Giant Energy Density via Mechanically Tailored Relaxor Ferroelectric Behavior of PZT Thick Film.

Relaxor ferroelectrics (RFEs) are being actively investigated for energy-storage applications due to their large electric-field-induced polarization with slim hysteresis and fast energy charging-discharging capability. Here, a novel nanograin engineering approach based upon high kinetic energy deposition is reported, for mechanically inducing the RFE behavior in a normal ferroelectric Pb(Zr0.52 Ti0.48 )O3 (PZT), which results in simultaneous enhancement in the dielectric breakdown strength (EDBS ) and polarization. Mechanically transformed relaxor thick films with 4 µm thickness exhibit an exceptional EDBS of 540 MV m-1 and reduced hysteresis with large unsaturated polarization (103.6 µC cm-2 ), resulting in a record high energy-storage density of 124.1 J cm-3 and a power density of 64.5 MW cm-3 . This fundamental advancement is correlated with the generalized nanostructure design that comprises nanocrystalline phases embedded within the amorphous matrix. Microstructure-tailored ferroelectric behavior overcomes the limitations imposed by traditional compositional design methods and provides a feasible pathway for realization of high-performance energy-storage materials.

Molten-Salt Processed Potassium Sodium Niobate Single-Crystal Microcuboids with Dislocation-Induced Nanodomain Structures and Relaxor Ferroelectric Behavior.

We herein report a facile molten-salt synthetic strategy to prepare transparent and uniform Li, Ba-doped (K,Na)NbO3 (KNN) single-crystal microcuboids (∼80 µm). By controlling the degree of supersaturation, different growth modes were found and the single-crystal microcuboids were synthesized via island-like oriented attachment of KNN particles onto the growing surface. The distinct relaxor ferroelectric (RFE) properties were achieved in the single-crystal microcuboids, which were different from the normal ferroelectric (FE) properties found in their KNN ceramic counterparts prepared through a solid-state reaction using the same initial precursors. The RFE properties were realized by dislocation-induced nanodomain formation during oriented attachment growth of single-crystal microcuboids, which is different from the current strategies to derive the nanodomains by the local compositional inhomogeneity or the application of an electric field. The dislocations served as nucleation sites for ferroelectric domain walls and block the growth of domains. The KNN single-crystal microcuboids exhibited a higher effective piezoelectric coefficient (∼459 pm/V) compared to that of the bulk KNN ceramic counterpart (∼90 pm/V) and showed the broad diffuse maxima in the temperature dependence dielectric permittivity. The high maximum polarization (69.6 µC/cm2) at a relatively low electric field (30 kV/cm) was beneficial for energy storage applications. Furthermore, the KNN-based transparent, flexible pressure sensor directly monitored the mechanical motion of human activity without any external electric power. This study provides insights and synthetic strategies of single-crystal RFE microcuboids for other different perovskites, in which nanodomain structures are primarily imposed by their chemical composition.

Supraparticle Engineering for Highly Dense Microspheres: Yttria-Stabilized Zirconia with Adjustable Micromechanical Properties.

Various supraparticles have been extensively studied owing to their excellent catalytic properties that are attributed to their inherent porous structure; however, their mechanical properties have not garnered attention owing to their less dense structure. We demonstrate a rational approach for fabricating assembled supraparticles and, subsequently, highly dense microspheres. In addition, 3 mol % yttria-stabilized zirconia (3YSZ) and alumina particles were selected as building blocks and assembled into higher-order architectures using a droplet-based template method (spray drying) for validation with proof-of-concept. Moreover, structural features such as density, size, sphericity, and morphology of supraparticles were controlled by adjusting the competing kinetics occurring between the assembly of building blocks and evaporation of the solvent in the droplets. The preparatory aqueous suspension and process parameters were optimized as well. A detailed understanding of the formation mechanism facilitated the yield of tailor-made supraparticles and, thereafter, highly dense microspheres (approximate relative density = 99%) with excellent sphericity (>98%) via heat treatment. The microspheres displayed highest hardness (26.77 GPa) and superior elastic modulus (210.19 GPa) compared with the mechanical properties of the 3YSZ samples reported to date. Ultimately, the proposed supraparticle engineering provided insight for controlling the structural features and resultant micromechanical properties, which widely extends the applicability of supraparticle-based functional materials for practical purposes that require materials with high density and excellent mechanical properties.

Multiscale surface modified magneto-mechano-triboelectric nanogenerator enabled by eco-friendly NaCl imprinting stamp for self-powered IoT applications.

In this paper, we demonstrated a multiscale micro- and nano-structured magneto-mechano-triboelectric nanogenerator (MMTENG) enabled by a salt particle imprinting process to power an internet of thing (IoT) sensor. The fine salt particles were utilized to form a multiscale structure on a triboelectric polymer film by mechanical pressure via an eco-friendly, low-cost, and simple process, thereby reinforcing the contact triboelectrification and electrostatic induction. The surface modified MMTENG can generate an open-circuit peak-to-peak voltage of 851 V, a short-circuit current of 155 µA, and a maximum peak power of 10.3 mW under an AC magnetic field of 8 Oe. The energy device also presented output stability over 124 million operating cycles. Finally, the electricity of the surface enhanced MMTENG device was directly utilized to power an IoT temperature sensor with integration of an energy harvester, energy conversion circuit, and storage capacitor.

Selective Phase Control of Dopant-Free Potassium Sodium Niobate Perovskites in Solution.

As one of the perovskite families, potassium sodium niobates (K1-xNax)NbO3 (KNN) have been gaining tremendous attention due to their various functional properties which can be largely determined by their crystallographic phase and composition. However, a selective evolution of different phases for KNN with controlled composition can be difficult to achieve, especially in solution chemical synthesis because of its strong tendency to stabilize into orthorhombic phase at conventional synthetic temperature. We herein developed a facile solution approach to control the phase and composition of dopant-free KNN particles selectively through the modification of reaction parameters. A conventional hydrothermal synthesis method yielded orthorhombic KNN particles, while the monoclinic phase, which has never been observed in a bulk counterpart, was kinetically generated by the compositional modification of an intermediate phase under a high-intensity ultrasound irradiation. Cubic KNN particles were stabilized when ethylene glycol was used as a co-solvent together with deionized water through bonding between ethylene glycol molecules and the surface of the KNN. Composite-structured piezoelectric harvesters were fabricated using each phase of KNN particles and the ß-phase poly(vinylidene fluoride-co-trifluoroethylene) polymer. Maximum output power was found for the harvester containing orthorhombic KNN particles. This facile synthetic methodology could pave a new pathway for fabricating numerous phase-controlled materials.

A Comparison Study of Fatigue Behavior of Hard and Soft Piezoelectric Single Crystal Macro-Fiber Composites for Vibration Energy Harvesting.

Designing a piezoelectric energy harvester (PEH) with high power density and high fatigue resistance is essential for the successful replacement of the currently using batteries in structural health monitoring (SHM) systems. Among the various designs, the PEH comprising of a cantilever structure as a passive layer and piezoelectric single crystal-based fiber composites (SFC) as an active layer showed excellent performance due to its high electromechanical properties and dynamic flexibilities that are suitable for low frequency vibrations. In the present study, an effort was made to investigate the reliable performance of hard and soft SFC based PEHs. The base acceleration of both PEHs is held at 7 m/s2 and the frequency of excitation is tuned to their resonant frequency (fr) and then the output power (Prms) is monitored for 107 fatigue cycles. The effect of fatigue cycles on the output voltage, vibration displacement, dielectric, and ferroelectric properties of PEHs was analyzed. It was noticed that fatigue-induced performance degradation is more prominent in soft SFC-based PEH (SS-PEH) than in hard SFC-based PEH (HS-PEH). The HS-PEH showed a slight degradation in the output power due to a shift in fr, however, no degradation in the maximum power was noticed, in fact, dielectric and ferroelectric properties were improved even after 107 vibration cycles. In this context, the present study provides a pathway to consider the fatigue life of piezoelectric material for the designing of PEH to be used at resonant conditions for long-term operation.

Enhancement of Magnetoelectric Conversion Achieved by Optimization of Interfacial Adhesion Layer in Laminate Composites.

We report the effect of epoxy adhesion layers with different mechanical or physical property on a magnetoelectric (ME) composite laminate composed of FeBSi alloy (Metglas)/single-crystal Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3/Metglas to achieve an improved ME conversion performance. Through theoretical simulation, it was revealed that the Young's modulus and the thickness of interfacial adhesives were major parameters that influence the conversion efficiency in ME composites. In the experimental evaluation, we utilized three epoxy materials with a distinct Young's modulus and adjusted the average thickness of the adhesion layers to optimize the ME conversion. The experimental results show that a thin epoxy layer with a high Young's modulus provided the best performance in the inorganic-based ME conversion process. By tailoring the interfacial adhesion property, the ME laminate generated a high conversion coefficient of 328.8 V/(cm Oe), with a mechanical quality factor of 132.0 at the resonance mode. Moreover, we demonstrated a highly sensitive alternating current magnetic field sensor that had a detection resolution below 10 pT. The optimization of the epoxy layers in the ME laminate composite provided significant enhancement of the ME response in a simple manner.

Next Generation Ceramic Substrate Fabricated at Room Temperature.

A ceramic substrate must not only have an excellent thermal performance but also be thin, since the electronic devices have to become thin and small in the electronics industry of the next generation. In this manuscript, a thin ceramic substrate (thickness: 30-70 µm) is reported for the next generation ceramic substrate. It is fabricated by a new process [granule spray in vacuum (GSV)] which is a room temperature process. For the thin ceramic substrates, AlN GSV films are deposited on Al substrates and their electric/thermal properties are compared to those of the commercial ceramic substrates. The thermal resistance is significantly reduced by using AlN GSV films instead of AlN bulk-ceramics in thermal management systems. It is due to the removal of a thermal interface material which has low thermal conductivity. In particular, the dielectric strengths of AlN GSV films are much higher than those of AlN bulk-ceramics which are commercialized, approximately 5 times. Therefore, it can be expected that this GSV film is a next generation substrate in thermal management systems for the high power application.

Self-Growth of Centimeter-Scale Single Crystals by Normal Sintering Process in Modified Potassium Sodium Niobate Ceramics.

In this manuscript, an interesting phenomenon is reported. That is the self-growth of single crystals in Pb-free piezoelectric ceramics. These crystals are several centimeters in size. They are grown without any seed addition through a normal sintering process in modified potassium sodium niobate ceramics. It has been achieved by the composition designed to compensate the Na(+) loss which occurs during the liquid phase sintering. The composition of the crystals is (K0.4925Na(0.4925-x)Ba(0.015+x/2))Nb(0.995+x)O3 [x is determined by the Na(+) loss, due to Na2O volatilization]. These crystals have high piezoelectric voltage coefficients (g33, 131 10(-3)Vm/N), indicating that they are good candidates for piezoelectric sensors and energy harvesting devices. We hope that this report can offer the opportunity for many researchers to have an interest in these crystals.

Upshift of phase transition temperature in nanostructured PbTiO3 thick film for high temperature applications.

Thick polycrystalline pure PbTiO3 films with nano size grains were synthesized for the first time by aerosol deposition. Annealed 7 µm thick films exhibit well-saturated ferroelectric hysteresis loops with a remanent polarization and coercive field of 35 µC/cm(2) and 94 kV/cm, respectively. A large-signal effective d33,eff value of >60 pm/V is achieved at room temperature. The measured ferroelectric transition temperature (Tc) of the films ∼550 °C is >50 °C higher than the reported values (∼490 °C) for PbTiO3 ceramics. First-principles calculations combined with electron energy loss spectroscopy (EELS) and structural analysis indicate that the film is composed of nano size grains with slightly decreased tetragonality. There is no severe off-stoichiometry, but a high compressive in-plane residual stress was observed in the film along with a high transition temperature and piezoelectric response. The ferroelectric characteristics were sustained until 200 °C, providing significant advancement toward realizing high temperature piezoelectric materials.

Effect of NiZnFeO4 content on PZT-pZN + NiZnFeO4 magnetoelectric composite.

We fabricated and characterized the magnetoelectric (ME) properties of 3-0 ME composite materials comprised of the high piezoelectric voltage coefficient material, 0.9Pb(Zr0.52Ti0.48)O3-0.1 Pb(Zn1/3Nb2/3)O3 + 0.005Mn (PZT-PZN), and the magnetostrictive material, Ni0.8Zn0.2Fe2O4 (NZF). As the ME effect is generated by the product coupling between the piezoelectric properties and the magnetostrictive properties, the NZF content should be optimized for a higher ME coefficient. The dielectric constant and spontaneous polarization (P) were decreased with increasing NZF content before the percolation of the NZF particulates. However, as the NZF content exceeded the percolation content, the dielectric loss was dramatically increased due to the low resistivity of NZF. While the piezoelectric constant was decreased with increasing NZF content, the maximum magnetization was linearly increased. When we combined the piezoelectric and magnetostrictive effects, the ME composite sintered at 1200 degrees C with 20% NZF showed a maximum dE/dH of 27 mV/cm x Oe at a magnetic bias of 1240 Oe.

Mechanical and in vitro biological performances of hydroxyapatite-carbon nanotube composite coatings deposited on Ti by aerosol deposition.

Hydroxyapatite (HA)-carbon nanotube (CNT) composite coatings on Ti plate, produced by aerosol deposition using HA-CNT powders, were developed for biomedical applications. For the deposition process HA-CNT powder mixtures with CNT contents of 1 and 3 wt.% were used. Dense coatings with a thickness of 5 microm were fabricated, irrespective of the content of CNTs. No pores or microcracks were observed in the coatings. The coatings had good adhesion to the substrate, exhibiting a high adhesion strength, ranging from 27.3 to 29.0 MPa. Microstructural observation using field-emission gun scanning electron microscopy and transmission electron microscopy showed that CNTs with a typical tubular structure were found in the HA-CNT composite coatings. Nanoindentation tests revealed that the mechanical properties, such as the hardness and elastic modulus, were significantly improved by the addition of the CNTs to the HA coating. In addition, the proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 pre-osteoblast cells grown on the HA-CNT composite coatings were higher than those on the bare Ti and pure HA coating. The ALP activity of the composite coatings considerably improved as the CNT content increased. These results suggest that CNTs would be an effective reinforcing agent to enhance both the mechanical and biological performances of HA coatings.

Sintering and piezoelectric properties of KNN ceramics doped with KZT.

This paper investigates the effect of K(1.94)Zn(1.06)Ta(5.19)O(15) (KZT) addition on the sintering behavior and piezoelectric properties in lead free piezoelectric ceramics of (K(0.5)Na(0.5))NbO(3) (KNN). The apparent density of sintered KNN ceramics was increased with KZT addition, and a relative density of above 96.3% was obtained with the doping of over 0.5 mol% KZT. The maximum dielectric and piezoelectric properties of epsilon(T)(3)/epsilon(0) = 590, d(33) = 126 pC/N, k(p) = 0.42, and P(r) = 18 microC/cm(2) were obtained from 0.5 mol% KZT-doped KNN ceramics. A small amount of KZT (about 0.5 mol%) was effective for improving the sintering behavior and piezoelectric properties, but KZT addition exceeding 1.0 mol% was effective only for densification. A small amount of KZT was effective for densification of KNN ceramics by promoting K(5.75)Nb(10.8)O(30) liquid phase formation. However, even though KNN with 1.0 to approximately -2.0 mol% KZT had a relative density of >98.5%, the piezoelectric properties were inferior to those of 0.5 mol% KZT-doped KNN, presumably due to the smaller grain size and excess liquid phase of the KNN ceramics doped with higher amounts of KZT. It is believed that a small amount of KZT could be one of the suitable sintering aids to obtain highly dense KNN based piezoelectric.