Boosting tetracycline degradation of BaTiO3-based piezo-catalysts via modulating phase boundary and band structure.

Piezoelectric catalysis, which converts mechanical energy into chemical activity, has important applications in environmental remediation. However, the piezo-catalytic activity of various piezoelectric materials is limited by the weak piezoelectricity as well as the mismatched band-gap, leading to inefficient electron-hole pair generation and difficult carrier migration. Here, a simple strategy combining phase boundary and energy band structure modulation was innovatively proposed to enhance the piezo-catalytic activity of BaTiO3 ferroelectric by Ce ions selecting different doping sites. Thanks to the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) phases effectively flattened the Gibbs free-energy and thus enhanced the piezoelectric activity, as well as suitable energy bandwidth facilitating the carrier migration were realized in the B-sites doped Ba(Ti0.95Ce0.05)O3. The degradation rate constant k of tetracycline (TC) was high to 30.56 × 10-3 min-1, which was 2.03 times higher than that of pure BaTiO3 and superior to most representative lead-free perovskite piezoelectric materials. Theoretical calculations validated that the charge density and high O2 and OH- adsorption energy on the Ba(Ti0.95Ce0.05)O3 surface promoted more efficient •O2- and •OH radicals conversion and bettered response to piezo-catalytic reaction. This work is important to design high-performance piezo-catalysts by synergistic regulation of phase boundary and energy band structure in perovskite materials for long-term antibiotic tetracycline removal.

Dual-coupling effect enables a high-performance self-powered UV photodetector.

Self-powered ultraviolet photodetectors generally operate by utilizing the built-in electric field within heterojunctions or Schottky junctions. However, the effectiveness of self-powered detection is severely limited by the weak built-in electric field. Hence, advances in modulating the built-in electric field within heterojunctions are crucial for performance breakthroughs. Here, we suggest a method to enhance the built-in electric field by taking advantage of the dual-coupling effect between heterojunction and the self-polarization field of ferroelectrics. Under zero bias, the fabricated AgNWs/TiO2/PZT/GaN device achieves a responsivity of 184.31 mA/W and a specific detectivity of 1.7 × 1013 Jones, with an on/off ratio of 8.2 × 106 and rise/decay times reaching 0.16 ms/0.98 ms, respectively. The outstanding properties are primarily attributed to the substantial self-polarization of PZT induced by the p-GaN and the subsequent enhancement of the built-in electric field of the TiO2/PZT heterojunction. Under UV illumination, the dual coupling of the enhanced heterojunction and the self-polarizing field synergistically boost the photo-generated carrier separation and transport, leading to breakthroughs in ferroelectric-based self-powered photodetectors.

Fast-speed, Highly Sensitive, Flexible Humidity Sensors Based on a Printable Composite of Carbon Nanotubes and Hydrophilic Polymers.

Carbon nanotubes (CNTs) are a promising material for humidity sensors and wearable electronics due to their solution capability, good flexibility, and high conductivity. However, the performance of CNT-based humidity sensors is limited by their low sensitivity and slow response. Herein CNTs and hydrophilic polymers were mixed to form a composite. The hydrophilicity of the polymers and the network structure of the CNTs empowered the humidity sensors with a high response of 171% and a fast response/recovery time of 23 s/10 s. Owing to the sticky and flexible polymers, the humidity sensors showed strong adhesion to the PET substrate and exhibited outstanding bending durability. Furthermore, the flexible humidity sensor was applied to monitor human breathing and detect finger movements and handshaking.

B-Site Nanoscale-Ordered Structure Enables Ultra-High Tunable Performance.

Tunable devices constructed by ferroelectric thin films are often desired to possess a low dielectric loss while maintainging a high dielectric tunability over a broad operating temperature range in applications, for example, resonators, filters, or phase shifters. However, it is difficult to simultaneously achieve these characteristics by traditional strategies, such as doping and strain modifying. Here, we demonstrate that the dielectric tunability of the sol-gel-prepared Pb(Sc1/2Nb1/2)0.9(Mg1/3Nb2/3)0.1O3 (PSNMN) thin film can be almost doubled from ~47% to ~80.0% (at 10 kHz) at a low electric field (~530 kV/cm), and the dielectric loss can be sharply reduced by more than an order of magnitude, from ~0.50 to ~0.037 (at 1 kHz) when the thin film was annealed in air at 650°C for 15 h under the help of an atmosphere-compensating-block (ACB) made from the proto-PSNMN gel. Moreover, the PSNMN thin film annealed with ACB also exhibited an extremely high thermally-stable dielectric tunability in an ultrabroad temperature range (>130 K), which could be attributed to the Maxwell-Wagner (MW) effect generated by the interface between the PSNMN disordered matrix and the B-site nanoscale-ordered structure formed during the long-term annealing process. The reduced dielectric loss is mainly benefited from the reduced concentration of oxygen vacancy and the possible MW effects, and the enhanced dielectric tunability could be ascribed to the weaker domain-pinning effect by oxygen vacancy. The breakthrough provides a new universal strategy to achieve utrahigh tunable performance in A(B'1/2B"1/2)O3 ferroelectric thin films with a B-site nanoscale-ordered structure, meanwhile it paves the way for ultraintergrated tunable thin-film-devices with great phase shifter performance in practical applications.

Bimodal-Structured 0.9KNbO3-0.1BaTiO3 Solid Solutions with Highly Enhanced Electrocaloric Effect at Room Temperature.

0.9KNbO3-0.1BaTiO3 ceramics, with a bimodal grain size distribution and typical tetragonal perovskite structure at room temperature, were prepared by using an induced abnormal grain growth (IAGG) method at a relatively low sintering temperature. In this bimodal grain size distribution structure, the extra-large grains (~10-50 µm) were evolved from the micron-sized filler powders, and the fine grains (~0.05-0.35 µm) were derived from the sol precursor matrix. The 0.9KNbO3-0.1BaTiO3 ceramics exhibit relaxor-like behavior with a diffused phase transition near room temperature, as confirmed by the presence of the polar nanodomain regions revealed through high resolution transmission electron microscope analyses. A large room-temperature electrocaloric effect (ECE) was observed, with an adiabatic temperature drop (ΔT) of 1.5 K, an isothermal entropy change (ΔS) of 2.48 J·kg-1·K-1, and high ECE strengths of |ΔT/ΔE| = 1.50 × 10-6 K·m·V-1 and ΔS/ΔE = 2.48 × 10-6 J·m·kg-1·K-1·V-1 (directly measured at E = 1.0 MV·m-1). These greatly enhanced ECEs demonstrate that our simple IAGG method is highly appreciated for synthesizing high-performance electrocaloric materials for efficient cooling devices.

Tunable Green Light-Emitting CsPbBr3 Based Perovskite-Nanocrystals-in-Glass Flexible Film Enables Production of Stable Backlight Display.

Despite recent advances in producing perovskite-nanocrystals-in-glass (PNG) for display application, it remains challenging to achieve ultrapure and large-area CsPbBr3 PNG-based flexible films with tunable green emission. Herein, we report a facile strategy to produce flexible film containing CsPbBr3 PNG. Specifically, the achievement of CsPbBr3 PNG with tunable green emissions (517-528 nm) is realized by elaborate regulation of the glass precursor concentration and thermal treatment temperature by an in situ growth method. With the integration of red-light-emitting CsPbBrxI3-x PNG powder, the color gamut of as-prepared white-light-emitting sources can cover up to 126.27% of the NTSC 1953 standard and 93.9% of the Rec. 2020 standard. Notably, flexible and large-area white-light-emitting films can be readily obtained by sandwiching and gluing mixed PNG powders between two layers of hydrophobic and transparent PET films. Intriguingly, as-prepared PNG films exhibit excellent hydrothermal, photostability, and long-term operation stability, making them promising for practical ultrahigh-definition displays.

Strategy of Extra Zr Doping on the Enhancement of Thermoelectric Performance for TiZrxNiSn Synthesized by a Modified Solid-State Reaction.

Half-Heusler alloys, which possess the advantages of high thermal stability, a large power factor, and good mechanical property, have been attracting increasing interest in mid-temperature thermoelectric applications. In this work, extra Zr-doped TiZrxNiSn samples were successfully prepared by a modified solid-state reaction followed by spark plasma sintering. It demonstrates that extra Zr doping could not only improve the power factor on account of an increase in the Seebeck coefficient but also suppress the lattice thermal conductivity originated from the strengthened phonon scattering by the superlattice nanodomains and the secondary nanoparticles. As a consequence, an increased power factor of 3.29 mW m-1 K-2 and a decreased lattice thermal conductivity of 1.74 W m-1 K-1 are achieved in TiZr0.015NiSn, leading to a peak ZT as high as 0.88 at 773 K and an average ZT value up to 0.62 in the temperature range of 373-773 K. This work gives guidance for optimizing the thermoelectric performance of TiNiSn-based alloys by modulating the microstructures on the secondary nanophases and superlattice nanodomains.

Energy Storage and Electrocaloric Cooling Performance of Advanced Dielectrics.

Dielectric capacitors are widely used in pulse power systems, electric vehicles, aerospace, and defense technology as they are crucial for electronic components. Compact, lightweight, and diversified designs of electronic components are prerequisites for dielectric capacitors. Additionally, wide temperature stability and high energy storage density are equally important for dielectric materials. Ferroelectric materials, as special (spontaneously polarized) dielectric materials, show great potential in the field of pulse power capacitors having high dielectric breakdown strength, high polarization, low-temperature dependence and high energy storage density. The first part of this review briefly introduces dielectric materials and their energy storage performance. The second part elaborates performance characteristics of various ferroelectric materials in energy storage and refrigeration based on electrocaloric effect and briefly shed light on advantages and disadvantages of various common ferroelectric materials. Especially, we summarize the polarization effects of underlying substrates (such as GaN and Si) on the performance characteristics of ferroelectric materials. Finally, the review will be concluded with an outlook, discussing current challenges in the field of dielectric materials and prospective opportunities to assess their future progress.

Realizing a High ZT of 1.6 in N-Type Mg3Sb2-Based Zintl Compounds through Mn and Se Codoping.

Mg3Sb2-based compounds by virtue of nontoxicity and low-cost have become a promising class of candidates for midtemperature thermoelectric power generation. Here, we successfully fabricated n-type Mg3Sb2-based materials using an inexpensive and efficient approach of one-step ball milling and spark plasma sintering, and demonstrate that a complementary and favorable effect of multiple elements coalloying/-doping leads to an excellent thermoelectric performance. The intrinsic p-type conducting behavior for Mg3Sb2 could be changed to n-type through Bi and Se coalloying on Sb sublattices with excess Mg, resulting from the suppression of Mg vacancies and the formation of Mg interstitial. Furthermore, Mn doping on Mg sublattices could soften the chemical bonds, leading to the increase of carrier mobility and concentration simultaneously. Additionally, multielement coalloying/-doping could significantly increase the lattice disorder, which undoubtedly strengthens the phonon scattering and readily results in a suppressed lattice thermal conductivity. As a result, a highest ZT value of 1.6 at 723 K and an average ZT value up to 1.1 were obtained in the temperature range of 323-723 K in the Mg3.18Mn0.02Sb1.5Bi0.49Se0.01 sample, which is one of the highest values among the Te free Mg3Sb2. This work could give guidance for improving the thermoelectric performance of Zintl phase materials or even others using the multielement codoping/-alloying strategy.

Dielectric and Energy Storage Properties of Ba(1-x)CaxZryTi(1-y)O3 (BCZT): A Review.

The Ba(1-x)CaxZryTi(1-y)O3 (BCZT), a lead-free ceramic material, has attracted the scientific community since 2009 due to its large piezoelectric coefficient and resulting high dielectric permittivity. This perovskite material is a characteristic dielectric material for the pulsed power capacitors industry currently, which in turn leads to devices for effective storage and supply of electric energy. After this remarkable achievement in the area of lead-free piezoelectric ceramics, the researchers are exploring both the bulk as well as thin films of this perovskite material. It is observed that the thin film of this materials have outstandingly high power densities and high energy densities which is suitable for electrochemical supercapacitor applications. From a functional materials point of view this material has also gained attention in multiferroic composite material as the ferroelectric constituent of these composites and has provided extraordinary electric properties. This article presents a review on the relevant scientific advancements that have been made by using the BCZT materials for electric energy storage applications by optimizing its dielectric properties. The article starts with a BCZT introduction and discussion of the need of this material for high energy density capacitors, followed by different synthesis techniques and the effect on dielectric properties of doping different materials in BCZT. The advantages of thin film BCZT material over bulk counterparts are also discussed and its use as one of the constituents of mutiferroic composites is also presented. Finally, it summarizes the future prospects of this material followed by the conclusions.

Facile Synthesis of Ultrahigh-Surface-Area Hollow Carbon Nanospheres and their Application in Lithium-Sulfur Batteries.

Hollow carbon nanospheres (HCNs) with specific surface areas up to 2949 m2 g-1 and pore volume up to 2.9 cm3 g-1 were successfully synthesized from polyaniline-co-polypyrrole hollow nanospheres by carbonization and CO2 activation. The cavity diameter and wall thickness of HCNs can be easily controlled by activation time. Owing to their large inner cavity and enclosed structure, HCNs are desirable carriers for encapsulating sulfur. To better understand the effects of pore characteristics and sulfur contents on the performances of lithium-sulfur batteries, three composites of HCNs and sulfur are prepared and studied in detail. The composites of HCNs with moderate specific surface areas and suitable sulfur content present a better performance. The first discharge capacity of this composite reaches 1401 mAh g-1 at 0.2 C. Even after 200 cycles, the discharge capacity remains at 626 mAh g-1 .

Integration of c-axis oriented Bi3.15Nd0.85Ti2.95Hf0.05O12/La0.67Sr0.33MnO3 ferromagnetic-ferroelectric composite film on Si substrate.

A La0.67Sr0.33MnO3 (LSMO) ferromagnetic layer and a Nd3+/Hf4+ co-substituted Bi4Ti3O12 (Bi3.15Nd0.85Ti3-xHfxO12 (BNTHx, x = 0, 0.025, 0.05, 0.1 and 0.15)) ferroelectric layer were successively deposited onto the (00 l)-oriented LaNiO3 (LNO) layer buffered (001) Si substrate via all chemical solution deposition (CSD) method. As a result, the BNTHx/LSMO ferromagnetic-ferroelectric composite films integrated on Si substrate exhibit high c-axis orientation. The Nd3+/Hf4+ co-substituted BNTHx films have the lower leakage current and the better ferroelectric properties than the mono-substituted Bi4Ti3O12 (Bi3.15Nd0.85Ti3O12 and Bi4Ti2.95Hf0.05O12) films. In particular, the BNTH0.05/LSMO/LNO film has the lowest leakage current density of 2.5 × 10-7 A/cm2 at 200 kV/cm, and the highest remnant polarization (Pr) of 27.3 µC/cm2. The BNTH0.05/LSMO/LNO composite film also exhibits the soft ferromagnetism characteristics with a high saturated magnetization of 258 emu/cm3 at 300 K, and the excellent magnetoelectric (ME) effect. The variations of ME voltage coefficient α E values with DC bias magnetic field H bias shows that the BNTH0.05/LSMO/LNO film has the high α E value at near zero H bias. Moreover, at H bias = 0 Oe, the α E value gradually increases from zero with the increasing of the AC magnetic field frequency, and eventually reaches about 18.9 V/cm·Oe at 100 kHz, suggesting the existence of self-biased ME effect.

Large nonlinear dielectric behavior in BaTi1-xSnxO3.

BaTi1-xSnxO3 (BTSn, 0 ≤ x ≤ 0.30) ceramics were prepared by both the conventional sintering (CS) and sparking plasma sintering (SPS). Composition, temperature and grain size dependences of the nonlinear dielectric behaviors were systematically studied. BTSn was found to have especially large tunability (≥90%), which is larger than most other Pb-free systems, and is comparable to Pb-based relaxors. The high dielectric tunability in BTSn is attributed to its specific domain structures. Besides, temperature dependent tunability of BTSn presents a dispersed behavior and the dispersion is enhanced with the increase of Sn4+ concentrations, which is explained by the compositional fluctuation model.

Understanding Phonon Scattering by Nanoprecipitates in Potassium-Doped Lead Chalcogenides.

We present a comprehensive experimental and theoretical study of phonon scattering by nanoprecipitates in potassium-doped PbTe, PbSe, and PbS. We highlight the role of the precipitate size distribution measured by microscopy, whose tuning allows for thermal conductivities lower than the limit achievable with a single size. The correlation between the size distribution and the contributions to thermal conductivity from phonons in different frequency ranges provides a physical basis to the experimentally measured thermal conductivities, and a criterion to estimate the lowest achievable thermal conductivity. The results have clear implications for efficiency enhancements in nanostructured bulk thermoelectrics.

Large Energy Storage Density and High Thermal Stability in a Highly Textured (111)-Oriented Pb0.8Ba0.2ZrO3 Relaxor Thin Film with the Coexistence of Antiferroelectric and Ferroelectric Phases.

A highly textured (111)-oriented Pb0.8Ba0.2ZrO3 (PBZ) relaxor thin film with the coexistence of antiferroelectric (AFE) and ferroelectric (FE) phases was prepared on a Pt/TiOx/SiO2/Si(100) substrate by using a sol-gel method. A large recoverable energy storage density of 40.18 J/cm(3) along with an efficiency of 64.1% was achieved at room temperature. Over a wide temperature range of 250 K (from room temperature to 523 K), the variation of the energy density is within 5%, indicating a high thermal stability. The high energy storage performance was endowed by a large dielectric breakdown strength, great relaxor dispersion, highly textured orientation, and the coexistence of FE and AFE phases. The PBZ thin film is believed to be an attractive material for applications in energy storage systems over a wide temperature range.