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Improving the properties of activated carbon (AC) electrodes for enhancing the electrochemical performance of commercial supercapacitors is still a great challenge. In this work, a coconut shell ca...

The electrical conductivity of ferroelectric-ferromagnetic ceramic composites usually increases monotonously with elevated temperature, which may seriously deteriorate their performance. In this work, we report an anomalous conductivity behavior induced by in situ metastable amorphous phase in a semi-conductive ceramic composite, 0.1BaTiO3(BTO)/0.9Ni0.5Zn0.5Fe2O4(NZFO). The ceramic composites with in situ formed amorphous BTO phase (a-BTO) or crystalline BTO phase (c-BTO) were successfully prepared. The effect of such metastable amorphous phase on the electrical transport properties of the ceramic composite was investigated. A comparative study reveals that a-BTO could act as a buffering phase preventing the electrical conductivity of the composite from monotonous increment above a critical temperature (513 K), whereas such effect does not occur when BTO is pure crystalline. Around 513 K, a change in the activation energy of dc conductivity has been observed for the c-BTO/NZFO sample. Whereas for the a-BTO/NZFO sample, the Arrhenius relation fails to describe its behavior above 513 K owing to decreased conductivity, which is rarely seen in semiconductors. The activation energy of relaxation is identical for both systems, i.e. 0.204 eV, because their dielectric relaxation is dominated by crystalline NZFO phase. The findings of this work are inspiring for the design of novel electronic materials constituted by a crystalline phase and an amorphous phase with adjustable performance.

In order to prepare calcium carbonate nanoparticles in a green and environmentally friendly way, the concept of bio-mineralization has been proposed. Glucose, as a common small molecular organic substance found in organisms, participates in the mineralization process in cells. By adding glucose as a chemical additive, long chains of calcium carbonate form at the initial stage and then break granularly

A larger liquid–gas interface area during the carbonation process for preparing high-purity aragonite CaCO3 whiskers by using porous quartz stones was developed. The presence of plenty of open pores ranging from 0.02 to 0.20 mm inside the porous quartz stones could disperse CO2 gas in Ca(OH)2 suspension into tiny bubbles, with an average diameter ranging from 0.28 to 3.05 mm and a large liquid–gas interface area ranging from 3571.4 to 327.9 mm2, respectively, which could enhance the diffusion effect of CO2 molecules and the uniformity of carbonate ions in the system. Thus, a uniform and low supersaturation was obtained, improving the growth of CaCO3 whiskers. The prepared CaCO3 whiskers showed the highest purity of 99.7%. The formation mechanism of ultrahigh purity CaCO3 whiskers was also studied in detail. Then, the prepared CaCO3 whiskers were introduced into a PVC matrix to study their effect on the tensile strength of PVC, and the results showed that the tensile strength was enhanced by 46.4% with 5 wt% whiskers. This method provides an effective way to enhance the performance of inorganic crystals.

A Schottky barrier is a double-edged sword in electronic and optoelectronic devices, especially devices based on two-dimensional materials. It may restrict the carrier transport in devices, but it can also realize multifunctional devices by architecture design. We designed a simple but novel device structure based on theWSe2-Cr Schottky junction with an asymmetric Schottky contact area of the source and drain. A significant rectification ratio over 105 and multiple rectifying states (e.g., full pass, forward pass, off, and backward pass) were achieved in the single Schottky junction tuned by gate voltage. Furthermore, switching characteristic, rectification characteristic, and amplitude of a sin wave can be effectively modulated by the electrical field or light illumination in a signal process circuit based on the WSe2-Cr Schottky junction. The highly tunable Schottky junction working as a multimode signal processor unit has great potential in future optoelectronic-integrated chips.

Novel 1–3 type multiferroic composite thin films were prepared via a simple 0–3 composite fabrication process. The orientation of the Ni0.5Zn0.5Fe2O4 (NZFO) nanocrystals in the BaTiO3–Ni0.5Zn0.5Fe2O4 (BTO–NZFO) composite thin films was controlled by magnetron sputtering, and the controlling effect of such orientation on magnetoelectric coupling was investigated in detail. The NZFO lattice in the BTO–NZFO composite thin films grew with (100) orientation under the induction of the (111) plane of Si. The transfer of substrate stress between the closely contacted grains also contributes to the orientation of the NZFO nanocrystals. The 0.6BTO–0.4(100)NZFO multiferroic composite thin film exhibited a magnetization strength of 9.2% at the Curie point of the BTO phase, showing extremely strong magnetoelectric coupling characteristics. This work provides an effective strategy for the development of high-performance multiferroic composites, and brings about new conception of realizing strong magnetoelectric coupling effect from the perspective of physical chemistry.

A hyperelastic percolative conductive composite is proposed with acetylene black (AB) as conductive filler introduced into Ecoflex® 00-30 elastomer matrix. The conductivity could be enhanced by several orders according to percolation theory and the Young’s modulus could also be tailored by modifying AB volume ratio. The AB-Ecoflex composite exhibits electric conductivity high as 6.4 S·m−1 and remains stable after 100 cycles at 200% strain. This composite with high conductivity, stretchability and stability shows high potential as a competitive candidate for wearable strain sensors to detect human body motions and for human-machine interface application.

High dielectric and magnetic properties coexisted in one is important for the miniaturization and multifunction of electronic devices. Ni doped barium ferrites were successfully fabricated by sol-gel technique in this work. The microstructures and properties were investigated by the means of XRD, SEM, XPS, impedance analysis and magnetic property measurement systems. Results showed that main phase of M-type barium ferrite with hexagonal plate-like grains and Ni 2+ ions substituting for Fe 3+ as BaFe 12-x Ni x O 19 was formed. Ni 2+ doping promotes the formation and grain growth of barium ferrite ceramics. The optimized sintering temperature was 1250 °C at which relatively perfect microstructure was formed. Giant permittivity above 20 k and low dielectric loss of ∼0.1 generated in the ferrite. Low H a of 14–13 kOe and H c of 145–111 Oe emerged and large saturation magnetization of 60–72 emu/g presented in Ni 2+ -doped barium ferrites ceramics. The coexistence of impressive dielectric and magnetic properties in Ni 2+ -doped barium ferrites ceramics, makes it potential candidate in the area of miniaturization and multifunction of electronic devices.

A facile, low-cost magnetic field-assisted chemical reduction method was proposed for synthesizing nickel nanowires (NiNWs) with both controllable diameter and high length to diameter (L/D) ratio at temperature as low as 60 °C. NiNWs with diameter as low as 180 ± 21 nm and L/D ratio as high as 300 were achieved by controlling the reaction temperature, NiCl2 concentration and the quantity of reductant in a magnetic field of 170 mT. Based on the NiNWs, a high-sensitivity and stretchable strain sensor with sandwich structure consisting of NiNWs and Ecoflex elastomer was proposed. Gauge factor as high as 200 was demonstrated up to a strain of 100%. Applications of the sensor in detecting body motion including finger gestures, facial expressions and different phonations are presented. This study provides a promising solution for smart sensors for next generation robotics as well as for human–machine interfacing applications.

WSe2 has attracted extensive attention for p-FETs due to its air stability and high mobility. However, the Fermi level of WSe2 is close to the middle of the band gap, which will induce a high contact resistance with metals and thus limit the field effect mobility. In this case, a high work voltage is always required to achieve a large ON/OFF ratio. Herein, a stable WSe2 p-doping technique of coating using a ferroelectric relaxor polymer P(VDF-TrFE-CFE) is proposed. Unlike other doping methods, P(VDF-TrFE-CFE) not only can modify the Fermi level of WSe2 but can also act as a high-k gate dielectric in an FET. Dramatic enhancement of the field effect hole mobility from 27 to 170 cm2 V-1 s-1 on a six-layer WSe2 FET has been achieved. Moreover, an FET device based on bilayer WSe2 with P(VDF-TrFE-CFE) as the top gate dielectric is fabricated, which exhibits high p-type performance over a low top gate voltage range. Furthermore, low-temperature experiments reveal the influence of the phase transition of P(VDF-TrFE-CFE) on the channel carrier density and mobility. With a decrease in temperature, field effect hole mobility increases and approaches up to 900 cm2 V-1 s-1 at 200 K. The combination of the p-doping and gating with P(VDF-TrFE-CFE) provides a promising solution for obtaining high-performance p-FET with 2D semiconductors.

Development of high-efficiency millimeter-wave-absorbing materials is important to attenuate electromagnetic pollution occurring due to rapid development of information technology and to defend against radar detection for military stealth technology. In this study, BaTiO3 (BTO)/Co3O4 millimeter-wave absorption composite powders with hierarchical microstructures were successfully prepared by the sol–gel method. The results indicated that the Co3O4 phase was preferentially formed at low temperature of 800–900 °C and BTO was formed at high temperature of 1000–1100 °C. A composite with perfect crystallization of both constituent phases and uniform microstructure was obtained when its molar ratio of BTO/Co approached 1 and the sintering temperature was around 900 °C. Both permittivity and permeability resonances were generated typically in composites, due to which er and μr values were relatively closer and e′′ and μ′′ were high at high-frequency range of 30–40 GHz. In the composite with molar ratio of BTO/Co of 4/6 sintered at 900 °C, double absorption peaks with appropriate frequency difference were generated, and absorption intensity from −40 to −50 dB and bandwidth of 5 GHz were successfully obtained with sample matching thickness of 1.8 mm around 35 GHz. It completely covered the atmosphere window at 35 GHz, which has the strongest transparency of millimeter wave. This composite can be used as a highly efficient absorption material of millimeter-wave rays.

For a new breakthrough of highly efficient magnetoelectric (ME) coupling of multiferroic composite thin film in application of next generation multifunctional devices, it is important to control constituent magnetic phase pillar array independently embedded inside piezoelectric phase. In this work, in situ spin-coated xNi0.5Zn0.5Fe2O4/(1-x)BaTiO3 composite thin films on Si substrate with high magnetoelectric coupling are successfully obtained via phase separation. Results show that hexagonal Ni0.5Zn0.5Fe2O4 (NZFO) grain grows (111)-oriented as single crystal pillars arrayed independently uniformly and surrounded by BaTiO3 (BTO) phase. Ti and Fe ions are doped into the NZFO and BTO phases respectively and decreased with the decrease in corresponding constituent phases. Grain size and lattice constant of the cubic NZFO are from ~1 to ~0.5 μ m and from 0.8383 nm to 0.8369 nm respectively in terms of x. The orientation degree of thin films is> 56% when x is above 0.8. The 0.8NZFO/0.2BTO thin film with and without pure BTO after-spincoated shows giant ME coupling effect, about 40% change of magnetization of NZFO in terms of phase transition of ferroelectric BTO at Curie temperature ~398 K. It is much larger than others on Si substrate ever reported and may be applied cost-effectively, coupling-efficiently and widely in Si-based chips area.

A highly transparent and flexible percolative composite with magnetic reduced graphene oxide@nickel nanowire (mGN) fillers in EcoFlex matrix is proposed as a sensing layer to fabricate high-performance flexible piezoresistive sensors. Large excluded volume and alignment of mGN fillers contribute to low percolation threshold (0.27 vol %) of mGN-EcoFlex composites, leading to high electrical conductivity of 0.003 S m-1, optical transmittance of 71.8%, and low Young's modulus of 122.8 kPa. Large-scale microdome templates for sensors are prepared by hot embossing technology cost-effectively and COMSOL Multiphysics is utilized to optimize the sensor performances. Piezoresistive sensors fabricated experimentally show superior average sensitivity of 1302.1 kPa-1 with a low device-to-device variation of 3.74%, which provides a new way to achieve transparent, highly sensitive, and large-scale electronic skin.

A Schottky barrier is a double-edged sword in electronic and optoelectronic devices, especially devices based on two-dimensional materials. It may restrict the carrier transport in devices, but it can also realize multifunctional devices by architecture design. We designed a simple but novel device structure based on theWSe

The drastic change of properties near the percolation threshold usually limits the practical applications of percolative composite materials. In this work, a tri-phase system, i.e. a BaTiO3 (BTO)/Ni0.5Zn0.5Fe2O4 (NZFO)/BaFe12O19 (BFO) ceramic composite, is proposed and investigated in detail. The BFO phase was in situ formed during a hybrid process of sol–gel and self-combustion methods. The content of the BFO phase could be tuned conveniently by controlling the preparation conditions. The as-prepared BTO/NZFO/BFO tri-phase composite exhibited unprecedented stable dielectric properties that were distinct from those of conventional percolative composites above the percolation threshold due to the existence of a third phase. When the volume fraction of the NZFO phase exceeds 55%, the electrical conductivity and effective permittivity of the composite remain at a stable value of about 10−5 S cm−1 and 10 000, respectively, which is almost independent of the composition. Such behavior is the result of the synergistic control effect of the percolation effect and specific phase composition in the system. It is evident that the stability of the dielectric properties of the composite is chiefly contributed by the introduction of the BFO phase. Meanwhile, the composite exhibited a relatively high permeability of ∼17 with 90% NZFO loading, and its saturated magnetization is larger than 73 emu g−1, approximately 95% of the pure NZFO phase. The finding of our BTO/NZFO/BFO tri-phase ceramic composite with stable giant permittivity and extremely high permeability paves a new way to solve the difficulty of property instability above the percolation threshold in the utilization of percolative materials.

Tunable materials have been extensively studied due to their potential applications in many electrical devices. High tunability has been practically achieved in a number of ferroelectric materials such as perovskite phases under usually high DC electric field of 10–100 kV/cm. In this work, single phased M-type barium ferrite ceramics with colossal permittivity accompanied by defect pair dipoles and giant tunability under super low DC bias were successfully prepared by the sol-gel method. Results show that Zr4+ ions substituted for Fe3+ in the spinel phase of ferrites. The concentration of Fe2+ increased from 37.23% to 43.22% and subsequently decreased to 36.72% with increasing Zr4+ ions from 0 to 0.1 and then continuously to 0.3, respectively. The highest content of Fe2+ was ∼43.22% and thus the maximum concentration of Fe2+/Fe3+ pair dipoles formed between Fe2+ generated and Fe3+ nearby appeared in the ferrites with Zr4+ doping of 0.1. Not only in Zr4+ doped ferrites but also in the ferrites with doping other high valent ions, Fe2+/Fe3+ pair dipoles formed and controlled permittivity. Giant permittivity of above 30 k appeared in the ferrites with Zr4+ content of 0.1–0.3 and was controlled by external bias to form tunability. The activation energy of modulation of defect pair dipoles was only ∼0.182 eV, which is 85% lower than 1.2 eV of traditional perovskite BaTiO3. High dielectric tunability of more than 65% with only a low DC electric field of

The Ag/BiFeO3 composite thin films were prepared by sol–gel technology on ITO/glass substrate. Most of the Ag+ ions were reduced to form Ag nanoparticles in the thin film. Some Ag+ ions were doped into the BiFeO3 lattice to replace Bi, forming Ag doped BiFeO3. The average size of the Ag nanoparticles is 4–8 nm. The dielectric constant of the BiFeO3 thin film sintered at 550 °C with the molar ratio of Ag/Fe of 0.2 was enhanced to 139, which was nearly twice as high as that of pure BiFeO3. The dielectric loss kept at a low value of 0.15. The composite thin film also showed a typical ferromagnetism with the saturation magnetization of 2.2 emu/cm3. The Ag/BiFeO3 composite thin film showed typical ferromagnetism and high permittivity simultaneously.

M-type barium ferrites with Nb5+–Ni2+ ions substituting for Fe3+ ions (BaFe12−2xNbxNixO19, BFNNO, x = 0–0.8) were prepared using the sol–gel method. The results show that barium ferrite with hexagonal plate-like grains is obtained in the samples with x = 0–0.8 sintered at 1350 °C for 3 h. The concentration of Fe2+ ions increases by ∼24% from 15.93% with x = 0 to 19.70% with x = 0.8. The anisotropic field Ha and coercive field Hc are adjusted freely from 15.75 kOe and 1.00 kOe to 6.04 kOe and 80 Oe with increasing x from 0 to 0.7–0.8, respectively. Meanwhile, the saturation magnetization, Ms, still maintains high values of >50 emu g−1. Multiple magnetic resonance peaks and two reflection loss (RL) peaks appear in BFNNO, which shift from >40 GHz to 40 GHz to

For the sol–gel-derived BaFe12−xNbxO19 (x = 0–0.6), coercivity (Hc) and saturation magnetization (Ms) vary from 3.53–0.85 kOe and 70.3–53.8 emu g−1 to 1.02–0.22 kOe and 69.6–59.5 emu g−1, respectively, with an increase in sintering temperature from 1250 °C to 1350 °C. Moreover, e′ and e′′ increase from 4.13–4.04 and 0.0049–0.0045 to 7.64–6.93 and 1.50–0.97 over 26.5–40 GHz, and the multi-resonance peaks in permeability shift from ∼40+ GHz to ∼27 GHz. The bandwidth (BW) and reflection loss peak intensity (RLp) are broadened and enhanced from 0.8 GHz and −10.3 dB of the sample with x = 0.2 sintered at 1250 °C under 0.92 mm to 11.9+ GHz and −54 dB, respectively, of the sample with x = 0.6 sintered at 1350 °C under 0.86 mm around a millimeter-wave atmospheric window of 35 GHz. The effects of Nb5+ content (x) and sintering temperature on grain size, phase compositions, formations of Fe2+ and oxygen vacancy, and thus on static magnetism and EM parameters are investigated. The correlations of multi-resonance permeability, enhanced permittivity, and the order of matching thickness with absorption properties are also discussed in detail.

A kaolinite-serine intercalation compound was synthesized via the guest displacement method. Serine molecules were intercalated into kaolinite to form kaolinite-serine through exchange between serine and the guest molecules ethylene glycol or water, which was inserted into the interlayer space of kaolinite beforehand. The thickness of kaolinite-serine particles decreased to 14 nm from 30 nm of raw kaolinite after intercalation. The interlayer distance of kaolinite reached approximately 1.13 nm after the intercalation of serine molecules. The serine molecules inserted in the interlayer space of kaolinite molecules were arranged in a flattened monolayer configuration and partially compressed into the tetragonal holes in the silicate layer. The activation energy Ea for releasing the pre-intercalated molecule before ultimate exchanging with serine determines the intercalation degree of serine into kaolinite. Higher Ea makes the expansion of kaolinite with pre-intercalated molecules more stable, which will facilitate the final intercalation of serine. The activation energy is 6.95 kJ/mol for ethylene glycol and 21.2 kJ/mol for water, respectively, resulting in serine intercalation degree of 45%, and 85% correspondingly. The kaolinite-serine intercalation compound is expected to be applied in the pharmaceutical and cosmetics fields.

Ag nanoparticles were formed in PbZr 0.52 Ti 0.48 O 3 (PZT) thin films by the sol–gel technique through two stage processes. In the first stage, Ag-Pb alloy particles formed in all film heat treated for different time from 1 min to 10 min. The average size of the particles increased from 0.16 μm to 0.43 μm while the mole ratio of Pb/(Pb + Ag) in the alloy particles increased from 0.7% to 27%. After that in the second stage with the heat treatment time above 10 min, the lead rich Ag-Pb alloy particles started to decompose gradually. The silver nanoparticles formed in the thin film to form nano-Ag/PZT composite. The number of the silver nanoparticles of about 6 nm in size increased with increasing the heat treatment time from 20 min to 180 min. The permittivity and tunability of the nano-Ag/PZT composite thin film were 120% and 46% higher than those of the PZT thin film without Ag nanoparticles, respectively.

The percolative BaTiO3-Ni0.5Zn0.5Fe2O4 (BTO-NZFO) ceramic composite represents a family of multifunctional materials exhibiting multiferroic properties and colossal apparent permittivity. It is of fundamental interest to investigate the conduction mechanism in such percolative composites from both macroscopic and microscopic perspectives. Herein, three representative systems with the NZFO content locating below the percolation threshold fc, near fc, and above fc, respectively, were investigated, using pure NZFO ceramic as a comparison. The conductivity of the composite as a function of NZFO content agrees well with the McLachlan model, which takes percolation into consideration and essentially equivalent to the Kirkpatrick model. The electrical conductivity of the composite conforms to Mott's variable-range-hopping (VRH) model in the temperature range of 303–573 K, suggesting that VRH conduction of localized polarons dominates the electrical behavior microscopically. Parameters including the most probable hopping range (R); the density of localized states at the Fermi level [N(EF)]; and the activation energies of VRH (W), dc conductivity (Edc), hopping (Eon), and relaxation (Er) were obtained and analyzed. Scaling behaviors of the conductivity and the imaginary part of complex impedance of the composite have been observed, implying that the distribution of relaxation times is temperature independent. The impedance data measured at different temperatures exhibit typical semiconducting behavior, which can be well fitted by an equivalent circuit model considering both grain and grain boundary responses. The correlation between conductivity and colossal apparent permittivity has also been revealed. The discoveries deepen the understanding of the conduction mechanism in such multifunctional composites composed of an insulating phase and a semiconducting phase.

Revealing the control of the formation and properties of multiferroic composite thin film is of great importance in fabricating multiferroic thin films with high performance and facilitating miniaturization and multi-functionalization of devices. In this work, BTO–NZFO nanocomposite thin films were synthesized on ITO-coated glass and quartz substrates by RF magnetron sputtering at sintering temperatures of 600–800 °C. The formation of composite thin films was investigated by means of XRD, SEM and XPS, and the thermodynamic calculation of activation energies of constituent phases was performed. The results show that, controlled by the stress from substrate and gradient activation energies, the crystallinities of the BTO and NZFO phases change continuously along the normal direction of the thin films, and increase with increasing distance from substrate. Below 30 nm, the composite thin films are mostly composed of amorphous phase without detectable grains, due to the too high activation energies of the constituent phases. Above 90 and 120 nm, respectively, the formation of BTO and NZFO crystalline phases in the composite thin films is free of any influence from the substrate and independent of the distance from the substrate, resulting from the small and stable activation energies. The measured permittivity and permeability values of the BTO–NZFO composite thin films, which are average values of all micro-layers with different crystallinities, are directly/strongly controlled by the continuously changeable activation energy along the normal direction of the thin film. Both values are high when the film is thick, and low when the film is thin.

M-type barium ferrite powders doped with Zr4+ ions (BaFe12−xZrxO19x = 0–0.4), possessing high permittivity and multi-resonant permeability, were synthesized by the sol–gel process. The single-phase hexagonal plate-like barium ferrites were formed with Zr4+ substituting Fe3+ at the 4f1 sites initially and then at the 2b sites afterwards with increasing doping content. The Ha of the ferrites decreased from 15.75 kOe to 8.13 kOe with increasing Zr4+ from x = 0 to 0.4. The e′ and e′′ of the ferrite with Zr4+ doping were increased to 7.7–6 and 3.4–1.5 over 18–40 GHz from 5.8–5 and 0.7–0.4 without doping, respectively. Contributed mainly by the enhanced permittivity, the matching thicknesses of the Zr4+ ions doped ferrites were as low as only ∼1 mm or below, i.e. 1.5–3 times thinner than those reported recently. The complex permittivity was still close to the complex permeability in the doped ferrites. Hence, a strong reflection loss of ∼−50 dB could be attained and the absorptivity of electromagnetic (EM) power per unit thickness reached as high as 0.156% μm−1, i.e. 2–5 times higher than those of novel absorbing materials. The multi-resonance permeability peaks originated from Fe3+ ions, and exchange couplings among Fe3+, Fe2+ and O− contributed multiple reflection loss peaks and thus, a broad bandwidth of ∼12 GHz (RL < −10 dB), which was 2–4 times broader than those normally reported. Consequently, the Zr4+-doped barium ferrites are promising for use as excellent absorbing materials in the millimeter wavelength frequency range.

Multiferroic composite is an environmentally friendly material with the extraordinary multisusceptible and high storage properties. It is significant to find an effective way for designing and fabricating high-quality materials. In this context, the BTO/NZFO nanocrystalline multiferroic composite thin films with and without (100) oriented spinel ferrite were prepared by RF magnetron sputtering. The saturation magnetization, coercivity, and initial susceptibility of composite thin films with (100) oriented spinel NZFO phase are 1.05, 1.75 to 2.08, and 1.15 times as high as those of the composites without orientation, respectively. The dc conductivity and dielectric loss of the composite thin film with (100) oriented NZFO are 18 and 33.3% lower than those of composite without orientation, respectively. It is exhibited that the magnetic and dielectric properties of the BTO/NZFO multiferroic composite thin films are azimuthally controlled by distribution of the Zn/Fe–O–Ni/Fe superexchange coupling and charge ...

WSe

The microstructure–property relation in ferroelectric/ferromagnetic composite is investigated in detail, exemplified by typical sol–gel-derived 0.3BTO/0.7NZFO ceramic composite. The effect of microstructural factors including intergrain connectivity, grain size and interfaces on the dielectric and magnetic properties of the composite prepared by conventional ceramic method and three-step sintering method is discussed both experimentally and theoretically. It reveals that the dielectric behavior of the composite is controlled by a hybrid dielectric process that combines the contribution of Debye-like dipoles and Maxwell–Wagner (M–W or interfacial) polarization. Enhanced dielectric, magnetic and conductive behaviors appear in the composite with better intergrain connectivity and larger grain size derived by sol–gel route and three-step sintering method. The effective permittivity contributed by Debye-like dipoles exhibits a value of ~130,000 in three-step sintered composite, which is almost the same as that in conventionally sintered one, but that contributed by M–W response is much smaller in the former. Compared with conventionally prepared samples, the relaxation time (τ) is 3.476 × 10−6 s, about one order of magnitude smaller, and the dc electrical conductivity is 3.890 × 10−3 S/m, one order of magnitude higher in three-step sintered composite. The minimum dielectric loss reveals almost the same (~0.2) for all samples, but shows distinguishable difference in low-frequency region. Meanwhile, an initial permeability of 84, twice as large as that of conventionally prepared composite and 56 % the value of single-phased NZFO ferrite (~150), and a saturation magnetization of 63.5 emu/g, 32 % higher than that of conventional one and approximately 84 % the value of single-phased NZFO ferrite (~76 emu/g), appear simultaneously in three-step sintered composite with larger grain size and better intergrain connectivity. It is clear that the discovery is helpful for establishing a more explicit view on the physics of multi-functional composite materials, while the composite with optimized microstructure is beneficial to be used as a high-performance material.

Revealing clearly the control of the microstructure on the dielectric and magnetic properties of multiferroic composites is of great importance in designing a composite with high performance. In this paper, BTO/NZFO composite thin films with solid solution constituent phases around 20 nm were prepared by RF magnetron sputtering. The lattice constant, grain size, intrinsic and extrinsic oxygen vacancies and non-stoichiometric defects in the nanocomposite thin film are measured by XRD, TEM and XPS. The conductivity, dielectric properties and magnetic performances of the nanocomposite are measured by an impedance analyzer and MPMS respectively. In this multisusceptible nanocomposite thin film, the permittivity is compatible with the Kirkpatrick model, and the dielectric loss is controlled importantly by the high fraction of grain boundaries which restrains the charge migration and thus makes the loss significantly low. The saturation magnetization of the nanocomposite thin film is influenced mainly by the lattice deformation of the nanosized constituent phases. The magnetic threshold of the nanocomposite shifts downwards from the real topological one, which is profitable for the composite to contribute simultaneously a low dielectric loss and high permeability. The coercivity, which is controlled by the grain size of NZFO and magnetic communication among NZFO nanoparticles, displays a novel percolation behavior.

BaTiO 3 /Ni 0.5 Zn 0.47 Fe 2 O 4 ceramic composites with various compositions were sintered at different temperatures. It is found both the formation and electromagnetic properties of the composite ceramics are strongly dependent on the percolation transition of NZFO. As NZFO content x is low ( x =0.1 and 0.2), the density increases with increasing the sintering temperature T from 1220 °C to 1300 °C, while it decreases as x is high ( x =0.65, 0.75 and 0.85). It is ascribed to the mismatch between the densification of BTO and NZFO. Both the permeability and low-frequency permittivity of the composites exhibit typical percolation behaviors, which are appropriate to the Kirkpatrick׳s effective medium model with the percolation threshold f c ranging from 0.35 to 0.5. As x f c , the permeability varies little and the low-frequency permittivity decreases with increasing T , owing to the dominant control of nonmagnetic BTO and the decrease in the defects in BTO, respectively. In comparison, as x > f c , both the permeability and permittivity increase considerably with increasing T . By analyzing the magnetic and dielectric dispersion spectra, it is revealed they are attributed respectively to the enhancement of domain-wall motion and the increase in the grain conductivity of NZFO.

PbZr0.52Ti0.48O3 thin films containing hexagonal and cubic Ag nanoparticles (Ag NPs) of various sizes were prepared using the sol–gel technique. During the aging process, Ag ions were photo-reduced to form hexagonal Ag NPs. These NPs were uniform in size, and their uniformity was maintained in the thin films during the heat treatment process. Both the total volume and average size of the hexagonal Ag NPs increased with an increasing Ag ion concentration from 0.02 to 0.08 mol l−1. Meanwhile, the remaining Ag ions were reduced to form unstable Ag–Pb alloy particles with Pb ions during the early heating stage. During subsequent heat treatment, these alloys decomposed to form cubic Ag NPs in the thin films. The absorption range of the thin films, quantified as the full width at half maximum in the ultraviolet–visible absorption spectrum, expanded from 6.3 × 1013 Hz (390–425 nm) to 8.4 × 1013 Hz (383–429 nm) as the Ag NPs/PZT ratio increased from 0.2 to 0.8. This work provides an effective way to broaden the absorption range and enhance the optical properties of such films.

A study on the magnetic properties of the BaTiO3(BTO)-NiZnFeO4(NZFO) nanocomposite thin films is presented to reveal the effect of percolation and resultant topological-microstructure-transition on the magnetic properties of the nanocomposites, which exhibit a critical behavior at the percolation threshold fc. An in-depth analysis was conducted from the perspectives of chemistry and physics both experimentally and theoretically by considering the microstructure and magnetic parameters of the nanocomposites. The results show that the anomalous behavior of the coercivity is jointly controlled by the exchange interaction between the ferrite nanoparticles and the grain size associated with the topological microstructure and composition of the nanocomposites. When the NZFO content is below the percolation threshold, the coercivity is mainly controlled by grain size, and the permeability is controlled by the equivalent demagnetizing field. When the NZFO content is above the percolation threshold, the coercivity is jointly affected by exchange interaction and grain size, while the suppression of the permeability by the equivalent demagnetizing field is greatly reduced. The findings may help establish a new paradigm of topological-microstructure-transition induced magnetic critical behaviors of percolative functional composites, and more and more evidences suggest that such effect may widely exist in various percolative systems.

Agx/PbZr0.52Ti0.48O3 (PZT, x defined as mole ratio of Ag/Pb) composite thin films were fabricated by the sol–gel technique. Results showed that the Agx/PZT thin films were composed of perovskite phase of PZT and silver nanoparticles. The silver nanoparticles with size between 4.5 and 7 nm were uniformly dispersed in the thin films. The percolation behavior occurred in the Ag/PZT thin films. The properties of PZT thin film were significantly improved as silver was introduced, especially as the fraction of silver nanoparticles was near the percolation threshold. The relative permittivity of the percolative Ag0.7/PZT thin film was 230 % higher than that of the single phased PZT thin film. The tunability of the percolative Ag0.7/PZT thin film was 57 % higher than that of the single phased PZT thin film. Meanwhile, the operating voltage for Ag0.7/PZT thin film supplying optimal tunability was only ~3 V (120 kV/cm), which was reduced by about 45 % compared to the single phased PZT thin film. The remanent polarization value of the Ag0.7/PZT percolative thin film was 22.9 μC/cm2, which was about 26 % higher than that of the single phased PZT thin film. While the coercive field of the Ag0.7/PZT percolative thin film was reduced by 29 %. It is attractive to be used as an electronic thin film with high performance.

The kaolinite–glycine intercalation compound was successfully formed by displacing intercalated guest water molecules in kaolinite hydrate as a precursor. The microstructure of the compound was characterized by X-ray diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscope. Results show that glycine can only be intercalated into hydrated kaolinite to form glycine–kaolinite by utilizing water molecules as a transition phase. The intercalated glycine molecules were squeezed partially into the ditrigonal holes in the silicate layer, resulting in the interlayer distance of kaolinite reaching 1.03 nm. The proper intercalation temperature range was between 20 °C and 80 °C. An intercalation time of 24 h or above was necessary to ensure the complete formation of kaolinite–glycine. The highest intercalation degree of about 84% appeared when the system was reacted at the temperature of 80 °C for 48 h. There were two activation energies for the intercalation of glycine into kaolinite, one being 21 kJ/mol within the temperature range of 20–65 °C and the other 5.8 kJ/mol between 65 °C and 80 °C. The intercalation degree ( N ) and intercalation velocity ( v ) of as a function of intercalation time ( t ) can be empirically expressed as N = −79.35 e − t /14.8 + 80.1 and v = 5.37 e − t /14.8 , respectively.

Multi-layered bottom electrodes constituted by conductive Ti5Si3 thin films with and without TiSi nanowires were prepared on glass substrates by Atmosphere Pressure Chemical Vapor Deposition (APCVD) method. Pb0.6Sr0.4(Ti0.97Mg0.03)O2.97 (PST) thin films were deposited on the Ti–Si bottom electrodes by Radio-frequency Magnetron Sputtering Method. The morphology and phase structure of the PST thin films were observed and identified by FE-SEM and XRD, respectively. The dielectric properties of the PST thin films deposited on Ti–Si substrates were measured by Agilent 4294A Impedance Analyzer. Results show that the formation ability of the PST thin films can be reinforced by increasing crystallinity of Ti5Si3 thin films and increasing amount of TiSi nanowires. The preparation temperature of the PST thin films deposited on Ti5Si3 and TiSi-nanowire/Ti5Si3 bottom electrodes decreases by 75 °C and 98 °C, respectively, compared with the situation on ITO/glass substrate. The permittivity of the PST thin films deposited on TiSi-nanowire/Ti5Si3 bottom electrode is about 4 times higher than that deposited on ITO. The lowest dielectric loss of PST/TiSi-nanowire/Ti5Si3 thin films is

(100) Oriented Pb x Sr1−x TiO3 (PSTO) thin films are prepared on indium tin oxide (ITO)/glass substrates by sol–gel technique while inserting doped PbTiO3 (PTO)-inducing layer in between. The effect of tensile stress in PSTO on tunability and (100) orientation of the thin films was investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscope, and atomic force microscope, respectively. Results show that PSTO thin film deposited on doped PTO has (100) oriented structure while it is randomly oriented when deposited directly on the ITO/glass substrate. Lattice mismatch between PSTO and PTO appears, in which the in-plane lattice constant c is 0.3922–0.3924 nm in the former and 4.02–4.07 nm in the latter, respectively, contributing tensile stress in the PSTO due to different lattice constants between them. The stress in the PSTO thin film is 3.04, 3.15, 3.59 and 4.47 GPa when the doped PTOs are Fe–PTO, Tb–PTO, Co–PTO and Zn–PTO, respectively. The orientation degrees of PSTO thin films are from 89.63, 90.31, 91.92 to 93.29 % with increasing stress of PSTO on Fe–PTO, Tb–PTO, Co–PTO and Zn–PTO, respectively. Tunabilities of the well-oriented PSTO thin films increase in ascending order of 63

Controlling the formation of conductive particles to be nano-scale is important for achieving percolation effect in metal dispersed thin film composite to contribute extraordinary dielectric properties required for miniaturization of electronic devices. In this paper, lactic acid (LA) and citric acid (CA) were used as dual complexing agents to prepare a typical Ag nanoparticle dispersed PbTiO 3 (PTO) composite thin film by using a sol-gel method. The phase structure of the thin film and the coordination effect between complexing agent and metallic ions were investigated. It revealed that LA coordinated with Ti 4 + and Pb 2 + and CA coordinated with Ag + . Lead was fixed inside the gel network by LA and restricted to evaporate during heat treatment thus the pyrochlore phase was prevented from forming in the thin film. Ag + was coordinated by CA and the diffusion and thus aggregation of silver during gelation and annealing process were weakened. Silver nanoparticles dispersed in the PTO matrix formed with dual complexing agents of LA and CA introduced during the preparation process. The composite thin film of perfect perovskite phase with silver nanoparticles embedded was obtained at the molar ratio of LA/lead = 0.5 and CA/lead = 0.5. The dielectric constant of the thin film with silver nanoparticles is 5 times higher than that without silver nanoparticles.

Ni@Ag core shell nanowires (NWs) were prepared by in situ chemical reduction of Ag+ around NiNWs as the inner core. Different Ni@Ag NWs with controllable morphologies were achieved through the layer-plus-island growth mode and this mechanism was confirmed by scanning electron microscopy, X-ray fluorescence, and X-ray photoelectron spectroscopy analyses. When used as a catalyst, the synthesized Ni@Ag NWs exhibited high reduction efficiency by showing a high reaction rate constant k of 0.408 s-1 in reducing 4-nitrophenol at room temperature. Besides, combining the magnetic property, including high saturation magnetization and low coercivity, the magnetic NiNW core contributes to excellent recyclability and long-term stability with only a 2.2% performance loss after 10 recycles by magnets. The Ni@Ag NWs proposed here show unprecedentedly high potential in applications requiring high efficiency and a recyclable catalyst.

The exploration of high-performance multiferroic composites is of great importance for the design of next-generation electromagnetic devices. In this article, BTO/NZFO, a universal percolative ceramic composite derived by sol–gel in situ method, was investigated both theoretically and experimentally. The composite exhibits super high percolation threshold (fc = 0.95) and thus giant permittivity as well as high permeability simultaneously. Glassy barrier layers at grain boundaries were designed to form in situ in the composite, leading to significant decrement in dielectric loss. Relaxation dispersion occurs in the composite with the relaxation time distributing from (6.0 to 2.0) × 10–7 s due to compositional discrepancy across the amorphous barrier layers at grain boundaries. The dielectric response of the composite can be described by hybrid dielectric model that combines both dipole polarization and space-charge polarization, theoretically supporting the view that amorphous barrier layers restraining th...

(100) Oriented (PbxSr1−x)TiO3 (PST) thin films were prepared on indium tin oxide coated glass substrates by sol–gel technique with rapid thermal processing. The dielectric permittivity and tunability of the thin films with different dispersion degrees of orientation were investigated in detail by characterizing the full width at half maximum of their (100) peak based on rocking curves at different annealing temperatures. Influence of orientation dispersion on dielectric properties was exhibited in the tunable dielectric thin films. It shows that the dielectric constant and hence the tunability of the sol–gel derived PST thin films are improved with the decrease in the dispersion degree of orientation of the perovskite phase other than the increase in the content of crystalline phase in the thin films. The dielectric constant (capacitance) and figure of merit of the oriented thin films are 3–6 times and 1 times higher than that of randomly oriented thin film respectively.

Pb 0.4 Sr 0.6 (Ti 0.97 Mg 0.03 )O 2.97 (PST) thin films were deposited on ITO/glass substrates with (1 0 0)/(0 0 1) oriented Tb-doped-PbTiO 3 (Tb-PT) layer inserted by magnetron sputtering method at room temperature. And the PST thin film is well-crystallized in (1 0 0) direction at annealing temperature of 600 °C for 30 min. The oriented Tb-PT layer promotes a (1 0 0) orientation, restrains structural distortion and improves phase quality of PST thin film. The (1 0 0) oriented PST thin film has higher permittivity and lower dielectric loss compared with the randomly oriented one. The tunability of the PST thin film is dramatically improved by 90% compared to that of randomly oriented PST without Tb-PT inserting layer, from 33% for randomly oriented PST without the inserting layer to 62.66% for the oriented one with the inserting layer. It is attractable to be used in high quality dielectric tunable devices.

The (1 0 0) oriented (Pb,Sr)TiO3 (PST) thin films were prepared using terbium-doped lead titanate as inducing layer. Misfit strain of the PST thin films changed gradually along direction of thickness and with different compositions. Controlled by the strain, the Curie temperature was independent of the composition of the PST and the width of the Curie peak was broadened. The as-prepared PST thin films exhibited stable high dielectric tunability which was almost independent of composition as well as applied temperature. With the composition of PST changing from PST35 (PbxSr1−xTiO3 x = 0.35) to PST50, the room temperature tunability of the PST thin films maintains a stable value of about 40%. At a high applied temperature of 200 °C, the PST thin films still show a high tunability of about 35%. The strain-assisted control of the Curie temperature and the Curie peak width is attractive in designing high stable devices with high dielectric tunability.

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H2O2) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM−1), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

Creating an environmentally friendly precursor to form a kaolinite intercalation compound is important for promoting the applications of nanohybrid kaolinite in electrochemical sensors, low- or zero-toxicity drug carriers, and clay-polymer nanocompounds. In the present study, a stable hydrated kaolinite precursor with d 001 = 0.84 nm was prepared successfully by heating the transition phase, the as-prepared kaolinite-hydrazine intercalate, at temperatures between 40 and 70°C. The structure of the hydrated kaolinite was characterized by X-ray diffraction and infrared spectroscopy. The morphology was examined using scanning electron microscopy. The results showed that the hydrated hydrazine of the transition phase was easy to decompose to hydrazines and water molecules in the interlayer at 40–70°C. Hydrazine molecules de-intercalated gradually, and water molecules remained in the ditrigonal holes of the silicate layer with sufficient stability, finally forming the stable 0.84 nm hydrated kaolinite in the system with a success rate of 80–90%. The 0.84 nm hydrated kaolinite may become an excellent precursor for the preparation of other kaolinite intercalates. A degree of intercalation of ~100% was obtained for the kaolinite-ethylene glycol intercalate, and a degree of intercalation of~80% was obtained for the kaolinite-glycine intercalate from the 0.84 nm hydrated kaolinite precursor.