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Abstract Next-generation advanced high/pulsed power capacitors rely heavily on dielectric ceramics with high energy storage performance. Although high entropy relaxor ferroelectric exhibited enormous potential in functional materials, the chemical short-range order, which is a common phenomenon in high entropy alloys to modulate performances, have been paid less attention here. We design a chemical short-range order strategy to modulate polarization response under external electric field and achieve substantial enhancements of energy storage properties, i.e. an ultrahigh energy density of ~16.4 J/cm3 with markedly improved efficiency ~90% at an electric field of 85 kV/mm in Nb doped (Bi0.2Na0.2K0.2La0.2Sr0.2) TiO3 system. Atomic-scale scanning transmission electron microscopy observations show that Nb exhibits a chemical short-range order structure, with Nb enriched regions displaying ultrasmall polar nanoregions and more flexible polarization configurations, which is conducive to achieving high maximum polarization and low residual polarization. Moreover, refined grain size of ~0.25μm, suppressed oxygen vacancies and enhanced bandwidth contribute to a high breakdown field strength. These collective factors result in exceptionally high energy storage density and efficiency. This short-range order strategy is expected to enhance the functional performances in other high entropy relaxor ferroelectrics.

Abstract Skyrmion bags, with arbitrary topological charge Q, have recently attracted much interest, since such high-Q topological systems could open a way for topological magnetism research and are promising for spintronic applications with high flexibility for information encoding. Investigation on room-temperature skyrmion bags in magnetic multilayered structures is essential for applications and remains unexplored so far. Here, we demonstrate room-temperature creation and manipulation of individual skyrmion bags in magnetic multilayered disks. Individual skyrmion bags with varying topological charges are identified to remain stable at zero field. Furthermore, we realize intriguing field-driven topological conversion of skyrmion bags, as well as local manipulation of skyrmion bags via magnetic tips. Micromagnetic simulations indicate that the special boundary condition of the disks is responsible for skyrmion-bag formation and stability. These findings provide a platform to investigate individual skyrmion bags in confined multilayered structures, which could be useful for developing high-Q-based topological spintronic devices.

The common approaches to control of skymions cause significant heat dissipation or require high electric fields near the breakdown threshold. Here, the authors demonstrate electric-field control of skyrmions through strain-mediated magnetoelectric coupling in multiferroic heterostructures.

Thermoelectrics can be capable of direct and reversible conversion between heat and electricity. Low dimensional thermoelectric materials, especially two dimensional (2D) thin films, have been considered as a breakthrough to decouple the correlations between electronic and thermal transport, contributing to the optimization of thermoelectric performance. During the past few decades, some effective strategies combined with physical concepts like quantum confinement effect, energy filtering effect, band structure tuning and interface engineering are introduced to design high performance thermoelectrics. Having a thorough understanding the underlying mechanisms is essential to develop thermoelectric materials. Here, our review summarizes the major strategies that can be utilized in thermoelectric thin films, including fabrication of superlattice structure, formation of two-dimensional electron gas (2DEG) system, orientation regulation, strain engineering and magnetic manipulation, from the aspects of deep mechanisms analyses, recent progress and prospects, inspiring significant improvement of thermoelectric properties.

Abstract Dental restorative materials with high mechanical properties and biocompatible performances are promising. In this work, polymer-infiltrated-ceramic-network materials (PICNs) were fabricated via infiltrating polymerizable monomers into porous ceramic networks and incorporated with hydroxyapatite nano-powders. Our results revealed that the flexural strength can be enhanced up to 157.32 MPa, and elastic modulus and Vickers hardness can be achieved up to 19.4 and 1.31 GPa, respectively, which are comparable with the commercial computer-aided design and computer-aided manufacturing (CAD/CAM) blocks. Additionally, the adhesion and spreading of rat bone marrow mesenchymal stem cells (rBMSCs) on the surface of such materials can be improved by adding hydroxyapatite, which results in good biocompatibility. Such PICNs are potential applicants for their application in the dental restoration.

Proton conducting SmNiO3 (SNO) thin films were grown on (001) LaAlO3 substrates for systematically investigating the proton transport properties. X-ray Diffraction and Atomic Force Microscopy studies reveal that the as-grown SNO thin films have good single crystallinity and smooth surface morphology. The electrical conductivity measurements in air indicate a peak at 473 K in the temperature dependence of the resistance of the SNO films, probably due to oxygen loss on heating. A Metal-Insulator-Transition occurs at 373 K for the films after annealing at 873 K in air. In a hydrogen atmosphere (3% H2/97% N2), an anomalous peak in the resistance is found at 685 K on the first heating cycle. Electrochemical Impedance Spectroscopy studies as a function of temperature indicate that the SNO films have a high ionic conductivity (0.030 S/cm at 773 K) in a hydrogen atmosphere. The activation energy for proton conductivity was determined to be 0.23 eV at 473–773 K and 0.37 eV at 773–973 K respectively. These findings demonstrate that SNO thin films have good proton conductivity and are good candidate electrolytes for low temperature proton-conducting Solid Oxide Fuel Cells. Keywords: SmNiO3, Thin film, Transport properties, Ionic conductivity, Impedance measurements

Although efforts have been put into the research in polymer-infiltrated ceramic network composites (PICNs), data are needed to understand the relationship between surface roughness and flexural strength. In this work, a novel dental restorative composite was fabricated via infiltrating mixtures of Bis-GMA/TEGDMA and UDMA/TEGDMA into partially sintered porous sodium aluminum silicate blocks and curing. Bars with different surface conditions were produced by sanding with abrasive and polishing. Flexural strength was measured using three-point-bending. Scanning electron microscopy (SEM) was employed to observe the microstructure of surface areas. One-way analysis of variance was applied for statistical calculations, with p < 0.05 being considered significant. Weibull plots were used to evaluate the reliability of flexural strength. The results demonstrated that the flexural strength of the resultant composites was affected by the scratch direction and the value of roughness. The flexural strength increased with decrease of surface roughness. A higher strength value was found for parallel types than for vertical types with nearly the same surface roughness. A large roughness value and a scratch direction perpendicular to tensile stress produced a low Weibull modulus. Of particular importance with this work is that these factors should be taken into consideration when using PICNs as dental restorative composites.

Polymer-based nanocomposites with excellent flexibility and intrinsic high breakdown strength are promising candidates for high energy density capacitors compared to ceramics counterparts. However, their energy density is relatively low due to the trade-off between permittivity and breakdown strength. In this work, the authors proposed a ferroconcrete-like structure for all-organic nanocomposites via combinatorial electrospinning and hot-pressing method. In this structure, polymethyl methacrylate (PMMA) serves as matrix while poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) serves as reinforcement phase. This novel structure is highly effective in breaking the paradox of improved discharged energy density with decreased efficiency, as evidenced by the concurrently improved discharged energy density (∼12.15 J/cm^3 compared to 8.82 J/cm^3 of the matrix) and efficiency (∼81.7% compared to 76.8% of the matrix). Compared to conventional blending composite films, samples with ferroconcrete-like structure exhibit higher permittivity, breakdown strength, discharged energy density and efficiency. The superior energy storage performance is attributed to large aspect ratio P(VDF-HFP) fibres distributed perpendicularly to the external field, which brings about the extra enhancement of permittivity. Besides, mechanical properties are improved and restriction on carrier motion is facilitated, leading to enhanced breakdown strength and suppressed conduction. This work provides a new way to design dielectric composite for high energy density and efficiency applications.

It has been suggested that the magnetic properties of metal layers using reversible redox reactions could form the basis of memory devices but this requires fast electric control to be practical. Here the authors demonstrate this on sub-millisecond timescales in a metal–oxide heterostructure.

Artificially fabricated 3d/5d superlattices (SLs) involve both strong electron correlation and spin-orbit coupling in one material by means of interfacial 3d-5d coupling, whose mechanism remains mostly unexplored. In this work we investigated the mechanism of interfacial coupling in LaMnO_{3}/SrIrO_{3} SLs by several spectroscopic approaches. Hard x-ray absorption, magnetic circular dichroism and photoemission spectra evidence the systematic modulation of the Ir ferromagnetism and the electronic structure with the change of the SL repetition period. First-principles calculations further reveal the mechanism of the SL-period dependence of the interfacial electronic structure and the local properties of the Ir moments, confirming that the formation of Ir-Mn molecular orbital is responsible for the interfacial coupling effects. The SL-period dependence of the ratio between orbital and spin components of the Ir magnetic moments can be attributed to the realignment of electron spin during the formation of the interfacial molecular orbital. Our results clarify the nature of interfacial coupling in this prototypical 3d/5d SL system and the conclusion will shed light on the study of other strongly correlated and spin-orbit coupled oxide heterointerfaces.

Epitaxial strain provides important pathways to control the magnetic and electronic states in transition-metal oxides. However, the large strain is usually accompanied by a strong reduction of the oxygen-vacancy formation energy, which hinders the direct manipulation of their intrinsic properties. Here, using a postdeposition ozone annealing method, we obtain a series of oxygen stoichiometric SrCoO_{3} thin films with the tensile strain up to 3.0%. We observe a robust ferromagnetic ground state in all strained thin films, while interestingly the tensile strain triggers a distinct metal-to-insulator transition along with the increase of the tensile strain. The persistent ferromagnetic state across the electrical transition therefore suggests that the magnetic state is directly correlated with the localized electrons, rather than the itinerant ones, which then calls for further investigation of the intrinsic mechanism of this magnetic compound beyond the double-exchange mechanism.

In the original version of this Article, Figs. 4c and 4d contained incorrectly sized error bars. This has now been corrected in both the PDF and HTML versions of the Article

Polycrystalline Bi2Se3−xTex (x = 0~1.5) samples were prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) and their thermoelectric properties were investigated. The SHS-SPS process can shorten the time with few energy consumptions, and obtain almost pure Bi2Se3-based phases. Consequently, the Se vacancies and anti-site defects contribute to the converged carrier concentration of ~2 × 1019 cm−3 while the increased carrier effective mass enhances the Seebeck coefficient to more than −158 μV K−1 over the entire temperature range. The lattice thermal conductivity is suppressed from 1.07 Wm−1 K−1 for the pristine specimen to ~0.6 Wm−1 K−1 for Te-substitution samples at 300 K because of point defects caused by the difference of mass and size between Te and Se atoms. Coupled with the enhanced power factor and reduced lattice thermal conductivity, a high ZT of 0.67 can be obtained at 473 K for the Bi2Se1.5Te1.5 sample. Our results reveal that Te-substitution based on the SHS-SPS method is highly-efficient and can improve the thermoelectric properties of Bi2Se3-based materials largely.

Pure BiFeO3 and heterostructured BiFeO3/BiFe0.95Mn0.05O3 (5% Mn-doped BiFeO3) thin films have been prepared by a chemical deposition method. The band structures and photosensitive properties of these films have been investigated elaborately. Pure BiFeO3 films showed stable and strong response to photo illumination (open circuit potential kept −0.18 V, short circuit photocurrent density was −0.023 mA·cm−2). By Mn doping, the energy band positions shifted, resulting in a smaller band gap of BiFe0.95Mn0.05O3 layer and an internal field being built in the BiFeO3/BiFe0.95Mn0.05O3 interface. BiFeO3/BiFe0.95Mn0.05O3 and BiFe0.95Mn0.05O3 thin films demonstrated poor photo activity compared with pure BiFeO3 films, which can be explained by the fact that Mn doping brought in a large amount of defects in the BiFe0.95Mn0.05O3 layers, causing higher carrier combination and correspondingly suppressing the photo response, and this negative influence was more considerable than the positive effects provided by the band modulation.

Cu3SbSe3-based composites have been prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) technology. Phase composition and microstructure analysis indicate that the obtained samples are mainly composed of Cu3SbSe3 phase and CuSbSe2/Cu2−xSe secondary phases. Our results show that the existence of Cu2−xSe phase can clearly enhance the electrical conductivity of the composites (~16 S/cm), which is 2.5 times higher than the pure phase. The thermal conductivity can remain at about 0.30 W·m−1·K−1 at 653 K. A maximum ZT (defined as ZT = S2σΤ/κ, where S, σ, Τ, κ are the Seebeck coefficient, electrical conductivity, absolute temperature and total thermal conductivity) of the sample SPS 633 can be 0.42 at 653 K, which is 60% higher than the previously reported values. Our results indicate that the composite structure is an effective method to enhance the performance of Cu3SbSe3.

BiCuSeO has recently been shown to be one of the best oxide-based thermoelectric materials. The electrical properties of this material have been widely studied; however, the reasons for its intrinsically low thermal conductivity have only been briefly discussed. In this paper, we calculated the band structure and the electrical properties of BiCuSeO. The phonon spectrum, mode Grüneisen parameters and the thermal properties were also investigated. Additionally, we proposed a new method for illustrating the interlayer interactions in this material. For the first time, using first principles calculations, we provide direct evidence of the structural in-layer and interlayer off-phase vibration modes, which contribute to the anharmonic vibrations and structural scattering of phonons and result in an intrinsic low lattice thermal conductivity for BiCuSeO.

A general procedure and characterization of a family of single-crystal chromate nanorods/nanobelts by hydrothermal treatment is presented. It shows that pH 7 is the optimal condition for the formation of chromate 1D nanostructures and the pH in the reaction solution will be lowered when surfactants added into it.

Magnetoelectric bilayered Pb(Zr0.52Ti0.48)O3-CoFe2O4(PZT-CFO) films with different PZT thicknesses were grown on (111)Pt/Ti/SiO2/Si substrates using chemical solution spin-coating. Structural characterization by X-ray diffraction and electron microscopy shows pure phases and well-defined interfaces between the PZT and CFO films. The CFO-PZT-substrate structure effectively alleviates the substrate clamping effect for the CFO layer, showing appreciable magnetoelectric responses in the composite films. Both the direct magnetoelectric effect and the magnetic field-induced Raman shifts in the A1(TO1) soft mode of PZT demonstrate the magnetic- mechanical-electric coupling in the films. The results also indicate that with a constant CFO layer thickness, the thickness of the PZT layer plays an important role in the stress relaxation and strong magnetoelectric coupling. The coupling could be further enhanced by increasing the CFO thickness, optimizing the volume (thickness) fraction of the PZT thickness, and releasing the clamping effect from the substrate. [ABSTRACT FROM AUTHOR]

Two-dimensional transition-metal dichalcogenides semiconductors (TMDCs) with layered structures have been concerned as promising thermoelectric (TE) materials for several years. However, WSe2 as one of TMDCs is barely investigated. Herein, we systematically investigated the high-temperature electrical and thermal transport behaviors in layered structure WSe2, demonstrating that WSe2 possesses high Seebeck coefficient and low thermal conductivity. The study of sintering process shows that the best electrical properties can be obtained in the sample sintered at 1123 K. Besides, anisotropic thermoelectric properties were also revealed. It is found that the dimensionless figure of merit (ZT) in the direction parallel to the pressing direction is higher than that in the direction perpendicular to the pressing direction. The highest ZT value of 0.03 is obtained at 923 K, which is an appreciable value for the pristine alloy material. [ABSTRACT FROM AUTHOR]

Polycrystalline Bi2Se3-xTex (x = 0~1.5) samples were prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) and their thermoelectric properties were investigated. The SHS-SPS process can shorten the time with few energy consumptions, and obtain almost pure Bi2Se3-based phases. Consequently, the Se vacancies and anti-site defects contribute to the converged carrier concentration of ~2 × 1019 cm-3 while the increased carrier effective mass enhances the Seebeck coefficient to more than -158 µV K-1 over the entire temperature range. The lattice thermal conductivity is suppressed from 1.07 Wm-1 K-1 for the pristine specimen to ~0.6 Wm-1 K-1 for Te-substitution samples at 300 K because of point defects caused by the difference of mass and size between Te and Se atoms. Coupled with the enhanced power factor and reduced lattice thermal conductivity, a high ZT of 0.67 can be obtained at 473 K for the Bi2Se1.5Te1.5 sample. Our results reveal that Te-substitution based on the SHS-SPS method is highly-efficient and can improve the thermoelectric properties of Bi2Se3-based materials largely. [ABSTRACT FROM AUTHOR]

Well-dispersed Co/CoO/C nanospheres have been designed and constructed through a facile electrospinning method with a strategy controlling the morphology of nanocomposites via adjusting the pre-oxidized and heat treatments. Scanning electron microscopy results reveal that the as-synthesized sample pre-oxidized at 275 °C shows better spherical morphology with a diameter of around 300 nm without conspicuous agglomeration. X-ray diffraction analysis confirms the coexistence of cobalt and cobalt monoxide in the sample. Furthermore, the electrochemical tests reveal that the sample pre-oxidized at 275 °C displays excellent cycling stability with only 0.016% loss per cycle even after 400 cycles at 1000 mA·g-1 and enhanced high-rate capability with a specific discharge capacity of 354 mA·g-1 at 2000 mA·g-1. Besides, the sample pre-oxidized at 275 °C shows a specific capacity of 755 mA·g-1 at 100 mA·g-1 after 95 cycles. The improved electrochemical performance has been ascribed to the well dispersion of nanospheres, the improved electronic conductivity, and the structural integrity contribution from the carbon and cobalt coexisting nanocomposite. The strategy for preparing well-dispersed nanospheres by adjusting pre-oxidized and annealing processes could have insight for other oxide nanosphere synthesis. [ABSTRACT FROM AUTHOR]

Pure BiFeO3 and heterostructured BiFeO3/BiFe0.95Mn0.05O3 (5% Mn-doped BiFeO3) thin films have been prepared by a chemical deposition method. The band structures and photosensitive properties of these films have been investigated elaborately. Pure BiFeO3 films showed stable and strong response to photo illumination (open circuit potential kept ~0.18 V, short circuit photocurrent density was ~0.023 mA.cm-2). By Mn doping, the energy band positions shifted, resulting in a smaller band gap of BiFeO3/BiFe0.95Mn0.05O3 layer and an internal field being built in the BiFeO3/BiFe0.95Mn0.05O3 interface. BiFeO3/BiFe0.95Mn0.05O3 and BiFeO3/BiFe0.95Mn0.05O3 thin films demonstrated poor photo activity compared with pure BiFeO3 films, which can be explained by the fact that Mn doping brought in a large amount of defects in the BiFeO3/BiFe0.95Mn0.05O3 layers, causing higher carrier combination and correspondingly suppressing the photo response, and this negative influence was more considerable than the positive effects provided by the band modulation. [ABSTRACT FROM AUTHOR]

Cu3SbSe3-based composites have been prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) technology. Phase composition and microstructure analysis indicate that the obtained samples are mainly composed of Cu3SbSe3 phase and CuSbSe2/Cu2–xSe secondary phases. Our results show that the existence of Cu2–xSe phase can clearly enhance the electrical conductivity of the composites (~16 S/cm), which is 2.5 times higher than the pure phase. The thermal conductivity can remain at about 0.30 W.m-1.K-1 at 653 K. A maximum ZT (defined as ZT = S2σT/κ, where S, σ, T, κ are the Seebeck coefficient, electrical conductivity, absolute temperature and total thermal conductivity) of the sample SPS 633 can be 0.42 at 653 K, which is 60% higher than the previously reported values. Our results indicate that the composite structure is an effective method to enhance the performance of Cu3SbSe3. [ABSTRACT FROM AUTHOR]

Composite ceramics BaTiO3/3Y-TZP containing 0 mol %, 3 mol %, 5 mol %, 7 mol %, and 10 mol % BaTiO3 have been prepared by conventional sintering and spark-plasma sintering (SPS), respectively. Analysis of the XRD patterns and Raman spectra reveal that the phase composition of t-ZrO2, m-ZrO2, and BaTiO3 has been obtained. Our results indicate that SPS can be effective for the decrease in grain size and porosity compared with conventional sintering, which results in a lower concentration of m-ZrO2 and residual stress. Therefore, the fracture toughness is enhanced by the BaTiO3 phase through the SPS technique, while the behavior was impaired by the piezoelectric second phase through conventional sintering. [ABSTRACT FROM AUTHOR]

Zirconia ceramics with porous structure have been prepared by solid-state reaction using yttria-stabilized zirconia and stearic acid powders. Analysis of its microstructure and phase composition revealed that a pure zirconia phase can be obtained. Our results indicated that its porosity and pore size as well as the mechanical characteristics can be tuned by changing the content of stearic acid powder. The optimal porosity and pore size of zirconia ceramic samples can be effective for the increase of surface roughness, which results in higher cell proliferation values without destroying the mechanical properties. [ABSTRACT FROM AUTHOR]

Bi1-xLaxCuSeO ceramic bulks have been prepared by the spark plasma sintering method. Our results indicate that La-doping can lead to an obvious change of the band structure evidenced by the absorption spectra and electric transportation behaviors (e.g., m* and Seebeck coefficient). The variation of band structure results in a great enhancement of carrier mobility caused by a decreased energy offset between the primary and secondary valence bands. A maximum ZT value of 0.74 can be obtained in 8% La-doped BiCuSeO sample at 923 K, which is 37% higher than that of the pure BiCuSeO bulk. Our results reveal that band engineering is an effective way to enhance the thermoelectric properties of BiCuSeO system. [ABSTRACT FROM AUTHOR]

We report that thin films of a prototype topological insulator, Bi2Se3, can be epitaxially grown onto the (0001) surface of BaFe12O19 (BaM), a magnetic insulator with high Curie temperature and large perpendicular anisotropy. In the Bi2Se3 thin films grown on non-magnetic substrates, classic weak antilocalization (WAL) is manifested as cusp-shaped positive magnetoresistance (MR) in perpendicular magnetic fields and parabola-shaped positive MR in parallel fields, whereas in Bi2Se3/BaM heterostructures the low field MR is parabola-shaped, which is positive in perpendicu- lar fields and negative in parallel fields. The magnetic field and temperature dependence of the MR is explained as a consequence of the suppression of WAL due to strong magnetic interactions at the Bi2Se3/BaM interface. [ABSTRACT FROM AUTHOR]

The article cities a research study that examines the crystal structures and the valence states of a novel self-assembled MnO double layer by using atomically resolved scanning transmission electron microscopy and spectroscopy, and functional theory (DFT) calculations. The occurrence of multiple couplings between charge and lattice in this novel double layer was detected.

Two-dimensional transition-metal dichalcogenides semiconductors (TMDCs) with layered structures have been concerned as promising thermoelectric (TE) materials for several years. However, WSe2 as one of TMDCs is barely investigated. Herein, we systematically investigated the high-temperature electrical and thermal transport behaviors in layered structure WSe2, demonstrating that WSe2 possesses high Seebeck coefficient and low thermal conductivity. The study of sintering process shows that the best electrical properties can be obtained in the sample sintered at 1123 K. Besides, anisotropic thermoelectric properties were also revealed. It is found that the dimensionless figure of merit (ZT) in the direction parallel to the pressing direction is higher than that in the direction perpendicular to the pressing direction. The highest ZT value of 0.03 is obtained at 923 K, which is an appreciable value for the pristine alloy material. [ABSTRACT FROM AUTHOR]