Environment‐friendly lead‐free piezoelectric ceramics have been studied extensively in the past decade with great progress particularly in systems based on a niobate perovskite compound formulated as ...(K, Na)NbO3 (abbreviated as KNN). A comprehensive review on the latest development of KNN‐based piezoelectric ceramics is presented in this article, including the phase structure, property enhancement approaches, and sintering processes as well as the status of some promising applications. The phase structure of KNN was reexamined and associated with the effect of chemical modification on its tetragonal‐to‐orthorhombic transition. Then, a special focus is placed on the temperature dependence of piezoelectric properties of KNN‐based ceramics, followed by reviewing the recent approaches devoted to the temperature‐stability enhancement. The processing fundamentals related to the sintering of KNN‐based ceramics are also presented with an emphasis on compositional and microstructural control. Finally, this review introduces several industrial attempts of traditional piezoceramic products using KNN‐based ceramics and the studies on some promising application in authors' laboratory.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
The demand for high-temperature dielectric materials arises from numerous emerging applications such as electric vehicles, wind generators, solar converters, aerospace power conditioning, and ...downhole oil and gas explorations, in which the power systems and electronic devices have to operate at elevated temperatures. This article presents an overview of recent progress in the field of nanostructured dielectric materials targeted for high-temperature capacitive energy storage applications. Polymers, polymer nanocomposites, and bulk ceramics and thin films are the focus of the materials reviewed. Both commercial products and the latest research results are covered. While general design considerations are briefly discussed, emphasis is placed on material specifications oriented toward the intended high-temperature applications, such as dielectric properties, temperature stability, energy density, and charge-discharge efficiency. The advantages and shortcomings of the existing dielectric materials are identified. Challenges along with future research opportunities are highlighted at the end of this review.
The development of lead‐free piezoceramics has attracted great interest because of growing environmental concerns. A polymorphic phase transition (PPT) has been utilized in the past to tailor ...piezoelectric properties in lead‐free (K,Na)NbO3 (KNN)‐based materials accepting the drawback of large temperature sensitivity. Here a material concept is reported, which yields an average piezoelectric coefficientd33 of about 300 pC/N and a high level of unipolar strain up to 0.16% at room temperature. Most intriguingly, field‐induced strain varies less than 10% from room temperature to 175 °C. The temperature insensitivity of field‐induced strain is rationalized using an electrostrictive coupling to polarization amplitude while the temperature‐dependent piezoelectric coefficient is discussed using localized piezoresponse probed by piezoforce microscopy. This discovery opens a new development window for temperature‐insensitive piezoelectric actuators despite the presence of a polymorphic phase transition around room temperature.
The development of (K,Na)NbO3‐based lead‐free piezoceramics is attracting great interest because of growing environmental concerns. A material concept that yields an average piezoelectric coefficient, d33, of about 300 pC/N and a high level of unipolar strain up to 0.16% is reported. Most intriguingly, field‐induced strain varies less than 10% from room temperature to 175 °C.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
High piezoelectricity of (K,Na)NbO3 (KNN) lead‐free materials benefits from a polymorphic phase transition (PPT) around room temperature, but its temperature sensitivity has been a bottleneck ...impeding their applications. It is found that good thermal stability can be achieved in CaZrO3‐modified KNN lead‐free piezoceramics, in which the normalized strain d
33* almost keeps constant from room temperature up to 140 °C. In situ synchrotron X‐ray diffraction experiments combined with permitivity measurements disclose the occurrence of a new phase transformation under an electrical field, which extends the transition range between tetragonal and orthorhombic phases. It is revealed that such an electrically enhanced diffused PPT contributed to the boosted thermal stability of KNN‐based lead‐free piezoceramics with high piezoelectricity. The present approach based on phase engineering should also be effective in endowing other lead‐free piezoelectrics with high piezoelectricity and good temperature stability.
A material concept of electrically enhanced diffused polymorphic phase transition (EED‐PPT) is developed to resolve the long‐standing issue of temperature‐sensitivity in lead‐free (K,Na)NbO3 piezoelectrics. Experimental and theoretical studies reveal that EED‐PPT can remarkbaly boost the temperature stability of (K,Na)NbO3, where the normalized strain d33* almost keeps constant from room temperature up to 140 °C.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Large single crystals serve as an ideal platform for investigating intrinsic material properties and optoelectronic applications. Here we develop a method, namely, room-temperature liquid diffused ...separation induced crystallization that uses silicone oil to separate the solvent from the perovskite precursors, to grow high-quality perovskite single crystals. The growth kinetics of perovskite single crystals using this method is elucidated, and their structural and optoelectronic properties are carefully characterized. The resultant perovskite single crystals, taking CH
NH
PbBr
as an example, exhibit approximately 1 µs lifetime, a low trap density of 4.4 × 10
cm
, and high yield of 92%, which are appealing for visible light or X-ray detection. We hope our findings will be of great significance for the continued advancement of high-quality perovskite single crystals, through a better understanding of growth mechanisms and their deployment in various optoelectronics. The diffused separation induced crystallization strategy presents a major step forward for advancing the field on perovskite single crystals.
Structural health monitoring technology can assess the status and integrity of structures in real time by advanced sensors, evaluate the remaining life of structure, and make the maintenance ...decisions on the structures. Piezoelectric materials, which can yield electrical output in response to mechanical strain/stress, are at the heart of structural health monitoring. Here, we present an overview of the recent progress in piezoelectric materials and sensors for structural health monitoring. The article commences with a brief introduction of the fundamental physical science of piezoelectric effect. Emphases are placed on the piezoelectric materials engineered by various strategies and the applications of piezoelectric sensors for structural health monitoring. Finally, challenges along with opportunities for future research and development of high-performance piezoelectric materials and sensors for structural health monitoring are highlighted.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A simple achievement of six different super-wettabilities on the femtosecond laser ablated polydimethylsiloxane (PDMS) surface is reported for the first time. Both the experimental and theoretical ...analysis revealed that underwater oil wettability and underwater bubbles' behavior on a solid surface are closely related to the in-air water wettability of the substrate surface. The original femtosecond laser-induced microstructured PDMS surface exhibited excellent superhydrophobicity in air and generally became superoleophilic and superaerophilic in water. After being further irradiated by oxygen plasma, the rough PDMS surface switched to superhydrophilic. Underwater superoleophobicity and superaerophobicity could be exhibited when such a superhydrophilic PDMS surface was immersed in water. Furthermore, various superhydrophobic–superhydrophilic, underwater superoleophobic–superoleophilic and underwater superaerophobic–superaerophilic hybrid patterns were successfully designed and achieved on the femtosecond laser ablated PDMS surface by subsequent selective oxygen plasma treatment. We believe that the reported preparation principle of superhydrophobic, superhydrophilic, underwater superoleophobic, underwater superoleophilic, underwater superaerophobic, and underwater superaerophilic surfaces would have important guiding significance to researchers and engineers to effectively control water droplets, oil droplets and the behavior of bubbles on a material surface.
Osteosarcoma (OS) is a lethal malignancy of the bone, jeopardizing the life of an enormous population worldwide. There are grand ongoing challenges to improve overall patient survival. Herein, a ...synergetic chemo‐piezodynamic therapy by defect‐engineered lead‐free piezoelectric (K,Na)NbO3 (KNN) is reported, which can generate reactive oxygen species (ROS) to effectively circumvent OS. Significant anti‐tumor effects in human OS cells, and xenograft OS models are observed that almost stop the growth of the tumors after treatment with KNN because of oxygen vacancies‐driven free radical catalysis (namely, the chemodynamic therapy), and those effects are enhanced after introducing ultrasonic vibration enabled by the ultrasound‐triggered piezocatalysis (piezodynamic therapy). Moreover, it is found that KNN induces apoptosis and autophagy of OS cells and shows good histocompatibility on evaluation in mouse models, which has no killing effect on normal cells and no toxic effects on organs in vivo. Both in vitro cellular level evaluation and in vivo OS xenograft assessment have demonstrated that injectable KNN nanocrystals induce cytotoxicity and tumor eradication by the synergy of chemo‐piezocatalytic effects. This study opens an avenue for customized design of high‐tech nanocatalysts by integrating synergetic catalytic effects for therapeutic applications in tumor healthcare.
Defect‐engineered piezoelectric nanocrystals integrated with ultrasonic therapy modality are demonstrated as a low poison effect and highly efficient antitumor reagent for osteosarcoma treatment. This new strategy combines chemocatalytic and piezocatalytic effects to yield massive reactive oxygen species in treating tumors both in primary tumor and lung metastases to address the main issue of toxicity and side effects of conventional antitumor drug therapy.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The development of lead-free ceramics for electrostatic energy storage has attracted great interest because of the growing environmental concerns. Despite the extensive exploration, the unsuccess in ...synergistically optimizing both energy density and efficiency of polycrystalline materials is the major hurdle for their practical applications. Herein, Bi(Mg0.5Zr0.5)O3-modified BaTiO3 lead-free relaxor ferroelectric ceramics are demonstrated to be viable candidates for energy storage. The materials can simultaneously deliver a high recoverable energy density of 2.9 J cm−3 and a high energy efficiency of 86.8%, which are enhanced by 625% and 156% over those of unmodified BaTiO3, while keeping insensitive to thermal stimulus over 30–150 °C. It is unveiled that the incorporation of Bi(Mg0.5Zr0.5)O3 favors the formation of polar nanoregions (PNRs), as evidenced by transmission electron microscope and piezoresponse force microscopy, which increases the threshold field to induce long range order and decreases the stability thereof, contributing to the more linear-towards polarization behavior. The dynamic PNRs along with the decreased grain size, increased bulk density, and consequently enhanced dielectric breakdown strength (301.4 kV cm−1) are responsible for the superior energy storage performance of Bi(Mg0.5Zr0.5)O3-modified BaTiO3 ceramics. This work opens up a new avenue to tailor lead-free dielectrics toward high energy storage performance for electrical energy storage.
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•BT-BMZ relaxors with excellent comprehensive energy storage performance have been achieved by domain engineering.•The obtained excellent thermal stability of energy storage performance is of great importance for practical applications.•The dynamics of nanodomains is studied to reveal the underlying mechanism of energy storage performance of relaxors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The carrier concentration of the electron‐selective layer (ESL) and hole‐selective layer can significantly affect the performance of organic–inorganic lead halide perovskite solar cells (PSCs). ...Herein, a facile yet effective two‐step method, i.e., room‐temperature colloidal synthesis and low‐temperature removal of additive (thiourea), to control the carrier concentration of SnO2 quantum dot (QD) ESLs to achieve high‐performance PSCs is developed. By optimizing the electron density of SnO2 QD ESLs, a champion stabilized power output of 20.32% for the planar PSCs using triple cation perovskite absorber and 19.73% for those using CH3NH3PbI3 absorber is achieved. The superior uniformity of low‐temperature processed SnO2 QD ESLs also enables the fabrication of ≈19% efficiency PSCs with an aperture area of 1.0 cm2 and 16.97% efficiency flexible device. The results demonstrate the promise of carrier‐concentration‐controlled SnO2 QD ESLs for fabricating stable, efficient, reproducible, large‐scale, and flexible planar PSCs.
SnO2 quantum dots (QDs) are synthesized by a simple and reproducible two‐step low‐temperature method, in which the carrier concentration of colloidal SnO2 QDs is controlled. Planar perovskite solar cells with efficiencies of 20.8% in small size (0.09 cm2), ≈19% in large size (1 cm2), and 16.97% for flexible devices with low‐temperature processed SnO2 QD electron‐selective layers are obtained.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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