Highly transparent lead‐free (1‐x)K0.5Na0.5NbO3–xSr(Zn1/3Nb2/3)O3 (KNN–xSZN) ferroelectric ceramics have been synthesized via a conventional pressureless sintering method. All samples are optically ...clear, showing high transmittance in the visible and near‐infrared regions (~70% and ~80% at 0.5 mm of thickness, respectively). This exceptionally good transmittance is due to the pseudo‐cubic phase structure as well as the dense and fine‐grained microstructure. In addition, a high energy storage density of 3.0 J/cm3 has been achieved for the 0.94K0.5Na0.5NbO3–0.06Sr(Zn1/3Nb2/3)O3 ceramics with submicron‐sized grains (~136 nm). The main reason is likely to be the typical relaxor‐like behavior characterized by diffuse phase transition, in addition to the dense and fine‐grained microstructure. This study demonstrates that the 0.94K0.5Na0.5NbO3–0.06Sr(Zn1/3Nb2/3)O3 ceramic is a promising candidate of lead‐free transparent ferroelectric ceramics for new areas beyond transparent electronic device applications.
Texturing is an effective approach to improving the piezoelectricity of piezoelectric ceramics. In this work, textured Li+‐doped 0.852Bi0.5Na0.5TiO3–0.11Bi0.5K0.5TiO3–0.038BaTiO3 ternary lead‐free ...piezoelectric ceramics are prepared by the reactive templates grain growth (RTGG) method. X‐ray diffraction (XRD) results demonstrate a high orientation degree of 77% along the direction. Outstanding electro‐strain response, which is higher than most of reported BNT‐based textured ceramics, is achieved due to the contribution of oriented‐grains along the direction. A large electro‐strain of 0.55% with a relatively low hysteresis is obtained at 6.5 kV/mm with corresponding large signal piezoelectric coefficient (d33∗) of 846 pm/V in the textured ceramics, which is 49% higher than that of the random ceramics. Besides, the electro‐strain could reach as high as 0.52%@5.5 kV/mm (d33∗ = 945 pm/V) at 100°C. These results indicate that the RTGG is an effective way to design high performance lead‐free piezoelectric materials.
In the original publication of this article, the title was printed as “Four Preceramic Points Newly Discovered in Belize: A Comment on Stemp et al. (1996:279–299).” The article has been updated to ...the correct title. The authors apologize for this error.
Carbon–carbon (C–C) composites are attractive materials for hypersonic flight vehicles but they oxidize in air at temperatures >500°C and need thermal protection systems to survive aerothermal ...heating. We investigated using multilayers of high‐temperature ceramics such as ZrB2 and SiC to protect C–C against oxidation. Our approach combines pretreatment and processing steps to create continuous and adherent high‐temperature ceramic coatings from infiltrated preceramic polymers. We tested our protective coatings at temperatures above 2600°C at the National Solar Thermal Testing Facility using controlled cold‐wall heat flux profiles reaching a maximum of 680 W/cm2.
The ability to pattern ceramic materials in three dimensions (3D) is critical for structural, functional, and biomedical applications. One facile approach is direct ink writing (DIW), in which 3D ...structures are built layer‐by‐layer through the deposition of colloidal‐ or polymer‐based inks. This approach allows one to design and rapidly fabricate ceramic materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. In this feature article, we present both droplet‐ and filament‐based DIW techniques. We focus on the various ink designs and their corresponding rheological behavior, ink deposition mechanics, potential shapes and the toolpaths required, and representative examples of 3D ceramic structures assembled by each technique. The opportunities and challenges associated with DIW are also highlighted.
High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements. Although in the infant ...stage, the emerging of this new family of materials has brought new opportunities for material design and property tailoring. Distinct from metals, the diversity in crystal structure and electronic structure of ceramics provides huge space for properties tuning through band structure engineering and phonon engineering. Aside from strengthening, hardening, and low thermal conductivity that have already been found in high-entropy alloys, new properties like colossal dielectric constant, super ionic conductivity, severe anisotropic thermal expansion coefficient, strong electromagnetic wave absorption, etc., have been discovered in HECs. As a response to the rapid development in this nascent field, this article gives a comprehensive review on the structure features, theoretical methods for stability and property prediction, processing routes, novel properties, and prospective applications of HECs. The challenges on processing, characterization, and property predictions are also emphasized. Finally, future directions for new material exploration, novel processing, fundamental understanding, in-depth characterization, and database assessments are given.
Issue Title: Special Issue on Advances in Piezoelectrics: Fundamentals, Characterization, Materials and Applications, Guest Editor: Dragan Damjanovic Investigations in the development of lead-free ...piezoelectric ceramics have recently claimed comparable properties to the lead-based ferroelectric perovskites, represented by Pb(Zr,Ti)O^sub 3^, or PZT. In this work, the scientific and technical impact of these materials is contrasted with the various families of "soft" and "hard" PZTs. On the scientific front, the intrinsic nature of the dielectric and piezoelectric properties are presented in relation to their respective Curie temperatures (T ^sub C^) and the existence of a morphotropic phase boundary (MPB). Analogous to PZT, enhanced properties are noted for MPB compositions in the (Na,Bi)TiO^sub 3^-BaTiO^sub 3^ and ternary system with (K,Bi)TiO^sub 3^, but offer properties significantly lower. The consequences of a ferroelectric to antiferroelectric transition well below T ^sub C^ further limits their usefulness. Though comparable with respect to T ^sub C^, the high levels of piezoelectricity reported in the (K,Na)NbO^sub 3^ family are the result of enhanced polarizability associated with the orthorhombic-tetragonal polymorphic phase transition being compositionally shifted downward. As expected, the properties are strongly temperature dependent, while degradation occurs through the thermal cycling between the two distinct ferroelectric domain states. Extrinsic contributions arising from domains and domain wall mobility were determined using high field strain and polarization measurements. The concept of "soft" and "hard" lead-free piezoelectrics were discussed in relation to donor and acceptor modified PZTs, respectively. Technologically, the lead-free materials are discussed in relation to general applications, including sensors, actuators and ultrasound transducers.PUBLICATION ABSTRACT
BiFeO3–BaTiO3 (BF-BT)-based lead-free ferroelectric ceramic has attracted immense interest in energy storage applications due to its great spontaneous polarization (Pmax) strength. However, high ...remanent polarization (Pr) has become a serious obstruction for its practical application. In this work, Sm ions were doped into 0.67BiFeO3-0.33BaTiO3 (0.67Bi1-xSmxFeO3-0.33BaTiO3, BSxF-BT) to tailor the structure and energy storage properties. It was found that the doping of Sm ions effectively reduced Pr by enhancing the relaxor behavior of BF-BT ceramic, which produce an enhancement in the energy storage performance. Large recoverable energy storage density Wrec of 2.8 J/cm3 with moderate energy storage efficiency η of 55.8% (200 kV/cm) were achieved in the ceramics with x = 0.1. Moreover, the energy storage capabilities exhibited good stability at temperature (20–95 °C) and frequency (0.1–50 Hz). Furthermore, the ceramic also possessed a predominant discharge speed with a discharge time less than 0.1 μs in a circuit with a load of 200 Ω. These results showed that the Wrec and η of BF-BT ceramic could be availably promoted by the doping of Sm ions, which may be helpful for the enhancement of energy storage performance of BF-BT-based ceramics.
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