Effect of the element ratio in the doping component on the properties of 0.975(0.8Bi1/2Na1/2TiO3–0.2Bi1/2K1/2TiO3)–0.025Bix/3Mgy/3Nbz/3O3 ceramics

A new series of ternary perovskite 0.975(0.8Bi Na TiO –0.2Bi K TiO )–0.025Bi Mg Nb O (BNT–BKT–BMN, BMN‐xyz) ceramics were designed and synthesized. The effect of the element ratio in the doping component BMN on the strain, ferroelectric, piezoelectric, and dielectric properties of the BNT–BKT matrix were studied. The BMN‐430 composition without Nb element exhibits the typical features of non‐ergodic relaxor, which is characterized by a higher piezoelectric coefficient d and a butterfly‐shaped strain curve with negative strain. The introduction of trace Nb can significantly enhance the ergodicity of the system, reflecting in the high positive strain response and strain coefficient (d33∗>750pm/V) of BMN‐321 composition. In contrast, there is no significant difference in the properties between the presence and absence of Mg element. The temperature‐dependent electrical behaviors of BMN‐xyz ceramics were analyzed based on impedance spectroscopy. This study may be helpful to the design of the chemical modification strategy for the BNT‐based relaxor ferroelectrics. [Figure not available: see fulltext.] 1/2 1/2 3 1/2 1/2 3 x /3 y /3 z /3 3 3

Multilayered ZnO Nanosheets with 3D Porous Architectures: Synthesis and Gas Sensing Application

Multilayered ZnO nanosheets with three-dimensional (3D) porous architectures were synthesized by calcining a layered precursor of zinc hydroxide carbonate. The structural properties were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction techniques. It was observed that the concentration of the urea was the key parameter determining the final morphology. Room-temperature photoluminescence data showed interesting optical properties of the ZnO architectures. Gas sensing tests showed that these 3D porous ZnO architectures were highly promising for gas sensor applications, as the gas diffusion and mass transportation in sensing materials were significantly enhanced by their unique structures. Our results indicate that the 3D porous ZnO nanosheets have potential applications in fabricating optoelectrical devices and gas sensors

Structure, Phase Transition Behaviors and Electrical Properties of Nd Substituted Aurivillius Polycrystallines Na_0.5Nd_<i>x</i>Bi_{2.5–<i>x</i>}Nb₂O₉ (<i>x</i> = 0.1, 0.2, 0.3, and 0.5)

New high temperature Aurivillius piezoelectrics Na_0.5Nd_<i>x</i>Bi_{2.5–<i>x</i>}Nb₂O₉ (NDBN<i>x</i>, <i>x</i> = 0.1, 0.2, 0.3, and 0.5) with Nd substitution for Bi at the A site were synthesized using a solid state reaction process. Crystal structures of NDBN0.2 and NDBN0.5 were refined with the Rietveld method with powder X-ray diffraction, and they crystallized in the orthorhombic space group <i>A</i>2₁<i>am</i> [<i>a</i> = 5.48558(8) Å, <i>b</i> = 5.46326(9) Å, <i>c</i> = 24.8940(4) Å, and <i>Z</i> = 4 for NDBN0.2 and <i>a</i> = 5.46872(5) Å, <i>b</i> = 5.46730(5) Å, <i>c</i> = 24.80723(25) Å, and <i>Z</i> = 4 for NDBN0.5], at room temperature. The refinement results and Raman spectroscopy of NDBN<i>x</i> verified that Nd occupied both the A site in the perovskite layers and the cation site in the (Bi₂O₂)²⁺ layers. The Nd substitution induced an enhancement in cation disordering between the A site and the (Bi₂O₂)²⁺ layer and an increase in the degree of the relaxation behavior for NDBN<i>x</i>. The ferroelectric to paraelectric phase transition temperature (<i>T</i>_c) of NDBN<i>x</i> ranged from 735 to 764 °C. Furthermore, the isovalent substitution of Nd for Bi had a great influence on microstructure (grain size and shape), defect concentration (mainly oxygen vacancies), preferred grain orientation (texture), and distortion of the octahedron. The coaction between these effects determined the structure characteristics, phase transition behaviors, and electrical properties of NDBN<i>x</i>

Zeolitic Imidazolate Framework Coated ZnO Nanorods as Molecular Sieving to Improve Selectivity of Formaldehyde Gas Sensor

Zinc oxide (ZnO) and zeolitic imidazolate framework-8 (ZIF–8) core–shell heterostructures were obtained by using the self-template strategy where ZnO nanorods not only act as the template, but also provide Zn²⁺ ions for the formation of ZIF–8 shell. The ZIF–8 shell was uniformly deposited to form ZnO@ZIF–8 nanorods with core–shell heterostructures at 70 °C for 24 h as the optimum reaction time by the hydrothermal synthesis. Transmission electron microscopy (TEM) images revealed that the ZnO@ZIF–8 heterostructures are composed of ZnO as core and ZIF–8 as shell. Nitrogen (N₂) sorption isotherms demonstrated that the as-prepared ZnO@ZIF–8 nanorods are a typical microporous material. Additionally, the ZnO@ZIF–8 nanorods sensor exhibited distinct gas response for reducing gases with different molecule sizes. The selectivity of the ZnO@ZIF–8 nanorods sensor was obviously improved for the detection of formaldehyde owing to the limitation effect of the aperture of ZIF–8 shell. This study demonstrated that semiconductor@MOF core–shell heterostructures may be a novel way to enhance the selectivity of the gas sensing materials

Ordered and Ultralong Graphitic Carbon Nitride Nanotubes Obtained via In-Air CVD for Enhanced Photocatalytic Hydrogen Evolution

Metal-free graphitic carbon nitride (g-C3N4) has become one of the most up-and-coming photocatalyst candidates for the hydrogen evolution reaction. However, the improvement in photocatalytic property is strongly suppressed by the limited active reaction sites due to the bulk microstructure of g-C3N4. On this basis, we exploit a moderate and economical approach to prepare an ordered and one-dimensionally ultralong carbon nitride nanotube (CN-NT) via the in-air chemical vapor deposition (CVD) with SiO2 nanofiber templates synthesized by electrostatic spinning. Due to the uniform size, fluffiness, and easy removal, SiO2 nanofiber templates are conducive to prepare ordered and tubular CN-NT. The obtained CN-NT sample exhibits an excellent photocatalytic hydrogen evolution rate (HER) of 4605.2 μmol·h–1·g–1 under visible light, which is 33.4 times higher than that of the original bulk g-C3N4. The apparent quantum efficiency reaches 6.49% at 420 nm. The enhancement in the photocatalytic activity is ascribed to the increased specific surface area, faster electron transfer pathway, advanced light absorption ability, and furthermore the lower recombination rate of photogenerated electrons

Flexible Lead-Free BiFeO₃/PDMS-Based Nanogenerator as Piezoelectric Energy Harvester

Perovskite ferroelectric BiFeO₃ has been extensively researched in many application fields, but has rarely been investigated for the energy conversion of tiny mechanical motions in electricity in spite of its large theoretical remnant polarization. Here we demonstrate the fabrication of a flexible piezoelectric nanogenerator based on BiFeO₃ nanoparticles (NPs), which were synthesized using a sol–gel process. The BiFeO₃ NPs–PDMS composite device exhibits an output open circuit voltage of ∼3 V and short circuit current of ∼250 nA under repeated hand pressing. The output generation mechanism from the PNG is discussed on the basis of the alignment of electric dipoles in the composite film. It is demonstrated that the output power from the PNG can directly drive the light-emitting diode (LED) and charge capacitor. These results demonstrate that BiFeO₃ nanomaterials have the potential for large-scale lead-free piezoelectric nanogenerator applications

Electro-mechano-optical properties of the Er³⁺ modified Bi_0.5Na_0.4K_0.1TiO₃ versatile ceramics

A series of Bi Er Na K TiO (BNKT-xEr) ceramics were designed and fabricated, the dopant effects on dielectric, piezoelectric and photoluminescence properties were studied. The results show that the piezoelectric property of BNKT can be enhanced by a trace amount of Er dopant, which is also reflected in the large linear electrostrain (S = 0.29%, under 55 kV/cm) achieved in BNKT-0.0025 Er. On the other hand, higher Er content can produce excellent dielectric temperature stability, with △ԑ/ԑ < ±15% over temperature range of 90∼510 °C. Meanwhile, all BNKT-xEr ceramics exhibit good photoluminescence properties, which may open new applications of these multifunctional ceramics. 0.5- x x 0.4 0.1 3 uni 150 °

Cyanuric Acid-Assisted Synthesis of Hierarchical Amorphous Carbon Nitride Assembled by Ultrathin Oxygen-Doped Nanosheets for Excellent Photocatalytic Hydrogen Generation

Amorphous carbon nitride with typical short-range order arrangement as an effective photocatalyst is worth exploring but remains a great challenge because its disordered structure induces severe recombination of photogenerated charge carriers. Herein, for the first time, we demonstrate that a hierarchical amorphous carbon nitride (HACN) with structural oxygen incorporation can be synthesized via a cyanuric acid-assisted melem hydrothermal process, accompanied by freeze-drying and pyrolysis. The complex composed of melem and cyanuric acid exhibiting a unique 3D self-supporting skeleton and significant phase transformation is responsible for the formation of an interconnected hierarchical framework and amorphous structure for HACN. These features are beneficial to enhance its visible light harvesting by the multiple-reflection effect within the architecture consisting of more exposed porous nanosheets and introducing a long band tail absorption. The well-designed morphology, band tail state, and oxygen doping effectively inhibit rapid band-to-band recombination of the photogenerated electrons and holes and facilitate subsequent separation. Accordingly, the HACN catalyst exhibits exceptional visible light (λ > 420 nm)-driven photoreduction for hydrogen production with a rate of 82.4 μmol h–1, which is 21.7 and 9.5 times higher than those of melem-derived carbon nitride and crystalline nanotube carbon nitride counterparts, respectively, and significantly surpasses those of most reported amorphous carbon nitrides. Our controlling of rearrangement of the in situ supramolecular self-assembly of melem oligomer using cyanuric acid directly instructs the development of highly efficient amorphous photocatalysts for converting solar energy into hydrogen fuel

Large electrostrain in Bi_1/2Na_1/2TiO₃-based relaxor ferroelectrics: A case study of Bi_1/2Na_1/2TiO₃-Bi_1/2K_1/2TiO₃-Bi(Ni_2/3Nb_1/3)O₃ ceramics

(1-x)(0.8Bi Na TiO -0.2Bi K TiO )-xBi(Ni Nb )O (BNKT-xBNN) solid solution ceramics were fabricated by high temperature solid-state reaction method. All the compositions possess relaxor ferroelectric features, among which the ergodic BNKT-0.02BNN exhibits large repeatable electrostrain value S = 0.51% at electric field of 65 kV/cm, with high piezoelectric stain coefficient d ∗ of 890 pm/V at 45 kV/cm, while the non-ergodic compositions present unrepeatable large strain response. Based on the electric field-composition phase diagram, the repeatability of strain response in ergodic compositions can be attributed to the reversible electric-field-induced phase transition. In addition, the effects of BNN contents on the macroscopic strain properties are explored by analyzing the existing states of the polar regions with corresponding thermal evolutions and electric-field-induced phase transitions. This research is expected to guide the design of lead free relaxor ferroelectric materials with desired electrostrain properties. 1/2 1/2 3 1/2 1/2 3 2/3 1/3 3 uni 3

Triboelectric Nanogenerators Based on Fluorinated Wasted Rubber Powder for Self-Powering Application

We report a new high output triboelectric nanogenerator (TENG) based on the contact-separation mode using surface fluorinated wasted rubber powder (WRP) as a source material. The WRP-TENG’s configuration is designed by serving WRP as negatively charged friction electrode and water assisted oxidized (WAO) Al film as positively charged friction electrode. The open-circuit voltage (<i>V</i>_oc) and short-circuit current density (<i>J</i>_sc) of the WRP based TENGs increase with decrease in the particle size of WRP. More importantly, after surface fluorination of WRP with modifier of trichloro (1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorooctyl) silane (FOTS), the maximum <i>V</i>_oc and <i>J</i>_sc of the WRP based TENG is further increased to 265 V and 75 mA/m², respectively. The FWRP based TENG can drive 100 commercial LEDs directly. In addition, a self-powered hygrothermograph is designed, showing great potential application in daily life. The advantages such as simple fabrication process, low cost, and stability of this TENG make it a promising design for an energy harvesting device or for self-powered electronics. Furthermore, it presents a significant opportunity for the extension of waste utilization