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.
The culture of Zen comes into two diverse paths in China and Japan. Compared to China, the Japanese Zen culture has characteristics of natural, plain, sensitive, vanity and silence. It is ...unrestrained with feeble and desolation. And these characteristics are presented in Japanese domestic ceramic in the unique beauty of its domestic ceramic.
•High-entropy boride-carbide two-phase ultrahigh temperature ceramics are made.•This work further extends the emerging field of high-entropy ceramics.•A novel reactive spark plasma sintering route ...produces > ∼99 % dense specimens.•A thermodynamic relation governing the equilibrium phase compositions is discovered.•The hardness is higher than the weighted average of the two high-entropy phases.
A series of dual-phase high-entropy ultra-high temperature ceramics (DPHE-UHTCs) are fabricated starting from N binary borides and (5-N) binary carbides powders. > ∼99 % relative densities have been achieved with virtually no native oxides. These DPHE-UHTCs consist of a hexagonal high-entropy boride (HEB) phase and a cubic high-entropy carbide (HEC) phase. A thermodynamic relation that governs the compositions of the HEB and HEC phases in equilibrium is discovered and a thermodynamic model is proposed. These DPHE-UHTCs exhibit tunable grain size, Vickers microhardness, Young’s and shear moduli, and thermal conductivity. The DPHE-UHTCs have higher hardness than the weighted linear average of the two single-phase HEB and HEC, which are already harder than the rule-of-mixture averages of individual binary borides and carbides. This study extends the state of the art by introducing dual-phase high-entropy ceramics (DPHECs), which provide a new platform to tailor various properties via changing the phase fraction and microstructure.
This book describes advances in the development of smart and new ceramic materials for different applications. It also describes recent and expected challenges, along with their potential solutions, ...in advanced methods for the fabrication and characterization of nano-ceramics and their composites. This book provides readers with a comprehensive and updated review of the latest research in the field.
We present a novel processing route to synthesize homogeneous ceramic polymer composites with ultrahigh (a1478 vol.%) packing density by using the spouted bed granulation technology and subsequent ...warm pressing. In the granulation process, two ceramic particle size fractions (I--Al2O3) and a thermoplastic polymer (polyvinyl butyral) are assembled to granules. In the process, mu m-sized particles are coated with a layer of polymer which contains a second, nm-sized ceramic particles fraction. The mass fractions of each constituents can be adjusted independently. During the warm pressing, the nm-sized particle fraction along with polymer is pressed into the void volume of the mu m-sized particles, thus achieving a homogeneous, isotropic composite structure with a very high packing density of ceramic particles. The material, which can easily be produced in large quantities, combines a high modulus of elasticity (up to 69 GPa), tensile strength (a1450 MPa), and pronounced fracture strain (a140.1%) with an isotropic, biocompatible, metal-free composition. Possible failure mechanisms are discussed, including failure due to necking of the polymer, and failure due to limited polymeraparticle-interfacial strength.
The study on novel physical properties of structural ceramics or ceramic composites could make them more conducive to be function‐ and structure‐integrated materials. Herein, titanium nitride‐alumina ...(TiN–Al2O3) duplex ceramics were prepared and the dielectric spectra of the ceramics were studied from 10 MHz to 1 GHz. Negative permittivity appeared when TiN content exceeded 40 wt% due to the induced plasmonic state of massive delocalized electrons in connected TiN grain networks. Meanwhile, alternating current conduction behaviors of the duplex ceramics were discussed with percolation theory. Furthermore, the analysis of reactance by equivalent circuit models indicated that negative permittivity ceramics exhibited inductive character. This work realized negative dielectric behaviors in TiN–Al2O3 duplex ceramics and would promote the study of electromagnetic functionalization in wave shielding or attenuation for structural ceramics.
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