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Freeze casting of aqueous suspension was investigated as a method for fabricating hydroxyapatite (HA) porous ceramics with lamellar structures. The rheological properties of HA suspensions employed in the ice-templated process were investigated systematically. Well aligned lamellar pores and dense ceramic walls were obtained successfully in HA porous ceramics with the porosity of 68-81% and compressive strength of 0.9-2.4 MPa. The results exhibited a strong correlation between the rheological properties of the employed suspensions and the morphology and mechanical properties of ice-templated porous HA ceramics, in terms of lamellar pore characteristics, porosities and compressive strengths. The ability to produce aligned pores and achieve the manipulation of porous HA microstructures by controlling the rheological parameters were demonstrated, revealing the potential of the ice-templated method for the fabrication of HA scaffolds in biomedical applications., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Powder‐based piezo‐catalysis, as an effective approach to degrade wastewater and produce hydrogen from water splitting, has been widely used in the field of energy conservation and pollution reduction. However, these hard‐to‐recycle powders pose a challenge of secondary pollution in the environment. As a result, this paper provides an alternative strategy based on the manufacture of porous ceramics as a green chemistry approach to replace ferroelectric powders currently used in traditional piezo‐catalysis. The piezo‐catalytic properties of Ba0.75Sr0.25TiO3 (BST) ceramics prepared using freeze casting and direct ink writing techniques are investigated in detail. The positive effect of introducing micro‐ and macro‐pores is explored and discovered, where a BST ceramic with hierarchical pore channels is prepared by a combination of direct ink writing and freeze casting and exhibts the highest first‐order kinetic rate constant per mass of catalysts, k, of up to 2.91 min−1 kg−1 compared to bulk BST ceramics. This study therefore provides the first report for the benefits of hierarchical porous ferroelectric ceramics used in water splitting, with an average H2 production rate reaching 848.88 nmol g−1 h−1. [ABSTRACT FROM AUTHOR]

A series of barium zirconate modified potassium sodium niobate-based lead-free piezoelectric ceramics [(0.97-x)(K0.45Na0.55)(Nb0.97Sb0.03)O3-0.03Bi0.5K0.075Na0.425ZrO3-xBaZrO3, KNNS–BKNZ–xBZ, x = 0 ~ 0.02] were prepared by the traditional solid-state method. The effect of BZ on the phase structure and electrical properties was systematically studied. Rhombohedral–orthorhombic–tetragonal multiphase coexistence structure can be observed for the whole ceramic system while the addition of BZ leads to the reduction in the orthorhombic phase content and increase in the rhombohedral and tetragonal phase content. At the critical composition with x = 0.01, the ceramics show the optimized electrical properties with the piezoelectric constant d33 of 265 pC/N, unipolar strain Suni of 0.168%, inverse piezoelectric coefficient d33* of 480 pm/V, room-temperature dielectric constant εr of 1634, and Curie temperature TC of 282 °C. Moreover, enhanced temperature stability was achieved in the x = 0.01 ceramics, presenting the variation of d33 less than 15% within the temperature range of 20–100 °C and the Suni remained above 80% until the elevated temperature of 175 °C. [ABSTRACT FROM AUTHOR]

In this work, (1 − x)(0.94Na0.5Bi0.5TiO3–0.06BaTiO3)–xKTaO3 (x = 0–0.30) ceramics are developed for dielectric capacitor applications. The introduction of KTaO3 from x = 0 to 0.30 increases the tolerance factor t from 0.984 to 1.005 and causes the decrease of ferroelectric rhombohedral phase in the ceramics. Besides, a gradual structural change toward a higher symmetry can be detected, accompanied by the obvious domain refinement. In the aspect of electrical property, the strengthened dielectric relaxation leads to the greatly enhanced thermal stability of dielectric response. The decline in Ts from 98 to −96°C causes a significant widening of the low‐temperature region with temperature‐stable dielectric constant εr and low dielectric loss tan δ. The x = 0.30 ceramic shows a high εr (25°C) of 1094 with the temperature coefficient of capacitance ≤±15% over −70 to 200°C, which exceeds the X9R standard. Meanwhile, tan δ is less than 0.02 in a wide temperature range of −35 to 300°C. In addition, the ultrafine grain size of 290 nm, large bandgap of 3.22 eV, and high resistance of the x = 0.30 ceramic contribute to its electrical breakdown strength. A linear‐like P–E loop with the large discharged energy density WD ∼ 3.50 J/cm3 and high energy efficiency η ∼ 90.1% is obtained under 28 kV/mm at room temperature. The thermal stability of the energy storage performance is also satisfactory with the variation of WD less than 15% over −40 to 200°C, and the η is higher than 85%. [ABSTRACT FROM AUTHOR]

Due to the unique electromechanical energy conversion capability of ferroelectric materials, they have been at the forefront of materials science for a variety of applications such as sensors, actuators and energy harvesting. Researchers have focused on exploring approaches to achieve improved ferroelectric performance, and to ensure that the available material systems are more environmentally friendly. This comprehensive review summarizes recent research progress on porous ceramics and highlights the variety of factors that are often ignored, namely the influence of porosity on the Curie temperature, and applications of porous ferroelectric materials with adjustable Curie temperature. Finally, the development trends and challenges of porous ferroelectric materials are discussed, aiming to provide new insights for the design and construction of ferroelectric materials. [ABSTRACT FROM AUTHOR]

The apparent incompatibility between d33 and Qm in potassium sodium niobate-based lead-free ceramics is an obstacle to their applications. In this study, (K0.5Na0.5)0.98Li0.02Nb0.82Ta0.18O3 (LT-KNN) system near the orthorhombic–tetragonal (O–T) phase boundary but in the O phase region is selected as the matrix to ensure a relatively large d33 and high Tc, and help the CuO doping generate an effective "hardening" effect to improve Qm. The results show that adding proper amount of CuO into LT-KNN promotes the densification of ceramics and suppresses the abnormal grain growth, which helps to decrease the dielectric loss and obtain a high poling efficiency. Moreover, the Cu2+ doping in B-site (Nb/Ta)5+ generates oxygen vacancies ( V O ∙ ∙ ) and the Cu Nb / Ta ″ ′ - V O ∙ ∙ ′ defect dipoles could be formed, resulting an obvious "hardening" effect. With the introduction of 1 mol% CuO, the d33 increases from 82 to 180 pC/N and the Qm presents an abrupt rise from 136 to 665. More intriguingly, the addition of CuO delays the O–T phase transition while maintaining a high Tc of ~ 310 °C. Combined with the pinning effect of internal bias field, the d33 of 1 mol% CuO doped LT-KNN ceramics shows favorable stability in the wide temperature range of 20–280 °C, and a high Qm of larger than 250 can be achieved until 100 °C. Such a superior comprehensive electromechanical performance makes the ceramics promising in applications of high-power and high-frequency devices. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics featuring high piezoelectricity and fatigue resistance are extremely important in practical applications. In this work, 0.85Bi0.5Na0.5TiO3–0.11Bi0.5K0.5−xRbxTiO3–0.04BaTiO3 (x = 0–0.20) ceramics are developed, and the effects of Rb content on the crystalline phase, domain structure, electric property, and fatigue resistance are investigated. XRD results show that all the ceramics exhibit the rhombohedral/tetragonal morphotropic phase boundary. The introduction of Rb at A-sites induces enhanced relaxor characteristics. Increasing the Rb content leads to apparently decreased size and increased dynamics of ferroelectric domains, as revealed by the PFM and TEM observations. Notably, the fatigue resistance of ceramics is greatly improved with the introduction of Rb. In particular, the composition of x = 0.10 exhibits almost fatigue-free behaviors in conjunction with high piezoelectricity of d33 ~ 203 pC/N, which can be attributed to the formation of tweed-like nanodomains with a size of 10–20 nm and stripe-like nanodomains with an average width of ~ 3.5 nm. [ABSTRACT FROM AUTHOR]

Abstract: Polymer‐based capacitors with high energy density have attracted significant attention in recent years due to their wide range of potential applications in electronic devices. However, the obtained high energy density is predominantly dependent on high applied electric field, e.g., 400–600 kV mm−1, which may bring more challenges relating to the failure probability. Here, a simple two‐step method for synthesizing titanium dioxide/lead zirconate titanate nanowire arrays is exploited and a demonstration of their ability to achieve high discharge energy density capacitors for low operating voltage applications is provided. A high discharge energy density of 6.9 J cm−3 is achieved at low electric fields, i.e., 143 kV mm−1, which is attributed to the high relative permittivity of 218.9 at 1 kHz and high polarization of 23.35 µC cm−2 at this electric field. The discharge energy density obtained in this work is the highest known for a ceramic/polymer nanocomposite at such a low electric field. The novel nanowire arrays used in this work are applicable to a wide range of fields, such as energy harvesting, energy storage, and photocatalysis. [ABSTRACT FROM AUTHOR]

A novel percolative nanocomposite with super‐high permittivity and supressed dielectric loss is achieved, which is due to the hierarchical interfaces induced by BaSrTiO3 nanocuboid dotted graphene sheets and further modification of dapamine. [ABSTRACT FROM AUTHOR]

A novel ice/fiber-templated method was employed for the fabrication of hydroxyapatite scaffolds with the macro-channels of 250–350μm and lamellae spacings of 5–130μm. The macrochannels were formed by fibers, and the lamellae spacings were formed by ice crystals. As the final porosity of the ice/fiber-templated hydroxyapatite scaffolds increased from 56%to 73.6%, the corresponding compressive strengths decreased from 2.08 to 0.98 MPa. The results indicated that the microstructures and compressive strengths of the ice/fiber-templated hydroxyapatite scaffolds could be controlled by varying the solid loadings and packing densities of fibers. [ABSTRACT FROM AUTHOR]

A gelling system based on the polymerization of epoxy resin ethylene glycol diglycidyl ether ( EGDGE) and 3,3′-Diaminodipropylamine ( DPTA) was developed for gelcasting alumina ceramics. The gelation process of 50 vol% alumina-epoxy resin suspensions were investigated in accordance with the change in temperature and epoxy resin concentration. The activation energy Ea of polymerization reaction was 63.76 kJ/mol and no significant gelation was observed at 25°C during the test for 50 vol% Al2 O3 suspensions with 10 wt% EGDGE. With the increase in EGDGE concentration, Al2 O3 green bodies exhibited higher relative density, flexural strength, and Weibull modulus, reaching 64.4%, 41.03 MPa, and 12.51, respectively, when EGDGE concentration was 20 wt%. However, for sintered Al2 O3 bodies, the highest characteristic strength and Weibull modulus were obtained for 15 wt% EGDGE concentration, reaching 367.57 MPa and 14.52, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A novel route combining the conventional freeze casting and gel casting was proposed for the fabrication of aligned pore structures. In comparison with the conventional freeze casting, the utilization of a water-soluble Hydantoin epoxy resin in the freeze casting promoted the gelation process and led to a higher compressive strength of the green body. After sintering, the freeze gelcast samples exhibited a twice higher compressive strength and 15.6% higher porosity at the same time than those of conventional freeze cast sample. The improvements were attributed to the combination of gelation of Hydantoin epoxy resin and the aligned ice growth, which led to the coexistence of aligned cylindrical and lamellar pore structures. [Copyright &y& Elsevier]

Abstract: In this paper, a soft moulding method involving the use of elastomeric poly(dimethylsiloxane) (PDMS) moulds is described for micropatterning and microfabrication of ceramic components for microelectromechanical systems (MEMS) applications. The properties and microstructure of the green bodies have a direct effect on the ability to carry out some of the moulding procedures, as well as affecting the properties of the final sintered microcomponents. High packing density and mechanical strength are required for maintaining structural integrity and resisting the demoulding forces. Centrifuging force and appropriate binder systems have been introduced in the soft moulding process, and shown to be helpful in achieving uniform and dense green microcomponents with feature sizes of ≤100μm and high aspect ratio structures (<10). [Copyright &y& Elsevier]

This paper reports the preparation of highly concentrated aqueous alumina suspensions for demonstrating the microfabrication of ceramics by using soft molds of Poly(dimethyl siloxane) (PDMS) instead of the traditional solid molds. Zeta potential measurements showed very good dispersing effects of the dispersant NH4PAA. The rheological properties of concentrated aqueous alumina suspensions have been characterized with varying pH, NH4PAA concentration, solids loading and ultrasonic processing time. The intrinsic pH of the suspension was found suitable for molding. The optimum dispersant concentration is 0.14 wt.% and viscosities increase with more NH4PAA. A stable and easily processable suspension of 84.0 wt.% was achieved and suitable for soft-molding with viscosity of 0.30 Pa s at 100 s−1. Embossing and microtransfer molding have been used for soft-molding microfabrication and finally, crack-free and dense microstructures have been fabricated successfully with feature sizes of ∼30 μm. [Copyright &y& Elsevier]

Lead-free piezoelectric 0.8625NaNbO 3 -0.1BaTiO 3 -0.0375SrZrO 3 (0.8625NN-0.1BT-0.0375SZ) ceramics were prepared by templated grain growth method with NaNbO 3 templates. High orientation degree of 88.42% was achieved in the textured ceramics, which showed excellent piezoelectric performance with the quality factor Q m of 48.14 and the piezoelectric coefficient d 33 of 315 pC/N after poling. The grain morphology, crystal structure, P - E hysteresis loop, domain structures, frequency dependence of dielectric constant and loss tangent of conventional and textured 0.8625NN-0.1BT-0.0375SZ ceramics were systematically studied. It is indicated that ceramic texturing can effectively improve the piezoelectric performance of the NN-based lead-free piezoelectric ceramics, which provides a promising and broad prospect for the urgent development and practical applications of NN-based systems. • A highly oriented 0.8625NN-0.1BT-0.0375SZ textured ceramic is obtained. • The NN template excels in inducing grain growth of texture ceramics. • The dwelling time evidently affect the orientation of textured ceramics. • The texture process effectively improve the piezoelectric properties of ceramics. [ABSTRACT FROM AUTHOR]

In this work, lead-free (K 0.485 Na 0.485 Li 0.03)Nb 0.8 Ta 0.2 O 3 composition was designed to control the orthorhombic-tetragonal phases boundary near the room temperature as confirmed by Rietveld analysis, high-angle annular dark field scanning transmission electron microscopy, and temperature dependent dielectric constant. A comparative study of the direct and indirect synthesis methods was carried out and their functional properties were optimized as a function of sintering temperature (T s) and dwell time. Here, we achieved a large dynamic piezoelectric constant (d 33 *) of 510 pm/V under a very low electric field of 15–30 kV/cm. Moreover, an enhanced static piezoelectric constant (d 33) of 335 pC/N was obtained with a high Curie temperature (T C) of 315 °C. The large d 33 and d 33 * simultaneously with high T C in a single composition are promising results in lead-free polycrystalline ceramics. The strategic design of this work opens a new door for the possible development of novel functional materials for device applications. [ABSTRACT FROM AUTHOR]

As a promising lead-free high-temperature piezoelectric material, BiFeO 3 –BaTiO 3 (BF-BT) is still under debate on its crystal structure, especially for the compositions in the morphotropic phase boundary (MPB). Herein, the crystal structure of (1- x)BF- x BT ceramics near the MPB with x = 0.20–0.33 was analyzed by X-ray diffraction and Raman spectroscopy. With the addition of BT, the phase transition from distorted rhombohedral to pseudo-cubic structure was determined by Rietveld refinement. Raman analysis showed the weakening interactions between the A-site cations and BO 6 octahedron, as well as the degenerated distortions of BO 6 octahedron. Intriguingly, the results of X-ray photoelectron spectroscopy suggested the inhibition of Fe3+ reduction and decrease in oxygen vacancy concentration by the incorporation of BT. In terms of the electrical properties, the significant decline in Curie temperature, improvement in permittivity, and reduction in high-temperature dielectric loss can be observed with the increase of BT content. The increased remnant polarization, enhanced dielectric response and decreased coercive field were helpful for the piezoelectric performance. The maximum room-temperature piezoelectric coefficient of ∼160 pC/N and high-temperature piezoelectric coefficient of ∼324 pC/N were acquired in the x = 0.30 ceramics. This work provides a clear scope for further research on the structural transformation and high-temperature piezoelectric applications of BF-BT system. [ABSTRACT FROM AUTHOR]

• Propose a way to achieve high d 33 and T d simultaneously in BNT-based ceramics. • AlN introduction into BNT-BKT-BT greatly increases both d 33 from 165 to 234 pC/N and T d by ∼50 °C. • Stabilized tetragonal phase, high-density lamellar nanodomains, and increased grain size are obtained. The inverse relationship between piezoelectric coefficient (d 33) and depolarization temperature (T d) in Bi 0.5 Na 0.5 TiO 3 -based ceramics is a longstanding obstacle for their applications. In this work, synergistically enhanced d 33 and T d is achieved in AlN-modified 0.84Bi 0.5 Na 0.5 TiO 3 -0.11Bi 0.5 K 0.5 TiO 3 -0.05BaTiO 3 ceramics. Addition of 1 mol% AlN, increases both d 33 from 165 to 234 pC/N and T d by ∼50 °C. Rietveld analysis of X-ray powder diffraction (XRD) data reveals an increase in the proportion of the tetragonal phase at 1 mol% AlN incorporation. Moreover, at this composition the modified ceramics exhibit larger grains and high-density lamellar nanodomains with sizes of 30–50 nm. Polarization reversal and domain mobility are thus significantly enhanced, contributing to the large d 33. Temperature-dependent dielectric and XRD data revealed that the delayed thermal depolarization is attributed to the improved and poling-field stabilized tetragonality in the modified ceramics. [ABSTRACT FROM AUTHOR]

Porous hydroxyapatite (HA) ceramics with lamellar structures have been fabricated by an ice-templating process using as-synthesized and commercial HA powders. The viscosities of the suspensions prepared using the as-synthesized powders were 9–11times higher than those of the suspensions prepared using the commercial powders. Finer particle size resulted in larger lamellar pore width and a thinner porous ceramic wall, while a much denser ceramic wall, as well as lower porosity and higher compressive strength, was obtained with the commercial powder. [ABSTRACT FROM AUTHOR]

• Optimized polycarbosilane via utilizing a small amount of polypropylene was used directly in fused deposition modeling. • 3D precursor scaffolds with few defects and spanning structures were successfully obtained via fused deposition modeling. • SiO x C y ceramics with satisfactory strength were obtained via the polymer precursor routes. 3D structured ceramics stemmed from preceramic polymers via additive manufacturing have attracted much attention recently. However, these polymers with high ceramic yield are so brittle that extrusion-based additive manufacturing techniques are hardly able to be utilized for assembling 3D structures. Herein, we developed a strategy to prepare feedstocks for these manufacturing techniques, i.e., utilizing a small amount of thermal-plastic polymer to optimize the preceramic polymer while good compatibility is required between the two polymers to ensure a homogeneous mixture. Polycarbosilane and polypropylene were selected as the representative materials. Polypropylene occupied a small proportion (≤5wt.%) and significantly improved the formability of the precursor. Three-dimensional SiC were obtained via fused deposition modeling combined with crosslinking and pyrolysis. The SiC ceramic filaments showed a mean tensile strength of 471 MPa. The strategy is also applicable to a large field of ceramic systems with corresponding precursor, such as sialon ceramic and multicomponent Si-based ceramics. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new lead-free BiFeO 3 -BaTiO 3 is designed for piezoelectric actuator applications. • A large d 33 * ∼ 772 pm/V and thermally stable Δ d 33 *(T) ∼ 26% are achieved. • The increase in tetragonality provides polar length for B-site cation displacement. • A decrease in octahedral tilting reduces anisotropy for domain switching. • The argument of high piezoelectric strain is supported by TEM, PFM and XRD results. Designing a new high-performance lead-free ceramic has become a cutting-edge research topic due to growing concerns about the toxic nature of lead-based materials. In this work, a convenient strategy of compositional design and domain engineering is applied to the lead-fee BiFeO 3 -BaTiO 3 ceramics which provides a flexible polarization free-energy profile for domain switching. Here, simultaneously enhanced dynamic piezoelectric constant (d 33 * ≈ 772 pm/V) and a good thermal-stability (Δ d 33 * ≈ 26% over the temperature of 20–180 °C) are achieved with a high Curie temperature (T C) of 432 °C. This high piezoelectric strain performance is collectively attributed to multiple effects such as thermal quenching, suppression of defect charges by donor doping, chemically induced local structure heterogeneity, and electric field-induced phase transition. Furthermore, the addition of BT content decreased octahedral tilting that reduce anisotropy for domain switching and increased in tetragonality (c T / a T) providing a wider polar length for B-site cation displacement, leading to high piezoelectric strain performance. Atomic-resolution transmission electron microscopy and piezoelectric force microscopy combined with X-ray diffraction results strongly support the origin of high piezoelectricity. The high and temperature-stable piezoelectric strain response of this work is superior to those of other lead-free ceramics. The synergistic approach of composition design and the concept present here for the origin of high strain response provides a paradigm for the development of new materials for high-temperature piezoelectric actuator applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • 0–3 type composite structure is achieved in the BNT-SBT-ZnO ceramics. • ZnO not only acts as a sintering aid, but also enhances the random fields and polar nanoregions activity by Zn2+ doping. • Obvious element segregation is generated in the BNT-based matrix grains showing different Sr2+/(Bi3+, Na+) ratios. • Optimized energy storage performance is realized with W rec ∼ 5.84 J/cm3, η ∼ 93 %, and E B ∼ 40 kV/mm. In this work, ZnO is introduced into the 0.55Bi 0.5 Na 0.5 TiO 3 -0.45Sr 0.7 Bi 0.2 □ 0.1 TiO 3 (BNT-SBT) to optimize the dielectric energy storage performance. ZnO is not only used as a sintering aid to decrease the sintering temperature and ceramic grain size, but also enhances the random fields and polar nanoregions activity in the ceramics by Zn2+ doping. Intriguingly, the ZnO-modified BNT-SBT ceramics present a 0–3 type composite structure containing the TiZn 2 O 4 and Bi 2 Ti 2 O 7 linear dielectrics. Moreover, obvious element segregation is generated in the BNT-based matrix grains showing different Sr2+/(Bi3+, Na+) ratios and polarization magnitudes. The significant variations in composition distribution, grain and domain configurations cause the overall optimization of energy storage properties, reflected in the enhanced breakdown strength, delayed polarization saturation, and reduced polarization hysteresis. As a result, the optimized W rec ∼ 5.84 J/cm3 and η ∼ 93 % at 40 kV/mm is obtained in the BNT-SBT-0.10ZnO ceramic, superior to that of the BNT-SBT ceramic (W rec ∼ 3.35 J/cm3 and η ∼ 89 % at 28 kV/mm). [ABSTRACT FROM AUTHOR]

• KTaO 3 modified Na 0.5 Bi 0.5 TiO 3 ceramics are synthesized for dielectric and energy storage capacitors. • The dielectric constant variation of the 0.90NBT-0.10KT ceramic is less than 15% in the range of 29–390 °C. • A large discharge energy density W D of 2.8 J/cm3 and energy efficiency of η 80.4% are achieved for 0.80NBT-0.20KT ceramic. Nowadays, it remains a challenge to achieve a simultaneous improvement of dielectric constant, energy density, and temperature stability in dielectric ceramics. In this work, it was found that such drawback could be effectively resolved by using KTaO 3 to substitute Na 0.5 Bi 0.5 TiO 3. In (1- x)Na 0.5 Bi 0.5 TiO 3 - x KTaO 3 ceramics, the temperature coefficient of capacitance (TCC) of x = 0.10 composition is lower than 15% in the temperature range of 25–390 °C, with a high dielectric constant of 2008 and a low dielectric loss of 0.0044 at 150 °C. Meanwhile, a large discharged energy density of ~2.50 J/cm3 with the variation less than± 3% in 5–190 °C was obtained under a low electric field of 18 kV/mm in x = 0.20 composition, accompanied with a high energy efficiency of> 80%. These results reveal that this ceramic system is a promising candidate for temperature-stable dielectric and energy storage capacitors applications. [ABSTRACT FROM AUTHOR]