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High-performance environment-friendly piezoelectric potassium sodium niobate (KNN)-based thin films have been emerged as promising lead-free candidates, while their substrate-dependent piezoelectricity faces the lack of high-quality information due to restraints in measurements. Although piezoresponse force microscopy (PFM) is a potential measuring tool, still its regular mode is not considered as a reliable characterization method for quantification. After combining machine-learning enabled analysis using PFM datasets, it is possible to measure piezoelectric properties quantitatively. Here we utilized advanced PFM technology empowered by machine learning to measure and compare the piezoelectricity of KNN based thin films on different substrates. The results provide a better understanding of the relationship between structures and piezoelectric properties of the thin films.

Photogenerated electrons (e−) and holes (h+) easily undergo fast recombination in many semiconductors, limiting the further improvement of its photocatalytic efficiency. To solve this bottleneck problem, graphitic C3N4 was used to group tetragonal-phase BaTiO3 ferroelectric and successfully constructed the g-C3N4/BaTiO3 heterojunction via a facial mixing-calcination method. These composites exhibited an extraordinary improvement under visible-light irradiation, achieving a “1 + 1>2” performance compared with their single pristine components. It is because the formation of double-transfer structure promotes the fast transfer of photo-induced charge carriers in g-C3N4/BaTiO3 composites. Synergy between the two materials, especially the ferroelectric polarization, plays a key role in facilitating the spatial separation of photo-excited e−/h+ pairs and improving the photocatalytic efficiency.

Beside the extraordinary structural, mechanical and physical properties of two-dimensional (2D) materials, the capability to tune properties via strain engineering has shown great potential for nano-electromechanical systems. External strain, in a controlled manner, can manipulate the optical and electronic properties of the 2D materials. We observed the lattice vibration modulation in strained mono- and few-layer tantalum sulfide (TaS2). Two Raman modes, E1g and E12g, exhibit sensitive strain dependence, with the frequency of the former intensity increasing and the latter decreasing under a compressive strain. The opposite direction of the intensity shifts, which cannot be explained solely by van der Waals interlayer coupling, is attributed to strain-induced competition between the electron–phonon interlayer coupling and possible stacking-induced changes of the intralayer transport. Our results enrich the understanding of the lattice vibration of TaS2 and point to strain engineering as a powerful tool for tuning the electron–phonon coupling of 2D materials.

Friction-driven contaminant degradation is a novel and potential solution to mitigate environmental pollution. However, the core mechanism of tribocatalytic degradation remains elusive. To understand the key parameters that affect tribocatalytic performance, we have synthesized CdS semiconductor nanowires with controllable piezoelectric properties. Intriguingly, only under magnetic stirring can these CdS nanowires degrade rhodamine B organic dye (as a representative organic pollutant) highly effectively in the dark, overcoming the drawback of the intermittent nature of sunlight in photocatalysis. In addition, the efficiency of tribocatalysis can be greatly improved through enhancing the friction or increasing the interfacial area between the stirring rods and the container. Further analysis indicates that piezoelectric CdS nanowires with higher aspect ratios enable more efficient charge carrier separation and transfer, playing a pivotal role in enhancing the degradation of organic compounds. Our findings blaze a new trail for removing harmful pollutants from wastewater and pave the way for many important applications through utilizing friction energy.

Magnetoelectric materials have been considered as promising candidates for data storage and sensors based on spintronic technology. Multiferroic BiFeO3–CoFe2O4 (BFO–CFO) epitaxial thin films deposited on a (111)-oriented SrTiO3 substrate exhibit ferromagnetism, piezoelectricity and strong magnetoelectric properties simultaneously. Interfacial strain between two phases plays a key role in such unique characters. Thus, strain engineering is a good method to enhance the magnetoelectric coupling effect. Here, to clearly understand the role of strain for further strain engineering, the interfacial strain between BFO and CFO and its evolution under electric/magnetic fields are investigated. This work semiquantitatively establishes a detailed relationship between the magnetoelectric coupling effect and interfacial strains – the piezoelectric amplitude drops by 44.7% and meanwhile the out-of-plane tensile strain rises by 11.0% under magnetic fields. This finding is helpful in optimizing multiferroic composite structures and achieving wider applications in future.

Corrosion-induced nitrogen (N) leaching limits the long-term applications of N-doped carbon (NC) catalysts for electrocatalytic oxygen reduction reaction (ORR). Anchored N for NC can suppress their corrosion and thus restrain the loss of catalytically active sites, resulting in the improved ORR durability. Herein, we report our strategies to suppress the leaching of N by embedding the NiCo alloy nanoparticles in NC nanowires and thus creating the interfacial metal-N units (M-N) for the robust ORR durability in alkali over 50 h. Also, the synergistic effects of Ni/Co–N, abundant active sites and favourable kinetics bring the high ORR activity over the Pt/C benchmark. Thus, our strategies with the improved durability and activity could create promising ORR catalysts with ∼5 times of activity-durability factor over the NC catalysts.

Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals exhibit ultrahigh piezoelectric property and have already been applied in various industrial fields. Here, spatial distribution of coexistent phases and corresponding local piezoelectric responses in a morphotropic phase boundary (MPB) PMN-xPT single crystal are thoroughly investigated by confocal Raman spectroscopy coupled with piezo-response force microscopy (PFM). Different from previous studies on MPB crystals, spatial distribution of coexistent phases is exhibited intuitively in an image obtained by confocal Raman mapping. Via in-situ PFM measurements, domain morphology of each coexistent phase is observed. Moreover, local piezoelectric responses of each coexistent phase are obtained by switching spectroscopy PFM measurements, indicating that Ma and Mc phases behave like PNRs and polar matrix in PMN-xPT crystals Our work clarifies the contribution from different phases to the giant piezoelectric performance, which can deepen the understanding on the ultrahigh piezoelectricity in PMN-xPT crystals and provide the key point for developing novel high piezoelectricity materials.

The electrocaloric effect in ferroelectric materials has drawn much attention due to its potential applications in integrated circuit cooling and novel cooling devices. In contrast to the widely researched positive electrocaloric effect, the negative electrocaloric effect has received much less attention due to the lack of any effective methods for significant enhancement. In this work, we fabricated PbZrO3 thin film on a Pt/Si substrate by the sol-gel method. By controlling the interface conditions between the thin film and substrate, we induced defects into the interface and stabilized a transient ferroelectric phase in the PbZrO3 thin film. The emergence of the transient ferroelectric phase postpones the antiferroelectric-ferroelectric phase transition. As a result, a negative electrocaloric effect up to -18.5 K is estimated near room temperature, the highest one ever reported in this temperature range. This result suggests a new strategy to enhance the negative electrocaloric effect and may benefit the application of PbZrO3 thin films in cooling devices.

Core-shell nanoparticles used as blocks to construct composite ceramics can exhibit high energy storage density, but the effects of original tunable shell thickness on the microstructures and energy storage property of finally sintered bulk ceramics has not been clarified, thus how to achieve the full potential of this technology to improve the energy storage density of ferroelectric-based ceramics remains to be solved. In this study, as precursors to fabricate bulk ceramics, BaTiO3@SiO2 core-shell nanoparticles were successfully synthesized by a wet-chemical method and they were used as models to investigate the effect of the core-shell nanostructured precursors on the energy storage property of the bulk composite ceramics. The original BaTiO3 nanoparticles coated with various homogenous SiO2 shells were acquired by controlling the concentration of tetraethyl orthosilicate (TEOS). The surface microstructure of the bulk composite ceramics observed by scanning electron microscope (SEM) revealed that the SiO2 outer shell of BaTiO3@SiO2 nanoparticles plays an important role in constructing the microstructure of the ceramics. The remodeled microstructure has a great impact on leakage current density and dielectric property, and it makes a leading contribution to the energy storage performance of ceramics. As a result, the optimum SiO2 loading range was confirmed and the maximum energy storage density obtained from BaTiO3@20 wt%SiO2 was ∼4.799 J/cm3 at 370 kV/cm, demonstrating that nanoscale core-shell architecture is an effective strategy to improve the energy storage performance of ferroelectric-based composite ceramics.

NaNbO3 with oxygen vacancies has been successfully synthesized through a well controllable solid-state reaction, whose photocatalytic performances have been prominently enhanced by almost 2.4 times compared with just annealed NaNbO3 (the control sample). When oxygen vacancies were introduced into the perovskite, the color of NaNbO3 turned black and the band gap was decreased, resulting in its remarkable absorption under visible light, and its higher symmetry also favors the electron transfer. More importantly, oxygen vacancies lead to larger specific surface area and higher charge density, which play non-negligible roles in improving the visible-light-activities. These encouraging findings prove that oxygen vacancy engineering is a feasible and general strategy to improve the photocatalytic performances of perovskite oxides, which will promote many related applications.

Beside the extraordinary structural, mechanical and physical properties of two-dimensional (2D) materials, the capability to tune properties

While creating open nanostructures represents a popular strategy for improving the utilization efficiency of Pt-based catalysts for electrochemical reactions, the exposed facets should be precisely controlled for further enhancement of the catalytic activity. Here, we report a novel strategy for creating regularly shaped nanopores in ultrathin nanotubes of bimetallic noble metals. By templating against Ag nanowires and then applying a thermal ripening process, we have successfully produced ultrathin (with a wall thickness of ∼1 nm) Pt–Ag alloy nanotubes containing high-density well-defined rectangular nanopores and a collapsed double-layer structure. The resulting porous nanotubes expose {100} facets at the basal sides and {110} facets with step sites at the edges of the rectangular nanopores. The particular surface structure and the bimetallic composition enable suppressed CO poisoning of the catalysts and consequently enhanced electrocatalytic activity in the methanol oxidation reaction. The typical spe...

Mechanisms of the dielectric relaxation and electric field induced dipole re-orientation process in the 0.6BaTiO 3 -0.4Bi(Mg 1/2 Ti 1/2 )O 3 ceramic have been investigated by a combination of experiments and simulations. Using the modified Debye relaxation theory, the observed strong relaxation is related to the evolution of the distribution of relaxation times with increasing temperatures. The increased freezing temperature under dc bias electric fields indicates that the nonlinear dielectric behavior has positive contributions to the total polarization. In relaxor state, the dielectric response of the 0.6BaTiO 3 -0.4Bi(Mg 1/2 Ti 1/2 )O 3 ceramic shows a maximum value with the increasing external fields, which is attributed to two main polarization mechanisms, lattice phonon polarization and re-orientation of polar clusters. The contribution of these two polarization mechanisms is separated by the multi-polarization model, indicating that the re-orientation of polar clusters is responsible for the increase of the dielectric constant. At last, Monte Carlo method is performed to simulate the dipole re-orientation process, and the simulated results are consistent with experimental findings. This study provides a different perspective to investigate the relaxor materials with isolated polar clusters.

Conventional computing based on von Neumann architecture cannot satisfy the demands of artificial intelligence (AI) applications anymore. Neuromorphic computing, emulating structures and principles based on the human brain, provides an alternative and promising approach for efficient and low consumption information processing. Herein, recent progress in neuromorphic computing enabled by emerging two-dimensional (2D) materials is introduced from devices design and hardware implementation to system integration. Especially, the advances of hopeful artificial synapses and neurons utilizing the resistive-switching-based devices, 2D ferroelectric-based memories and transistors, ultrafast flash, and promising transistors with attractive structures are highlighted. The device features, performance merits, bottlenecks, and possible improvement strategies, along with large-scale brain-inspired network fulfillment, are presented. Challenges and prospects of system application for neuromorphic computing are briefly discussed, shedding light on its great potential for AI.

Ferroelectric materials have multiple characteristics in ferroelectric, piezoelectric, pyroelectric properties, which provide an attractive prospect for simultaneously harvesting multiple energy sources for catalytic applications. However, the crucial challenge for wastewater purification lies in the development of ferroelectric materials with improved functions and the design of advanced oxidation processes. Herein, Sr0.3Ba0.7TiO3 (SBT-0.3) nano-catalysts modified by PVP surfactant could significantly promote water recovery efficiency from the rhodamine B (RhB), which is as high as 98% by simultaneously collecting two types of energy sources of mechanical friction and temperature fluctuation from the natural environment for tribo-/pyro-catalysis under dark conditions. It was found that the samples containing PVP surfactant show significantly improved performance in the separation of charge carriers in comparison with those without PVP surfactant. The permanent polarization in SBT-0.3, coupled with the piezo-/pyro-potential, could generate internal field and therefore reduce charge recombination. It also helps to absorb charged species from the dye solution, which favors the reaction with active oxygen to cause the cleavage and breakdown of organic molecules. The mechanism of RhB decomposition mediated by SBT-0.3 ferroelectric is also discussed. This work favors us to in-depth understanding for the tribo-/pyro-catalysis and hence proposes a new strategy to improve the water purification efficiency of ferroelectric nanocrystals.

In this work, the (100-x)Ba(Hf 0.2 Ti 0.8 )O 3 -x(Ba 0.7 Ca 0.3 )TiO 3 (BHT–xBCT) ferroelectric ceramics were fabricated by a conventional solid-state reaction method. The electrocaloric effect (ECE) of these ceramics was studied by both indirect and direct methods over a wide temperature range with the composition changing from x = 20 to 50. The most excellent direct ECE occurs in the BHT–50BCT with a good direct ΔT EC = 0.27 K (at 92 °C) under the electric field of 10 kV/cm. What's more, the direct EC effect peaks not only locates at near the Curie temperature, but also at the phase-transition temperatures corresponding to the transitions between different ferroelectric phases. In particular, it is found that BHT–50BCT exhibits a direct ECE anomaly ΔT EC = 0.1 K at 30 °C under an electric field of 10 kV/cm, which can be ascribed to the orthorhombic to tetragonal phase transition, proposing that one can achieve a broad temperature window by tuning the temperature gap between ferroelectric (FE) to paraelectric (PE) boundary and FE-FE boundary. In addition, BHT–30BCT shows good stability of indirect ΔT EC,max /ΔE and a broad ECE peak at a higher electric field, indicating that it is possible for electrocaloric temperature ΔT EC to be tuned linearly by electric field. Overall, our results imply that the BHT– xBCT ceramics are promising candidates for lead-free cooling refrigeration applications.

Moisture has been reported to be positive for organic-inorganic halide perovskite films formation during their annealing process in several literatures. Here we report a comprehensive study of moisture effect on the annealing process of CH 3 NH 3 PbI 3 films deposited by solvent engineering method. Perovskite intermediate phase films are deposited by spin coating in a glove box and then annealed in the glove box or air with different humidity. Different from previous reports, the presence of moisture dramatically deteriorates the film morphology, and too high humidity even retards the formation of the perovskite from its intermediate phase. However, the crystallinity, conductivity and optical properties of the films are greatly improved, which in turn contributes to a much better device performance. This work suggests that the effect of moisture annealing on perovskite films is closely related to the deposition method and composition, and the deterioration of surface morphology does not necessarily lead to worse device performance.

Control of coupling between electric and elastic orders in ferroelectric bulks is vital to understand their nature and enrich the multifunctionality of polarization manipulation applied in domain-based electronic devices such as ferroelectric memories and data storage ones. Herein, taking (1 - x%)Pb(Mg1/3Nb2/3)O3-x%PbTiO3 (PMN-x%PT, x = 32, 40) as the prototype, we demonstrate the less-explored mechanical switching in relaxor ferroelectric single crystals using scanning probe microscopy. Low mechanical forces can induce metastable and electrically erasable polarization reversal clearly from electrical-created bipolar domains around the 180° domain wall in monoclinic PMN-32%PT and inside the c+ domain in tetragonal PMN-40%PT. The mechanical switching evolutions show force/time dependence and time-force equivalence. The time-dependent mechanical switching behavior stems from the participation and contribution of polar nanoregions. Flexoelectricity and bulk Vegard strain effect can account for the mechanical switching but notably, the former in the two has very different origins. These investigations exhibit the possibility of mechanical switching as a tool to manipulate polarization states in ferroelectric bulks, and provide the potential of these crystals as substrates in mechanical polarization control of future thin-film devices.

The electrocaloric effect in ferroelectric materials has drawn much attention due to its potential applications in integrated circuit cooling and novel cooling devices. In contrast to the widely researched positive electrocaloric effect, the negative electrocaloric effect has received much less attention due to the lack of any effective methods for significant enhancement. In this work, we fabricated PbZrO

Ferroelectrics’ structure-property relationships are of guiding significance in high-performance material designing and usually clarified from the aspect of symmetries, which is arduous and costly. On the principle of convenience, here, the concept that domains can provide a brandnew nondestructive and fast way for this relationship clarification is demonstrated. Utilizing scanning probe microscopy, quantitative original local elastic/piezoelectric/ferroelectric performances of various characteristic domain configurations are directly investigated in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals. Among them, the polygonal lamellar domains with coexistence of straight c, a and c/a walls in the at-morphotropic phase boundary composition, own high surface effective Young's modulus (average values close to 160 GPa), strong original average local piezoresponse (8.5 pm) and effective longitudinal piezoelectric response (d33, 14 pm V−1), together with ease of electrical switching. Low free energy barrier and strong piezoelectric anisotropy contribute intrinsically to these better functionalities. Higher and easier domain wall motion, larger ratio of c+/c− domains, and larger depolarization and elastic energies stemmed from larger domain width/size act as extrinsic factors. These results help to understand relaxor ferroelectrics comprehensively and provide a reference of domain-based structure selection for better material design.

Nanocomposites incorporating inorganic nanoparticles (NPs) within ferroelectric polymeric matrices have great potential for high density energy capacitors. In this strategy, employing the nanostructures with specially designed morphology as fillers would notably improve the energy storage. However, this strategy is extremely challenging and has not been largely explored. Here, the BaTiO3@sheet-likeTiO2 core–shell NPs have been successfully synthesized, and can be well-dispersed into polyvinylidene fluoride (PVDF) matrices. The nanocomposites with the volume fraction 2.5% BT@TiO2 NPs have higher the electric displacement (6.0 μm/cm2) than that of PVDF films with the 2.5 vol % BaTiO3 (BT) NPs (5.1 μm/cm2) under the same electric field of 350 kV/mm, which is mainly ascribed to the hierarchical interfacical polarization induced by the large surface area of TiO2 sheet assembled on BT NPs in the nanocomposites. Simultaneously, the medium permittivity TiO2 with medium er as a buffer layer between the BT NPs and ...

A giant electrocaloric effect (ECE) can be achieved in ferroelectric thin films, which demonstrates the applications of thin films in alternative cooling. However, electrocaloric thin films fabricated by conventional techniques, such as the pulsed laser deposition or sol–gel methods, may be limited by high costs, low yield and their dependence on substrates. In this study, we present a new bottom-up strategy to construct electrocaloric Ba0.8Sr0.2TiO3 thin films by assembling precisely designed building blocks of ferroelectric nanocubes, which is supported by detailed structural characterization. Moreover, it is found that our assembled Ba0.8Sr0.2TiO3 films differ remarkably from both individual Ba0.8Sr0.2TiO3 NPs and bulk Ba0.8Sr0.2TiO3 ceramics in terms of new collective ferroelectric properties, including superior and diffused permittivity constants and polarization-electric field loops. Benefiting from these unique ferroelectric properties, a giant ECE (9.1 K) over a broad temperature range (20 °C to 60 °C) is achieved, which is very large in the lead-free oxide film. Clearly, this bottom-up strategy provides a promising pathway for developing high electrocaloric effect devices.

Most ferroelectric transitions occur ultrafast and are time independent. However, here in (1-x) (Bi0.5Na0.5)TiO3-xBaTiO3, we have found a ferroelectric phase transition induced solely by increasing waiting time at certain temperatures (isothermal phase transition). Through cooling, a unique metastable state between a relaxor ferroelectric and a ferroelectric is unveiled, which in essence is initially a short-range ordered glassy state and then can evolve into a long-range ordered ferroelectric state through the isothermal process. It is also found that these isothermal ferroelectric transitions only occur within a specific temperature region with different waiting time needed. These features of isothermal phase transition can be understood by Landau theory analysis with the consideration of random defects as a competition between the thermodynamically favored long-range ordered state and the kinetically frustrated short-range ordered glassy state from random defects. This study offers a precise experimental as well as a phenomenological interpretation on the isothermal ferroelectric transition, which may help to further clarify the intricate structure-property relationship in this important lead-free piezoelectric material and other related systems.

Development of lead-free dielectric ceramics with large recoverable energy storage density (Wrec), high energy storage efficiency (η) and wide usage temperature range is of great significance to improve the overall performance of power electronic devices. Despite the numerous research efforts, performance of existing lead-free dielectric ceramics is barely satisfactory. Herein, an effective strategy to achieve ultrahigh energy storage performance via nano-scale polarization mismatch and reconstruction is proposed. By developing solid solutions of A-site coupling and B-site coupling ferroelectrics, polarization mismatch and ultrahigh energy storage performance can be realized in intermediated compositions. It is demonstrated that ultrahigh energy storage performance with a η of 93% and a Wrec of 4.49 J/cm3 is achieved in the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 (0.6BT-0.4BMT) ceramic, which is a record high energy storage property in lead-free relaxor ferroelectric bulk ceramics. Excellent temperature stability with a variation of Wrec and η less than 5% is also realized in a wide temperature range from 30 °C to 170 °C. Such an ultrahigh energy storage performance not only verifies our strategy, but also makes the 0.6BT-0.4BMT ceramic a promising candidate material for energy storage. Moreover, of particular significance is that this work provides an effective method to design novel high performance dielectric ceramics for future energy storage devices.

The current–voltage (I–V) characterization was studied on the (111)-oriented BaTiO3 thin films on Pt-buffered Si substrates. The ferroelectric domains polarized downward had a smaller resistance and a better corresponding electrical property. An abnormal asymmetric switching was observed, which is similar to the memristive behavior at the pre-switching state. With increasing bias, the I–V curve under the positive bias tended to be saturated. The film showed a better endurance of the negative bias than the positive one. Such findings are promising for the potential utilization of barium titanate thin films as new type memristive memory application apart from the classic ferroelectric memory.

A giant electrocaloric effect (ECE) can be achieved in ferroelectric thin films, which demonstrates the applications of thin films in alternative cooling. However, electrocaloric thin films fabricated by conventional techniques, such as the pulsed laser deposition or sol-gel methods, may be limited by high costs, low yield and their dependence on substrates. In this study, we present a new bottom-up strategy to construct electrocaloric Ba

Lead free relaxor ferroelectrics have attracted continuing interest due to their outstanding and eco-friendly properties. In this paper, dielectric relaxation behavior of the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic (BT-40BMT), which is a typical lead free relaxor ferroelectric, is theoretically and experimentally investigated. At first, the observed dielectric relaxation was quantitatively characterized by a statistical model, indicating that the minority co-related polar nano regions (PNRs) dominate the total polarization. Kinetics of the PNRs were subsequently studied by micro-Raman measurements performed at various temperatures. Here, the relaxation of written domains formed by the piezoresponse force microscopy (PFM) tip-bias induced electric field was also studied, which describes the polarization retention performance of BT-40BMT. The absence of ferroelectric signal contribution in local switching was also confirmed by the contact mode Kelvin PFM technique, indicating the lack of local ferroelectricity. Moreover, the temperature insensitive energy storage property from 293 K to 443 K was obtained. High voltage pulsed discharge behavior was also investigated by using the pulsed current. A power density of 7.9 × 108 W/kg is obtained under a pulsed voltage of 50 kV. Combined with the fast discharge time, the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic is considered as a candidate material for high voltage pulse power applications.

We report a large electrocaloric efficiency of 0.029 K cm kV−1 at 303 K and in a wide operating temperature range of 293 K to 313 K in a lead-free Ba0.9Sr0.1(Ti0.9Zr0.1)0.95Sn0.05O3 ceramic by using direct electrocaloric effect (ECE) measurements. Sn4+ doping in Ba0.9Sr0.1Ti0.9Zr0.1O3 not only tunes the rhombohedral-to-paraelectric phase transition temperature to room temperature but also slightly widens the phase transition region, by slightly strengthening the diffuse character and maintaining its good ferroelectricity. Also, polar nanoregions embedded in the matrix facilitate polarization rotation because of a flat energy landscape associated with the relaxor-to-ferroelectric phase transition, inducing enhanced entropy changes and consequently excellent ECE performance.