Ferroelectric and Relaxor-Ferroelectric Phases Coexisting Boosts Energy Storage Performance in (Bi0.5Na0.5)TiO3-Based Ceramics.

With the intensification of the energy crisis, it is urgent to vigorously develop new environment-friendly energy storage materials. In this work, coexisting ferroelectric and relaxor-ferroelectric phases at a nanoscale were constructed in Sr(Zn1/3Nb2/3)O3 (SZN)-modified (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT) ceramics, simultaneously contributing to large polarization and breakdown electric field and giving rise to a superior energy storage performance. Herein, a high recoverable energy density (Wrec) of 5.0 J/cm3 with a conversion efficiency of 82% at 370 kV/cm, a practical discharged energy density (Wd) of 1.74 J/cm3 at 230 kV/cm, a large power density (PD) of 157.84 MW/cm3, and an ultrafast discharge speed (t0.9) of 40 ns were achieved in the 0.85BNBT-0.15SZN ceramics characterized by the coexistence of a rhombohedral-tetragonal phase (ferroelectric state) and a pseudo-cubic phase (relaxor-ferroelectric state). Furthermore, the 0.85BNBT-0.15SZN ceramics also exhibited excellent temperature stability (25-120 °C) and cycling stability (104 cycles) of their energy storage properties. These results demonstrate the great application potential of 0.85BNBT-0.15SZN ceramics in capacitive pulse energy storage devices.

Polymorphic Heterogeneous Polar Structure Enabled Superior Capacitive Energy Storage in Lead-Free Relaxor Ferroelectrics at Low Electric Field.

High-performance energy storage dielectrics capable of low/moderate field operation are vital in advanced electrical and electronic systems. However, in contrast to achievements in enhancing recoverable energy density (Wrec), the active realization of superior Wrec and energy efficiency (η) with giant energy-storage coefficient (Wrec/E) in low/moderate electric field (E) regions is much more challenging for dielectric materials. Herein, lead-free relaxor ferroelectrics are reported with giant Wrec/E designed with polymorphic heterogeneous polar structure. Following the guidance of Landau phenomenological theory and rational composition construction, the conceived (Bi0.5Na0.5)TiO3-based ternary solid solution that delivers giant Wrec/E of ≈0.0168 µC cm-2, high Wrec of ≈4.71 J cm-3 and high η of ≈93% under low E of 280 kV cm-1, accompanied by great stabilities against temperature/frequency/cycling number and excellent charging-discharging properties, which is ahead of most currently reported lead-free energy storage bulk ceramics measured at same E range. Atomistic observations reveal that the correlated coexisting local rhombohedral-tetragonal polar nanoregions embedded in the cubic matrix are constructed, which enables high polarization, minimized hysteresis, and significantly delayed polarization saturation concurrently, endowing giant Wrec/E along with high Wrec and η. These findings advance the superiority and feasibility of polymorphic nanodomains in designing highly efficient capacitors for low/moderate field-region practical applications.

Breaking the Mutual Constraint between Polarization and Voltage Resistance with Nanograined High-Entropy Ceramic.

Dielectric ceramics with a high energy storage capacity are key to advanced pulsed power capacitors. However, conventional materials face a mutual constraint between polarization strength and the breakdown strength bottleneck. To address this limitation, the concept of nanograined high-entropy ceramics is introduced in this work. By introducing a large number of constituent elements into the A-site of perovskite material lattice, high-entropy (Bi0.2K0.2Ba0.2Sr0.2Ca0.2)TiO3-0.2 'CuO relaxor ceramic with nanoscale grains have been successfully prepared, which breaks the mutual constraint between polarization strength and breakdown strength bottleneck and results a recoverable energy density (Wrec ∼ 6.86 J/cm3) and an efficiency (η ∼ 87.7%) at 670 kV/cm. Moreover, its excellent stability makes it potentially useful under a variety of extreme conditions, including at high temperatures and high/low frequencies. These obtained results demonstrate that this nanograined high-entropy lead-free perovskite ceramic has great potential for energy storage applications.

Effective Photocatalytic Ethanol Reforming into High-Value-Added Multicarbon Compound Coupled with H2 Production Over Pt-S3 Sites at PtSA -ZnIn2 S4 Interface.

Selective photocatalytic production of high-value acetaldehyde concurrently with H2 from bioethanol is an appealing approach to meet the urgent environment and energy issues. However, the difficult ethanol dehydrogenation and insufficient active sites for proton reduction within the catalysts, and the long spatial distance between these two sites always restrict their catalytic activity. Here, guided by the strong metal-substrate interaction effect, an atomic-level catalyst design strategy to construct Pt-S3 single atom on ZnIn2 S4 nanosheets (PtSA -ZIS) is demonstrated. As active center with optimized H adsorption energy to facilitate H2 evolution reaction, the unique Pt single atom also donates electrons to its neighboring S atoms with electron-enriched sites formed to activate the O─H bond in * CH3 CHOH and promote the desorption of * CH3 CHO. Thus, the synergy between Pt single atom and ZIS together will reduce the energy barrier for the ethanol oxidization to acetaldehyde, and also narrow the spatial distance for proton mass transfer. These features enable PtSA -ZIS photocatalyst to produce acetaldehyde with a selectivity of ≈100%, which will spontaneously transform into 1,1-diethoxyethane via acetalization to avoid volatilization. Meanwhile, a remarkable H2 evolution rate (184.4 µmol h-1 ) is achieved with a high apparent quantum efficiency of 10.50% at 400 nm.

Superb Energy Storage Capability for NaNbO3 -Based Ceramics Featuring Labyrinthine Submicro-Domains with Clustered Lattice Distortions.

Designing superb dielectric capacitors is valuable but challenging since achieving simultaneously large energy-storage (ES) density and high efficiency is difficult. Herein, the synergistic effect of grain refining, bandgap widening, and domain engineering is proposed to boost comprehensive ES properties by incorporating CaTiO3 into 0.92NaNbO3 -0.08BiNi0.67 Ta0.33 O3 matrix (as abbreviated NN-BNT-xCT). Apart from grain refining and bandgap widening, multiple local distortions embedded in labyrinthine submicro-domains, as indicated by diffraction-freckle splitting and ½-type superlattices, produce slush-like polar clusters for the NN-BNT-0.2CT ceramic, which should be ascribed to the coexisting P4bm, P21 ma, and Pnma2 phases. Consequently, a high recoverable ES density Wrec of ≈ 7.1 J cm-3 and a high efficiency η of ≈ 90% at 646 kV cm-1 is achieved for the NN-BNT-0.2CT ceramic. Such hierarchically polar structure is favorable to superb comprehensive ES properties, which provide a strategy for developing high-performance dielectric capacitors.

Superior Energy Storage Capability and Stability in Lead-Free Relaxors for Dielectric Capacitors Utilizing Nanoscale Polarization Heterogeneous Regions.

The development of high-performance lead-free dielectric ceramic capacitors is essential in the field of advanced electronics and electrical power systems. A huge challenge, however, is how to simultaneously realize large recoverable energy density (Wrec ), ultrahigh efficiency (η), and satisfactory temperature stability to effectuate next-generation high/pulsed power capacitors applications. Here, a strategy of utilizing nanoscale polarization heterogeneous regions is demonstrated for high-performance dielectric capacitors, showing comprehensive properties of large Wrec (≈6.39 J cm-3 ) and ultrahigh η (≈94.4%) at 700 kV cm-1 accompanied by excellent thermal endurance (20-160 °C), frequency stability (5-200 Hz), cycling reliability (1-105 cycles) at 500 kV cm-1 , and superior charging-discharging performance (discharge rate t0.9 ≈ 28.4 ns, power density PD ≈161.3 MW cm-3 ). The observations reveal that constructing the polarization heterogeneous regions in a linear dielectric to form novel relaxor ferroelectrics produces favorable microstructural characters, including extremely small polar nanoregions with high dynamics and multiphase coexistence and stable local structure symmetry, which enables large breakdown strength and ultralow polarization switching hysteresis, hence synergistically contributing to high-efficient capacitive energy storage. This study thus opens up a novel strategy to design lead-free dielectrics with comprehensive high-efficient energy storage performance for advanced pulsed power capacitors applications.

Synergy of a Stabilized Antiferroelectric Phase and Domain Engineering Boosting the Energy Storage Performance of NaNbO3-Based Relaxor Antiferroelectric Ceramics.

Relaxor antiferroelectric (AFE) ceramic capacitors have drawn growing attention in future advanced pulsed power devices for their superior energy storage performance. However, state of the art dielectric materials are restricted by desirable comprehensive energy-storage features, which have become a longstanding hurdle for actual capacitor applications. Here, we report that a large energy density Wrec of 5.52 J/cm3, high efficiency η of 83.3% at 560 kV/cm, high power density PD of 114.8 MW/cm3, ultrafast discharge rate t0.9 of 45 ns, and remarkable stability against temperature (30-140 °C)/frequency (5-200 Hz)/cycles (1-105) are simultaneously achieved in 0.7 NaNbO3-0.3 CaTiO3 relaxor AFE ceramics via the synergy of stabilized AFE R phase and domain engineering in combination with breakdown strength enhancement. The structural origin for these achievements is disclosed by probing the in situ microstructure evolution by means of the first-order reversal curve method, piezoelectric force microscopy, and Raman spectroscopy. The highly dynamic polar nanoregions and stabilized AFE R phase synergistically generate a linear-like and highly stable polarization field response over a wide temperature and field scope with concurrently improved energy density and efficiency. This work offers a new solution for designing high-performance next-generation pulsed power capacitors.

Simultaneously Realizing Superior Energy Storage Properties and Outstanding Charge-Discharge Performances in Tungsten Bronze-Based Ceramic for Capacitor Applications.

The development of lead-free ceramics with appropriate energy storage properties is essential for the successful practical application of advanced electronic devices. In this study, a site engineering strategy was proposed to concurrently decrease grain size, increase the band-gap, and enhance the relaxor nature in Ta-doped tungsten bronze ceramics (Sr2NaNb5-xTaxO15) for the improvement of the dielectric breakdown strength and the polarization difference. As a result, the ceramic with x = 1.5, that is, Sr2NaNb3.5Ta1.5O15, exhibited superior energy density (∼3.99 J/cm3) and outstanding energy efficiency (∼91.7%) (@380 kV/cm) as well as good thermal stability and remarkable fatigue endurance. In addition, the ceramic demonstrated an ultrashort discharge time (τ0.9 < 57 ns), a high discharge current density (925.8 A/cm2) along with a high power density (78.7 MW/cm3). The energy storage properties in combination with good stability achieved in this work indicate the powerful potential of Sr2NaNb5-xTaxO15 tungsten bronze ceramics for high-performance capacitor applications. This material can be considered as a complement to the widely studied perovskite-based relaxor ceramics and should be further investigated in the future.

Porous and hydrophobic graphene-based core-shell sponges for efficient removal of water contaminants.

Water pollution is a global environmental problem that has attracted great concern, and functional carbon nanomaterials are widely used in water treatment. Here, to optimize the removal performance of both oil/organic matter and dye molecules, we fabricated porous and hydrophobic core-shell sponges by growing graphene on three-dimensional stacked copper nanowires. The interconnected pores between the one-dimensional nanocore-shells construct the porous channels within the sponge, and the multilayered graphene shells equip the sponge with a water contact angle over 120° even under acidic and alkaline environments, which enables fast and efficient cleanup of oil on or under the water. The core-shell sponge can absorb oil or organic solvents with densities 40-90 times its own, and its oil-sorption capacity is much larger than those of other porous materials like activated carbon and loofah. On the other hand, the adsorption behavior of the core-shell sponge to dyes including methyl orange (MO) and malachite green (MG), also common water pollutants, was also measured. Dynamic adsorption of MG under cyclic compression demonstrated a higher adsorption rate than that in the static state, and an acidic environment was favorable for the adsorption of MO molecules. Finally, the adsorption isotherm for MO molecules was analyzed and fitted with the Langmuir model, and the adsorption kinetics were studied in depth as well.

Construction of hierarchical CoP@Ni2P core-shell nanoarrays for efficient electrocatalytic hydrogen evolution in alkaline solution.

Design and synthesis of non-noble electrocatalyst with controlled structure and composition for hydrogen evolution reaction (HER) are significant for large-scale water electrolysis. Here, an elegant multi-step templating strategy is developed for the fabrication of vertically aligned CoP@Ni2P nanowire-nanosheet architecture on Ni foam. Cobalt-carbonate hydroxides nanowires grown on Ni foam are first synthesized as the self-template. Afterward, a layer of amorphous Ni(OH)2 nanosheets is grown on the Co-based precursors through a chemical bath process, which is then transformed into the hierarchical CoP@Ni2P nanoarrays by a co-phosphatization treatment. Owing to the synergistic effect of the compositions and the advantages of the hierarchical heterostructures, the resulting hybrid electrocatalyst with dense heterointerfaces is revealed as an excellent HER catalyst, with a low overpotential of 101 mV at the current density of 10 mA cm-2, a relatively small Tafel slope of 79 mV dec-1, and favorable long-term stability of at least 20 h in 1 M KOH.

Remarkable capacitive performance in novel tungsten bronze ceramics.

In this study, novel lead-free Sr1.75Ca0.25NaNb5O15 tungsten bronze ceramics were designed for potential energy storage applications. A remarkable energy storage density (∼3.23 J cm-3) along with a high energy storage efficiency (∼88.2%) was obtained simultaneously at an applied electric field of 290 kV cm-1. Moreover, the ceramic also showed exceptional discharging performance including a fast discharge rate (τ0.9 < 70 ns), an ultrahigh discharge current density (1104 A cm-2) and a high power density (82.8 MW cm-3). The achieved capacitive performance in this work indicates the great potential of the designed novel tungsten bronze ceramic for energy storage applications.

Energy Manipulation in Lanthanide-Doped Core-Shell Nanoparticles for Tunable Dual-Mode Luminescence toward Advanced Anti-Counterfeiting.

Developing advanced luminescent materials and techniques is of significant importance for anti-counterfeiting applications, and remains a huge challenge. In this work, a new and efficient approach for achieving efficient dual-mode luminescence with tunable color outputs via Gd3+ -mediated interfacial energy transfer, Ce3+ -assisted cross-relaxation, and core-shell nanostructuring strategy is reported. The introduction of Ce3+ into the inner core not only serves the regulation of upconversion emission, but also facilitates the ultraviolet photon harvesting and subsequent energy transfer to downshifting (DS) activators in the outer shell layer. Furthermore, the construction of the core@shell nanoarchitecture enables the spatial separation of upconverting activators and DS centers, which greatly suppresses their adverse cross-relaxation processes. Consequently, efficient and multicolor-tunable dual-mode emissions can be simultaneously observed in the pre-designed NaGdF4 :Yb/Ho/Ce@NaYF4 :X (X = Eu, Tb, Sm, Dy) core-shell nanostructures under 254 nm ultraviolet light and 980 nm laser excitation. The proof-of-concept experiment demonstrates that 2D-encoded patterns based on dual-mode emitting nanomaterials are very promising for anti-counterfeiting applications. It is believed that this preliminary study will advance the development of the fluorescent materials for potential applications in anti-counterfeiting and optical multiplexing.

Integrating chemical engineering and crystallographic texturing design strategy for the realization of practically viable lead-free sodium bismuth titanate-based incipient piezoceramics.

Off-resonance actuators utilizing lead-free incipient piezoelectric materials have recently gained extensive attention because of their exceptionally high electromechanical strain. However, current incipient piezoelectric materials have three critical challenges, namely, high driving field required for producing potentially high strains, high frequency dependence, and relatively poor fatigue resistance, which seriously restrict the implementation of lead-free incipient piezoelectrics in high-efficiency actuator applications. Herein, we demonstrate that the integration of chemical engineering and crystallographic texturing design strategies into a Bi0.5Na0.5TiO3-based system provides a highly effective approach to address these challenges. Novel 〈00l〉-oriented 0.97(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-0.03NN, as an exemplary incipient piezoelectric ceramic, was fabricated to experimentally demonstrate this design concept. A low field-driven large strain response (∼0.32% at 50 kV cm-1, ∼0.46% at 75 kV cm-1), excellent frequency dependence (∼0.42% at 65 kV cm-1, <5% variation from 0.1 Hz to 100 Hz), and superior fatigue endurance (S > 0.4%, <10% change up to 105 cycles) were simultaneously achieved in the manufactured textured ceramic, which is superior to that reported previously in most lead-free perovskite ceramics. These outstanding actuator performances can be mainly ascribed to the considerably easy ergodic relaxor to ferroelectric phase transition due to the formation of an oriented microstructure, which promotes domain switching and mobility, as confirmed by PFM measurements. This study offers a feasible and reproducible design methodology, i.e., chemical engineering and crystallographic texturing, to develop viable incipient piezoceramics and will guide future efforts in this field.

Efficient dual-mode luminescence from lanthanide-doped core-shell nanoarchitecture for anti-counterfeiting applications.

Fluorescent anti-counterfeiting technique is generally based on the development of luminescent materials, which generally exhibit single-mode emissions under single-wavelength excitation, thus resulting in a poor anti-fake effect. To improve the anti-forgery performance of fluorescent anti-counterfeiting approaches, dual-mode luminescent nanoparticles with the form of a ß-NaGdF4:Yb/Ho/Ce@ß-NaYF4:Tb/Eu core-shell structure have been skillfully designed and synthesized by a co-precipitation strategy. Through the cross-relaxation process between Ce3+ and Ho3+ ions in the inner core region, the up-conversion luminescence colors of the as-synthesized samples can be turned from green to yellow and finally to red when adjusting the dopant concentration of Ce3+ in the core. By selecting Ce3+ as the sensitizer for harvesting the energy of incident ultraviolet (UV) light and introducing Gd3+ as the ideal intermediate for subsequent energy migration, the down-converting emission colors of the as-obtained samples are also regulated from green to red via a Gd3+-assisted interface energy transfer processes (Ce3+ → Gd3+ → Tb3+, Ce3+ → Gd3+ → Tb3+ → Eu3+). Consequently, dual-mode luminescence with multi-color outputs can be achieved in the pre-designed core-shell nanostructure under the excitation of a 980 nm near-infrared laser and 254 nm UV light. The designed nanoarchitecture with bright dual-mode emissions and tunable colors greatly improves the ability of modern anti-counterfeiting, demonstrating its promising applications in anti-fake and optical multiplexing.

Few-Layer Black Phosphorus Nanosheets: A Metal-Free Cocatalyst for Photocatalytic Nitrogen Fixation.

Exploiting an appropriate strategy to prepare fine crystal quality black phosphorus nanosheet (BPNS) catalyst is a major challenge for its practical application in catalysis. Herein, we address this challenge by developing a rapid electrochemical expansion strategy for scale preparation of fine crystal quality BPNSs from bulk black phosphorus, which was demonstrated to be an active cocatalyst for photocatalytic nitrogen fixation in the presence of CdS as a photocatalyst. The transient photocurrent and charge density studies show that the BPNSs can efficiently accelerate charge separation of CdS, leading to the enhanced photocatalytic activities of BPNS/CdS nanocomposites for nitrogen fixation. The 1.5% BPNS/CdS photocatalyst exhibits the highest photocatalytic activity for nitrogen fixation with an NH3 evolution rate of 57.64 µmol·L-1·h-1. This study not only affords a rapid and simple strategy for scale synthesis of fine crystal quality BPNSs but also provides new insights into the design and development of black phosphorus-based materials as low-cost metal-free cocatalysts for photocatalytic nitrogen fixation.

Tailoring frequency-insensitive large field-induced strain and energy storage properties in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-modified (Bi0.5Na0.5)TiO3 lead-free ceramics.

Lead-free (Bi0.5Na0.5)TiO3-based relaxor ferroelectrics are attracting growing research interest due to their very large field-induced strain response and excellent energy storage performance. While extensive explorations have been made of these performances separately, being able to optimize both field-induced strain and energy storage performance of polycrystalline materials together, and hence achieve a synergistic result, would also be highly desirable for their practical applications. Herein, lead-free relaxor-ferroelectric (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-modified (Bi0.5Na0.5)TiO3 (BNT-BCZT) ceramics were designed and demonstrated to be feasible candidates for both actuator and pulsed power capacitors. Optimal field-induced strain performances were realized in 0.92BNT-0.08BCZT ceramics with not only a high strain of 0.46% but also an impressive frequency stability (0.5 Hz-100 Hz), superior to those of other reported BNT-based materials under a similar frequency range. Moreover, the 0.5BNT-0.5BCZT compositions in the complete ER region delivered a relatively high Wrec of 0.95 J cm-3 and η of 69%, while still remaining insensitive to changes in temperature, frequency, and cycle number. More importantly, a short discharge time (of ∼0.41 µs) was also measured for this composition. Introducing BCZT into the composition was found to promote a non-ergodic-to-ergodic relaxor (NR-ER) phase transition and the formation of dynamic polar nanoregions (PNRs), generating the high strain responses and superior energy storage performances of the given compositions. These features may offer a new strategy to simultaneously tailor lead-free relaxor ferroelectrics toward high field-induced strain and superior energy storage performance for ceramics actuators and capacitor applications.

Lead-free BNT-based composite materials: enhanced depolarization temperature and electromechanical behavior.

The development of (Bi0.5Na0.5)TiO3-based solid solutions with both high depolarization temperature Td and excellent piezoelectric and electromechanical properties for practical application is intractable because improved thermal stability is usually accompanied by a deterioration in piezoelectric and electromechanical performance. Herein, we report a 0-3 type 0.93(Bi0.5Na0.5)TiO3-0.07BaTiO3 : 30 mol%ZnO composite (BNT-7BT : 0.3ZnO), in which the ZnO nanoparticles exist in two forms, to resolve the abovementioned long-standing obstacle. In this composite, Zn ions fill the boundaries of BNT-7BT grains, and residual Zn ions diffuse into the BNT-7BT lattice, as confirmed by XRD, Raman spectroscopy, and microstructure analysis. The BNT-7BT composite ceramics with a 0-3 type connectivity exhibited enhanced frequency-dependent electromechanical properties, fatigue characteristics, and thermal stabilities. More importantly, low poling field-driven large piezoelectric properties were observed for the composite ceramics as compared to the case of the pure BNT-7BT solid solution. A mechanism related to the ZnO-driven phase transition from the rhombohedral to tetragonal phase and built-in electric field to partially compensate the depolarization field was proposed to explain the achieved outstanding piezoelectric performance. This is the first time that the thermal stability, electromechanical behavior, and low poling field-driven high piezoelectric performance of BNT-based ceramics have been simultaneously optimized. Thus, our study provides a referential methodology to achieve novel piezoceramics with excellent piezoelectricity by composite engineering and opens up a new development window for the utilization of conventional BNT-based and other lead-free ceramics in practical applications.

Phase evolution and correlation between tolerance factor and electromechanical properties in BNT-based ternary perovskite compounds with calculated end-member Bi(Me0.5Ti0.5)O3 (Me = Zn, Mg, Ni, Co).

In this work, the structure of end-member Bi(Me0.5Ti0.5)O3 (Me = Zn, Ni, Mg, Co) was calculated through a first-principles method and lead-free piezoelectric ternary systems (0.94 -x)(Bi0.5Na0.5)TiO3-0.06BaTiO3-xBi(Me0.5Ti0.5)O3 (Me = Zn, Ni, Mg, Co) (BNT-BT-Bi(Me0.5Ti0.5)O3) were designed to achieve a large strain response for actuator applications. Composition-driven phase transition characteristics and the resulting associated piezoelectric and electromechanical properties were systematically investigated, and schematic phase diagrams were constructed. XRD measurements, Raman spectra analysis and temperature-dependent polarization and strain hysteresis loops indicate that Bi(Me0.5Ti0.5)O3 substitution induces a phase transformation from a ferroelectric rhombohedral to an ergodic relaxor pseudo-cubic phase, accounting for the large strain response (>0.3%) with a high normalized strain Smax/Emax (≥550 pm V(-1)) at around the corresponding critical composition in the vicinity of room temperature. In addition, correlations between the tolerance factor t of the added end-member, the calculated tetragonality and the morphotropic phase boundary (MPB) composition were sought. In comparison to other reported BNT-based systems, there is a noticeable correlation between the MPB composition and the calculated tetragonality of the end-member Bi(Me0.5Ti0.5)O3, and the t value corresponding to the formation of the MPB composition is approximately 0.981 in the present ternary system with low tolerance factor end-members. As a result, we believe that the general correlations and design principles obtained from the present comprehensive research will be effective to predict the approximate MPB region quickly in BNT-based ceramics with an excellent actuating performance.

Composition- and temperature-driven phase transition characteristics and associated electromechanical properties in Bi0.5Na0.5TiO3-based lead-free ceramics.

In this study, a lead-free ceramic system comprising (0.94 - x)Bi0.5Na0.5TiO3-0.06BaTiO3-xBi(Zn0.5Ti0.5)O3 (BNT-BT-BZT) was designed and prepared by a conventional solid-state reaction method. The effect of the addition of BZT on the phase transition characteristics and associated electromechanical properties of BNT-BT was systematically discussed and a schematic phase diagram was established. The addition of BZT had a strong impact on the phase transition as well as the strain and piezoelectric activity. The phase coexistence, which involves ferroelectric rhombohedral-relaxor pseudocubic phases, can be driven by modification with BZT and increases in temperature and can be confirmed by XRD measurements, analysis of Raman spectra and temperature-dependent changes in polarization and strain hysteresis loops. Accompanied by a shift in the ferroelectric-to-relaxor temperature TF-R to below room temperature on the addition of BZT, a compositionally induced ferroelectric-to-relaxor phase transition occurred, which gave rise to a large strain of 0.33% with a normalized strain Smax/Emax of 550 pm V(-1) at the critical BZT content x of 0.0275. The results were closely correlated with the composition and dependence on temperature of the phase transition, which significantly influenced the electromechanical properties, and the origin of the large strain observed in the present system was also addressed in detail. As a result, the design principles provided in this study open the possibility of obtaining BNT-based lead-free ceramics with enhanced electromechanical properties for actuator applications.

New Eu(3+)-activated perovskite La(0.5)Na(0.5)TiO3 phosphors in glass for warm white light emitting diodes.

With an increasing demand for high-power warm white light emitting diodes (w-LEDs), the discovery of efficient red-emitting inorganic color converters is in great demand. Herein, a novel perovskite La0.5Na0.5TiO3:Eu(3+) red-emitting phosphor with excellent thermal stability and high quantum efficiency has been successfully synthesized by a traditional solid-state reaction. Then, the developed La0.5Na0.5TiO3:Eu(3+) red phosphor and commercial YAG:Ce(3+) yellow phosphor were incorporated into an innovatively designed low-melting glass. Impressively, the destruction of La0.5Na0.5TiO3:Eu(3+) and YAG:Ce(3+) phosphor particles during glass melting was quite low. Remarkably, the fabricated w-LEDs using an InGaN-based blue chip combined with Phosphor in Glass (PiG) plates exhibited an improved chromaticity feature and superior optical performance. Through simply adjusting the content of red phosphors in the PiG, the correlated color temperature of the PiG-based w-LEDs evolved from cool white (6771 K) to warm white (4417 K) and the color rendering index increased from 73.4 to 86.4. Moreover, the PiG-based warm w-LEDs presented superior thermal stability.