample delivers a much higher initial discharge capacity of 292.3 mAh g−1 and the capacity maintains 235 mAh g−1 after 150 cycles (80.4% retention), whereas the corresponding capacity values are only 269.2 and 108.5 mAh g−1 (40.3% retention) for the H-NCM sample. The S-NCM sample also shows the higher rate performance with discharge capacity of 118.3 mAh g−1 even at a high rate of 10 C, superior to that (46.5 mAh g−1) of the H-NCM sample. The superior electrochemical performance of the S-NCM sample can be ascribed to its well-ordered structure, much larger specific surface area and much more oxygen vacancies located on the surface.

Porous thin films showing improved physicochemical properties are desirable. Here, we developed a facile route, laser-assisted chemical solution deposition (LACSD), to deposit porous Fe3O4 thin films. The synthesized porous Fe3O4 thin films show excellent electrochemical performance as anodes in lithium ion batteries. The results will provide a facile route to synthesize porous large-area metal oxide thin films.

A new type of Zn2VO4/ZnO/carbon composite (three-dimensional porous architecture) was firstly fabricated on a Ni-metal foam substrate thorough a facile electrostatic spray deposition (ESD) method followed by a calcination process. As a binder-free electrode in high performance lithium-ion batteries (LIBs), the composite electrode displays an outstanding long cycling performance, and it exhibits a high specific capacity of 930.8 mAh g−1 at 2 A g−1 even after 800 cycles without any capacity fading. And, the composite also shows a good rate performance with specific charge capacities of 742.1, 658.7, 804.9, 567.3 and 519.3 mAh g−1 at 0.1, 2, 5, 10 and 12 A g−1, respectively.

NH3 annealing effects on V4C3Tx MXene have been investigated. The nitrogen concentration varies with the annealing temperatures. Through the ammonia treatment at 350 °C (NH3-V4C3Tx-350 °C), nitrogen atoms can incorporate into V4C3Tx MXene, leading to a loss of F. The NH3-V4C3Tx-350 °C electrodes exhibit a higher specific capacitance of 210 F g−1 than that of the pristine V4C3Tx at the scan rate of 10 mV s−1 in 1 M H2SO4. Additionally, superior rate performance and excellent cycling stability are demonstrated. This new type of nitrogen-doped V4C3Tx could be a promising electrode material for high-performance supercapacitors.

MnF2 particles with the average size of around 26 nm have been prepared successfully with NH4HF2 as a fluorine source by a simple solvothermal method. Compared with previous reports, as-prepared MnF2 shows evidently improved cycle performance with a high reversible capability 481.9 mAh g−1 at 0.1 C for the first cycle and stable discharge capability 530.5 mAh g−1 and 359.2 mAh g−1 at 0.1 C and 1 C for 250 cycles respectively, which indicates its promising application as anode for lithium-ion batteries.

The effects of Co ions substitution on the structural, multiferroic, dielectric, and optical properties of Aurivillius Bi5FeTi3O15 are investigated. High resolution transmission electron microscope measurements imply that Bi5FeTi2Nb0.5Co0.5O15 (BFTNCO) exhibits a typical four-layered Aurivillius structure. The co-doping of Nb/Co ions at Ti sites is found to induce the lattice distortion. In comparison with Bi5FeTi3O15 and Bi5Fe0.5Co0.5Ti3O15, the sample BFTNCO shows a more superior multiferroicity with the remanent magnetization Mr and polarization Pr of 76.4 memu/g and 10.2 μC/cm2, respectively. The improved multiferroicity can be ascribed to reduced oxygen vacancy, large lattice distortion and large grain size. In addition, a relatively narrow optical band gap Eg can be obtained as 2.30 eV for BFTNCO. The decreased Eg in BFTNCO can be attributed to large lattice distortion and the overlap of Co 3d state with Ti t2g state. These results reveal that Ti-site doped Aurivillius phase may be the potential candidates for exploring excellent room-temperature multiferroics with narrow band gap.

Na-doped lithium vanadates Li3−xNaxVO4 (x = 0, 0.03, 0.05, and 0.08) were synthesized as anode materials for lithium-ion batteries by a simple sol-gel method. The structural and morphological characterizations reveal that Na-doping in Li3VO4 leads to slightly expanded lattice and suppressed particle agglomeration with relative uniform morphology and the doped Na+ ions distributed uniformly throughout Li3VO4 grains. The Na-doped Li3VO4 electrodes present enhanced cycling stability, better rate performance and lower charge transfer resistance, especially for the Li2.95Na0.05VO4 electrode. It delivers the highest initial charge capacity of 523.4 mAh/g at 0.1C in the series electrodes. After 150 cycles at 1C, Li2.95Na0.05VO4 electrode maintains a charge capacity of 398.3 mAh/g, which is almost the same with that of the initial one. In addition, Li2.95Na0.05VO4 electrode also exhibits a much better rate capability with 364 and 284 mAh/g at 2C and 4C, respectively, superior to that of Li3VO4. The excellent electrochemical performance of the Na-doped samples is suggested to originate from the much higher lithium diffusion coefficient induced by the expanded lattice, the much smaller polarization and charge transfer resistance.

Chemical solution deposition is used to prepare Co5.47N thin films on LaAlO3 single crystal substrates. The derived thin films are phase-pure and polycrystalline. Annealing temperature effects on microstructures, magnetic and transport properties are investigated. The thin films annealed under 800 and 900 °C shows dense surface morphologies, whereas the 1000 °C annealing temperature will lead to dewetting. The derived Co5.47N thin films are ferromagnetic with Curie temperature higher than 632 K. The room-temperature saturation magnetization is enhanced and the coercivity is decreased with increasing the annealing temperature from 800 to 1000 °C. The temperature dependent resistivity shows metallic behaviors, and it is decreased with increasing the annealing temperature. The results will provide a facile route to prepare Co5.47N thin films using chemical solution deposition.

The structural, magnetic and dielectric properties of tungsten bronze Ba4Nd2Fe2-xCoxNb8O30 (0 ≤ x ≤ 1) ceramics are investigated. The room-temperature ferromagnetic (FM) behavior with rather high FM transition temperature Tc can be observed in the Co-doped samples compared with the antiferromagnetic (AFM) interaction in the sample Ba4Nd2Fe2Nb8O30. The ferromagnetism can be understood in terms of spin canting of the AFM coupling of the Fe-based and Co-based sublattices via Dzyaloshinsky-Moriya interaction. All the samples exhibit the nature of relaxor ferroelectric. In addition, two thermally activated dielectric relaxations can be found in all the samples. The first one corresponds to a relaxor-like relaxation which obeys well Vogel-Fulcher relation, whereas the second one follows with Arrhenius Law and can be attributed to the localized hopping of electrons.

Bi7Fe3−xNixTi3O21 thin films were prepared by chemical solution deposition on Pt/Ti/SiO2/Si substrates. The Ni doping effects on the dielectric, leakage, ferroelectric and magnetic properties were investigated. Coexistence of ferroelectric and ferromagnetic properties at room-temperature was observed in the Bi7Fe2NiTi3O21 thin film with a remnant polarization 2Pr of 36.4 μC/cm2 and a remnant magnetization 2Mr of 3.9 emu/cm3. The dielectric and leakage properties were discussed in detailed. The results will provide important information to explore single-phase multiferroic materials.

The structural, multiferroic, dielectric, and magneto-dielectric (MD) properties of Aurivillius Bi7Fe2CrTi3O21 ceramic are investigated in detail. The sample shows a dominant antiferromagnetic state with the existence of weak ferromagnetic ordering. The saturation magnetization Ms and remnant polarization Pr are 2.85 emu/g and 4.1 μC/cm2, respectively. The results of dielectric, electrical modulus, impedance and scaling behavior indicate that the dielectric relaxation is induced by the localized hopping process of electrons. In addition, the MD property in low frequency range can be ascribed to the extrinsic effect stemming from grain boundary relaxation, whereas the MD property in high frequency region can be attributed to the intrinsic effect arising from grain relaxation. More importantly, a relatively large intrinsic magneto-dielectric constant of −1.27% can be achieved at 1 MHz and 300 K. These results imply that Cr-doped Aurivillius compounds may be the potential candidates for MD applications.

In this work, solution derived Aurivillius Bi7Fe2NiTi3O21 (BFNTO) thin films were prepared by in-situ magnetic annealing. The evolution of structure, ferroelectric and magnetic properties were systematically studied. As the increase of annealing magnetic field to 4 Tesla, the ferroelectric properties were improved with a larger intrinsic remnant polarization of 12.4 μC/cm2. The magnetic properties were substantially improved with remnant magnetization from 1.4 to 3.2 emu/cm3 as the annealing magnetic field increases from 0 to 6 Tesla. These results indicate that in-situ magnetic annealing is an effective method to optimize ferroelectric and magnetic properties of multiferroics.

Considering the atomic size mismatch between Mo and W, a large compressive microstrain is introduced and phase engineering may be achieved in MoS2. A simple one-step hydrothermal method as a facile method is employed to synthesize 1T-Mo0.71W0.29S2. 1T-Mo0.71W0.29S2 doping Co element and then growing on carbon cloth are the effective way to improve the supercapacitor performance. Benefitting from the outstanding conductivity of 1T-Mo0.71W0.29S2 and carbon cloth, the more active sites by doping Co, the electrode of Co-(1T-Mo0.71W0.29S2)-1% on carbon cloth exhibits high specific capacity of 1235 mF cm−2 at 2 mA cm−2. Flexible symmetric supercapacitors constructed by Co-(1T-Mo0.71W0.29S2)-1% on carbon cloth show high energy density (22.7 μWh cm−2), strong flexibility and stability (88.7% at 20 mA cm−2). The simple strategy provides a facile route for easy phase engineering and improvement on performance of transition metal dichalcogenides (TMDs).

Transition metal nitrides are of great interest for lithium storage application due to their high electrical conductivity and low voltage plateau. However, the relative cycling stability restricts their practical application. Herein, a stable bimetal nitride NiCo2N hollow sphere material with interconnected nanosheets shell was successfully synthesized via a facial solvothermal route. When used as anodes for lithium-ion batteries, the unique structure can effectively relieve the volume change of the electrode material, and shorten the diffusion distance of lithium ions during the repeated cycling processes. As a result, the NiCo2N electrode exhibits an excellent electrochemical performance. It delivers high discharge capacity of 1244.5 mAh g−1 at a current density of 1 A g−1 after 400 cycles, the capacity can maintain 529.4 mAh g−1 at high current density of 5 A g−1. Furthermore, the electrochemical reaction mechanism of the electrodes is revealed by ex situ XRD, ex situ EIS, and ex situ HRTEM characterization.

Epitaxial La0.5Ca0.5MnO3 (LCMO) thin films with vertically aligned nanostructures (VANs) have been achieved with the application of high magnetic fields in pulsed laser deposition processing. More interestingly, the microstructures, vertical strain, and perpendicular magnetic anisotropy (PMA) in the LCMO VAN films can be systematically manipulated by changing the applied high magnetic field strength. With increasing the high magnetic field, an increase in growth rate and a decrease in nanocolumn dimension are observed in the LCMO VAN films, which can be attributed to the enhanced suppression effect on adatom mobility and surface diffusion. Different from the LCMO planar-structured films, the intrinsic stress behaviors associated with vertical interfaces and grain boundaries instead of substrate strain in the LCMO VAN films are dominant in vertical strain evolution, indicating an out-of-plane compressive state, which is highly correlated with the growth rate and nanocolumn dimension. A core-shell model based on phase separation is proposed to understand the nanoscale size effect on magnetic properties in the LCMO VAN films. A tunable and enhanced PMA effect in the LCMO VAN films is also demonstrated. The results suggest that the application of a high magnetic field in pulsed laser deposition processing is a practicable route to achieve tunable VANs, and manipulate physical properties in manganite films.

We investigate the structural, magnetic, and dielectric properties of Aurivillius Bi 5 FeTi 3-3 x (WCr 2 ) x O 15 (0 ≤ x ≤ 0.15) multiferroic ceramics. All the samples can be determined to be an orthorhombic structure and space group of A2 1 am . The magnetic measurements reveal that the short-range antiferromagnetic exchange interaction can be strengthened by doping Cr 3+ ions at Ti sites. The ferroelectric Curie temperature T c decreases from 1013 K to 965 K. One dielectric relaxation dates from the long-range motion of oxygen vacancies can be observed in all the samples. However, the doped samples exhibit another one dielectric relaxation, which is relate to the localized hopping process of electrons. In addition, the dc conduction behavior in all the samples can be attributed to the long-range motion of oxygen vacancies.

Co-Fe alloy thin films with high magnetization are desirable in numerous applications. Co-Fe thin films prepared by solution methods with refined microstructures have not been achieved up to now. Here, high magnetic field annealing (HMFA) is introduced for the preparation of Co 70 Fe 30 alloy thin films. The effects of HMFA on their microstructures and room temperature magnetic properties are investigated. The thickness of the derived Co 70 Fe 30 thin films is dramatically decreased from a value of 590 nm without HMFA to 320 nm with 7 T magnetic field annealing, and the refinement of microstructures is also observed with HMFA. The derived Co 70 Fe 30 film annealed under 7 T magnetic field exhibits a saturation magnetization of ∼ 2.43 T, close to the theoretical value of 2.45 T. Overall, HMFA provides a feasible way to fabricate larger-area and denser Co-Fe thin films with excellent magnetic properties.

MnO/reduced graphite oxide (MnO/RGO) composite films with three dimensionally porous structures have been synthesized by an improved electrostatic spray deposition setup and their microstructure and electrochemical properties have been characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric, Raman spectrometry and galvanostatic cell cycling. The results show that the structure and electrochemical performance of the electrode film are influenced significantly by the RGO content. The three dimensionally porous structure collapse does not occur in the MnO/RGO thin films for a RGO content lower than 16.58 wt%, the 16.58 wt% reduced graphite oxide content being optimal. Such an improvement in the cycling performance (772 mAh g −1 after 100 cycles at 1 C) and rate capability (425 mAh g −1 at 6 C) might be attributed to the excellent microstructure and electrical conductivity of MnO/reduced graphite oxide composite film electrodes.

Molybdenum nitrides Mo-N are considered as the hardest superconducting metal nitrides, which are usually prepared under high pressure and high temperature to obtain high superconducting transition temperature T c . Here, polycrystalline δ -MoN thin films with self-assembled c -axis orientation are directly deposited onto Si substrates by chemical solution deposition under ambient NH 3 annealing atmosphere without high pressure processing. The prepared δ -MoN/Si thin films show T c higher than 12 K. The normal state resistivity obeys electron-phonon scattering mechanism and can be well fitted by Bloch-Gruneisen expression. The results will provide an effective route to prepare large-area δ -MoN/Si thin films with high T c as well as a guidance to investigate the fundamental properties of polycrystalline δ -MoN thin films.