Oxide-Halide Perovskite Composites for Simultaneous Recycling of Lead Zirconate Titanate Piezoceramics and Methylammonium Lead Iodide Solar Cells.

Global concerns over energy availability and the environment impose an urgent requirement for sustainable manufacturing, usage, and disposal of electronic components. Piezoelectric and photovoltaic components are being extensively used. They contain the hazardous element, Pb (e.g., in widely used and researched Pb(Zr,Ti)O3 and halide perovskites), but they are not being properly recycled or reused. This work demonstrates the fabrication of upside-down composite sensor materials using crushed ceramic particles recycled from broken piezoceramics, polycrystalline halide perovskite powder collected from waste dye-sensitized solar cells, and crystal particles of a Cd-based perovskite composition, C6 H5 N(CH3 )3 CdBr3 x Cl3(1- x ) . The piezoceramic and halide perovskite particles are used as filler and binder, respectively, to show a proof of concept for the chemical and microstructural compatibility between the oxide and halide perovskite compounds while being recycled simultaneously. Production of the recycled and reusable materials requires only a marginal energy budget while achieving a very high material densification of >92%, as well as a 40% higher piezoelectric voltage coefficient, i.e., better sensing capability, than the pristine piezoceramics. This work thus offers an energy- and environmentally friendly approach to the recycling of hazardous elements as well as giving a second life to waste piezoelectric and photovoltaic components.

Ultraelastic and High-Conductivity Multiphase Conductor with Universally Autonomous Self-Healing.

Next-generation, truly soft, and stretchable electronic circuits with material level self-healing functionality require high-performance solution-processable organic conductors capable of autonomously self-healing without external intervention. A persistent challenge is to achieve required performance level as electrical, mechanical, and self-healing properties optimized in tandem are difficult to attain. Here heterogenous multiphase conductor with cocontinuous morphology and macroscale phase separation for ultrafast universally autonomous self-healing with full recovery of pristine tensile and electrical properties in less than 120 and 900 s, respectively, is reported. The multiphase conductor is insensitive to flaws under stretching and achieves a synergistic combination of conductivity up to ≈1.5 S cm-1 , stress at break ≈4 MPa, toughness up to >81 MJ m-3 , and elastic recovery exceeding 2000% strain. Such properties are difficult to achieve simultaneously with any other type of material so far. The solution-processable multiphase conductor offers a paradigm shift for damage tolerant and environmentally resistant soft electronic components and circuits with material level self-healing.

Piezoelectric Energy Harvesting from Rotational Motion to Power Industrial Maintenance Sensors.

In industry, forecasting machinery failures could save significant time and money if any maintenance breaks are predictable. The aim of this work was to develop an energy harvesting system which could, in theory, power condition monitoring sensors in heavy machinery. In this study, piezoelectric-cantilever-type energy harvesters were attached to a motor and spun around with different rotational speeds. A mass was placed on the tip of the cantilevers, which were mounted pointing inward toward the center axis of the motor. Pointing a cantilever tip inward and increasing the distance from the center axis of the motor decreased the natural resonance frequency significantly and thus enabled higher harvested energy levels with lower rotational frequencies. Motion of the cantilever was also controlled by altering the movement space of the tip mass. This created another possibility to control the cantilever dynamics and prevent overstressing of the piezoelectric material. Restricting the movement of the tip mass can also be used to harvest energy over a wider frequency range and prevent the harvester from getting trapped into a stagnant position. The highest calculated raw power of 579.2 µW at 7.4 Hz rotational frequency was measured from a cantilever with outer dimensions of 25 mm × 100 mm. Results suggest that an energy harvesting system with multiple cantilevers could be designed to replace batteries in condition sensors monitoring revolving machinery.

Design and Fabrication of a C-Band Dielectric Resonator Antenna with Novel Temperature-Stable Ce(Nb1-xVx)NbO4 (x = 0-0.4) Microwave Ceramics.

Vanadium(V)-substituted cerium niobate [Ce(Nb1-xVx)O4, CNVx] ceramics were prepared to explore their structure-microwave (MW) property relations and application in C-band dielectric resonator antennas (DRAs). X-ray diffraction and Raman spectroscopy revealed that CNVx (0.0 ≤ x ≤ 0.4) ceramics exhibited a ferroelastic phase transition at a critical content of V (xc = 0.3) from a monoclinic fergusonite structure to a tetragonal scheelite structure (TF-S), which decreased in temperature as a function of x according to thermal expansion analysis. Optimum microwave dielectric performance was obtained for CNV0.3 with permittivity (εr) of ∼16.81, microwave quality factor (Qf) of ∼41 300 GHz (at ∼8.7 GHz), and temperature coefficient of the resonant frequency (TCF) of ∼ -3.5 ppm/°C. εr is dominated by Ce-O phonon absorption in the microwave band; Qf is mainly determined by the porosity, grain size, and proximity of TF-S; and TCF is controlled by the structural distortions associated with TF-S. Terahertz (THz) (0.20-2.00 THz, εr ∼ 12.52 ± 0.70, and tan δ ∼ 0.39 ± 0.17) and infrared measurements are consistent, demonstrating that CNVx (0.0 ≤ x ≤ 0.4) ceramics are effective in the sub-millimeter as well as MW regime. A cylindrical DRA prototype antenna fabricated from CNV0.3 resonated at 7.02 GHz (|S11| = -28.8 dB), matching simulations, with >90% radiation efficiency and 3.34-5.93 dB gain.

All-Around Universal and Photoelastic Self-Healing Elastomer with High Toughness and Resilience.

Ultimately soft electronics seek affordable and high mechanical performance universal self-healing materials that can autonomously heal in harsh environments within short times scales. As of now, such features are not found in a single material. Herein, interpenetrated elastomer network with bimodal chain length distribution showing rapid autonomous healing in universal conditions (<7200 s) with high efficiency (up to 97.6 ± 4.8%) is reported. The bimodal elastomer displays strain-induced photoelastic effect and reinforcement which is responsible for its remarkable mechanical robustness (≈5.5 MPa stress at break and toughness ≈30 MJ m-3 ). The entropy-driven elasticity allows an unprecedented shape recovery efficiency (100%) even after fracturing and 100% resiliency up to its stretching limit (≈2000% strain). The elastomers can be mechanically conditioned leading to a state where they recover their shape extremely quickly after removal of stress (nearly order of magnitude faster than pristine elastomers). As a proof of concept, universal self-healing mechanochromic strain sensor is developed capable of operating in various environmental conditions and of changing its photonic band gap under mechanical stress.

Ultra-low permittivity porous silica-cellulose nanocomposite substrates for 6G telecommunication.

The continuously increasing demand for faster data traffic of our telecommunication devices requires new and better materials and devices that operate at higher frequencies than today. In this work, a porous composite of silica nanoshells and cellulose nanofibers is demonstrated as a suitable candidate of dielectric substrates to be used in future 6G frequency bands. The hollow nanospheres of amorphous SiO2 with outstanding electromagnetic properties were obtained by a template-assisted Stöber process, in which a thin shell of silica is grown on polystyrene nanospheres first, and then the polymer core is burned off in a subsequent step. To be able to produce substrates with sufficient mechanical integrity, the nanoshells of SiO2 were reinforced with cellulose nanofibers resulting in a porous composite of very low mass density (0.19 ± 0.02 g cm-3), which is easy to press and mold to form films or slabs. The low relative dielectric permittivity (ε r = 1.19 ± 0.01 at 300 GHz and ε r = 1.17 ± 0.01 at 2.0 THz) and corresponding loss tangent (tan δ= 0.011 ± 0.001 at 300 GHz and tan δ = 0.011 ± 0.001 at 2.0 THz) of the composite films are exploited in substrates for radio frequency filter structures designed for 300 GHz operation.

Stretchable Sensors with Tunability and Single Stimuli-Responsiveness through Resistivity Switching Under Compressive Stress.

The fascinating human somatosensory system with its complex structure is composed of numerous sensory receptors possessing distinct responsiveness to stimuli. It is a continuous source of inspiration for tactile sensors that mimic its functions. However, to achieve single stimulus-responsiveness with mechanical decoupling is particularly challenging in the light of structural design and has not been fully addressed to date. Here we propose a novel structural design inspired by combining the characteristics of electronic skin (e-skin) and electronic textile (e-textile) into a hybrid interface to achieve a stretchable single stimuli-responsive tactile sensor. The stencil printable biocarbon composite/silver-plated nylon hybrid interface possesses an extraordinary resistance switching (ΔR/R0 up to ∼104) under compressive stress which is controllable by the composite film-thickness. It achieves a very high normal pressure sensitivity (up to 60.8 kPa-1) in a wide dynamic range (up to ∼50 kPa) in the piezoresistive operation mode and can effectively decouple stresses induced by stretching or bending. In addition, the device is capable of high accuracy strain sensing in its capacitive operation mode through dimensional change dominant response. Because of these intriguing features, it has potential for the next-generation Internet of Things devices and user-interactive systems capable of providing visual feedback and more advanced robotics or even prosthetics.

A Temperature-Responsive Copper Molybdate Polymorph Mixture near to Water Boiling Point by a Simple Cryogenic Quenching Route.

Smart temperature-responsive inorganic materials in accessible temperature ranges open up new positions in the technology. Herein, we present for the first time a CuMoO4 polymorph mixture prepared by a simple cryogenic quenching approach, which offers a fast temperature response close to water boiling temperature for use as a permanent temperature recorder. The new cryogenic quenching technique initiates the formation of a unique polymorph mixture of a deep brown color with a nonuniform combination of γ- and α-CuMoO4, with the γ phase being confined to the outer region of α-CuMoO4, which has been prepared by conventional solid-state synthesis. In situ structural analysis and refinement results confirm the presence of CuMoO4 α and γ polymorphs in which the amount of γ polymorph decreases and that of the α phase increases with temperature, accounting for the irreversible thermochromic behavior. The thermal analysis reveals that the polymorph mixture exhibits a fast response with the color changing from deep brown to bright green with intermediate colors of light brown, yellowish green, and light green depending on the exposure temperature as observed from reflectance measurements.

Ultra-Low-Temperature Cofired Ceramic Substrates with Low Residual Carbon for Next-Generation Microwave Applications.

High-temperature cofired ceramics and low-temperature cofired ceramics are important technologies in the fabrication of multilayer ceramic substrates for discrete devices, electronics packages, and telecommunications. However, there is a place and need for materials with lower fabrication temperatures to decrease the associated energy consumption. The present paper studies the feasibility of two ultra-low sintering temperature cofired ceramic materials, copper molybdate and copper molybdate-Ag2O, sinterable at 650 and 500 °C, respectively, for multilayer substrates using tape casting. The slurry composition developed uses environmentally friendly organics and a nontoxic binder and solvent. Additionally, the green cast tapes exhibit very low residual carbon (less than 5%) after sintering on analysis by X-ray photoelectron spectroscopy. The multilayer substrates show a permittivity value of about 8 with a low dielectric loss in the range of 10-5 to 10-4 in the frequency range of 2-10 GHz along with a low coefficient of thermal expansion in the range of 4-5 ppm/°C and good compatibility with an Al electrode. Thus, these proposed substrates have much promise, with good thermal, mechanical, and dielectric properties comparable to commercial substrates while also providing an energy and environment-friendly solution.

Lightweight Hierarchical Carbon Nanocomposites with Highly Efficient and Tunable Electromagnetic Interference Shielding Properties.

High-performance electromagnetic interference shielding is becoming vital for the next generation of telecommunication and sensor devices among which portable and wearable applications require highly flexible and lightweight materials having efficient absorption-dominant shielding. Herein, we report on lightweight carbon foam-carbon nanotube/carbon nanofiber nanocomposites that are synthesized in a two-step robust process including a simple carbonization of open-pore structure melamine foams and subsequent growth of carbon nanotubes/nanofibers by chemical vapor deposition. The microstructure of the nanocomposites resembles a 3-dimensional hierarchical network of carbonaceous skeleton surrounded with a tangled web of bamboo-shaped carbon nanotubes and layered graphitic carbon nanofibers. The microstructure of the porous composite enables absorption-dominant (absorbance ∼0.9) electromagnetic interference shielding with an effectiveness of ∼20-30 dB and with an equivalent mass density normalized shielding effectiveness of ∼800-1700 dB cm3 g-1 at the K-band frequency (18-26.5 GHz). Moreover, the hydrophobic nature of the materials grants water-repellency and stability in humid conditions important for reliable operation in outdoor use, whereas the mechanical flexibility and durability with excellent piezoresistive behavior enable strain-responsive tuning of electrical conductivity and electromagnetic interference shielding, adding on further functionalities. The demonstrated nanocomposites are versatile and will contribute to the development of reliable devices not only in telecommunication but also in wearable electronics, aerospace engineering, and robotics among others.

Ferroelectric Oxides for Solar Energy Conversion, Multi-Source Energy Harvesting/Sensing, and Opto-Ferroelectric Applications.

Photoferroelectrics belong to a unique material family that exhibits both photovoltaic and ferroelectric effects simultaneously. The photovoltaic effect is the only known direct method of converting light into electricity and is the basis of solar cells. The ferroelectric effect can induce piezoelectric and pyroelectric effects, which are the working principles of widely used kinetic and thermal sensors, transducers, actuators, and energy harvesters. For a long time, photoferroelectric research was restricted to theoretical investigations only because of either the wide band gap (Eg ), which is not able to effectively absorb visible light, or to the weak ferroelectricity caused by a narrow Eg . Recent scientific breakthroughs, however, have opened doors for the development of practical applications. In this article, emerging concepts of creating balanced photovoltaic and ferroelectric properties for photoferroelectrics, as well as those of novel applications in future devices, are presented.

ULTCC Glass Composites Based on Rutile and Anatase with Cofiring at 400 °C for High Frequency Applications.

The article presents the very first materials to the ultralow temperature cofired ceramic (ULTCC) technology with the sintering temperature of 400 °C. The dielectric composites are based on a rutile and anatase with commercial GO17 sealing glass. In addition to the bulk samples, the tape casting procedure is also introduced to show its feasibility to cofiring with commercial Ag electrodes at 400 °C. The structural, microstructural, thermal, and microwave dielectric properties in the green and sintered samples were investigated. The optimum amount of glass to fabricate substrates was found to be 30 vol %. The ULTCC substrates with the anatase TiO2A-30GO17 and rutile TiO2R-30GO17 that were sintered at 400 °C showed a relative permittivity of 9.9 and 15 and a dielectric loss of 0.006 and 0.003, respectively, at the measurement frequency of 9.9 GHz. The temperature dependences of the relative permittivity were +70 and -400 ppm/°C, respectively. Moreover, the coefficients of the thermal expansion of the substrates were 7.4 and 8.3 ppm/°C in the measured temperature range of 50-300 °C. A preliminary test to study the feasibility of the anatase TiO2A-30GO17 for a dual band antenna was performed due its relatively stable temperature behavior.

Boosting Photovoltaic Output of Ferroelectric Ceramics by Optoelectric Control of Domains.

Photo-ferroelectric single crystals and highly oriented thin-films have been extensively researched recently, with increasing photovoltaic energy conversion efficiency (from 0.5% up to 8.1%) achieved. Rare attention has been paid to polycrystalline ceramics, potentially due to their negligible efficiency. However, ceramics offer simple and cost-effective fabrication routes and stable performance compared to single crystals and thin-films. Therefore, a significantly increased efficiency of photo-ferroelectric ceramics contributes toward widened application areas for photo-ferroelectrics, e.g., multisource energy harvesting. Here, all-optical domain control under illumination, visible-range light-tunable photodiode/transistor phenomena and optoelectrically tunable photovoltaic properties are demonstrated, using a recently discovered photo-ferroelectric ceramic (K0.49Na0.49Ba0.02)(Nb0.99Ni0.01)O2.995. For this monolithic material, tuning of the electric conductivity independent of the ferroelectricity is achieved, which previously could only be achieved in organic phase-separate blends. Guided by these discoveries, a boost of five orders of magnitude in the photovoltaic output power and energy conversion efficiency is achieved via optical and electrical control of ferroelectric domains in an energy-harvesting circuit. These results provide a potentially supplementary approach and knowledge for other photo-ferroelectrics to further boost their efficiency for energy-efficient circuitry designs and enable the development of a wide range of optoelectronic devices.

3D printed dielectric ceramic without a sintering stage.

This paper presents for the first time the fabrication of dielectric ceramic parts by 3D printing without sintering. The printable paste was prepared by mixing a carefully selected amount of water-soluble Li2MoO4 powder with water. A viscous mixture of solid ceramic particles and saturated aqueous phase was formed with a solid content of 60.0 vol.%. Printing of the sample discs was conducted with material extrusion using a low-cost syringe-style 3D printer. The consolidation and densification of the printed parts occurred during both printing and drying of the paste due to extrusion pressure, capillary forces, and recrystallization of the dissolved Li2MoO4. Complete drying of the paste was ensured by heating at 120 °C. The microstructure showed no delamination of the printed layers. Relatively high densities and good dielectric properties were obtained, especially when considering that no sintering and only pressure from the extrusion was employed. This approach is expected to be feasible for similar ceramics and ceramic composites.

Stretchable and Washable Strain Sensor Based on Cracking Structure for Human Motion Monitoring.

Stretchable and wearable strain sensors have been intensively studied in recent years for applications in human motion monitoring. However, achieving a high-performance strain sensor with high stretchability, ultra-sensitivity, and functionality, such as tunable sensing ranges and sensitivity to various stimuli, has not yet been reported, even though such sensors have great importance for the future applications of wearable electronics. Herein, a novel and versatile strain sensor based on a cracking (silver ink patterned silicone elastomer)-(silver plated nylon structure) (Ag-DS/CF) has been designed and fabricated. The unique structure combined precisely shaped stretchable conductive fabrics and wrinkled Ag-ink pattern to achieve an excellent electrical performance. The Ag-DS/CF could be used to detect both large and subtle human motions and activities, pressure changes, and physical vibrations by achieving high stretchability up to 75%, ultrahigh sensitivity (gauge factor >104-106), tunable sensing ranges (from 7 to 75%). Excellent durability was demonstrated for human motion monitoring with machine washability. The extremely versatile Ag-DS/CF showed outstanding potential for the future of wearable electronics in real-time monitoring of human health, sports performance, etc.

Energy Harvesting Research: The Road from Single Source to Multisource.

Energy harvesting technology may be considered an ultimate solution to replace batteries and provide a long-term power supply for wireless sensor networks. Looking back into its research history, individual energy harvesters for the conversion of single energy sources into electricity are developed first, followed by hybrid counterparts designed for use with multiple energy sources. Very recently, the concept of a truly multisource energy harvester built from only a single piece of material as the energy conversion component is proposed. This review, from the aspect of materials and device configurations, explains in detail a wide scope to give an overview of energy harvesting research. It covers single-source devices including solar, thermal, kinetic and other types of energy harvesters, hybrid energy harvesting configurations for both single and multiple energy sources and single material, and multisource energy harvesters. It also includes the energy conversion principles of photovoltaic, electromagnetic, piezoelectric, triboelectric, electrostatic, electrostrictive, thermoelectric, pyroelectric, magnetostrictive, and dielectric devices. This is one of the most comprehensive reviews conducted to date, focusing on the entire energy harvesting research scene and providing a guide to seeking deeper and more specific research references and resources from every corner of the scientific community.

Multilayer Functional Tapes Cofired at 450 °C: Beyond HTCC and LTCC Technologies.

This paper reports the first ultralow sintering temperature (450 °C) cofired multifunctional ceramic substrate based on a commercial lead zirconium titanate (PZ29)-glass composite, which is fabricated by tape casting, isostatic lamination, and sintering. This substrate was prepared from a novel tape casting slurry composition suitable for cofiring at low temperatures with commercial Ag electrodes at 450 °C. The green cast tape and sintered substrate showed a surface roughness of 146 and 355 nm, respectively, suitable for device-level fabrication by postprocessing. Additionally, the ferroelectric and piezoelectric studies disclosed low remnant polarization due to the dielectric glass matrix with average values of piezoelectric coefficient (+ d33) and voltage coefficient (+ g33) of 17 pC/N and 30 mV/N, respectively. The dielectric permittivity and loss value of the sintered substrates were 57.8 and 0.05 respectively, at 2.4 GHz. The variation of relative permittivity on temperature dependence in the range of -40 to 80 °C was about 23%, while the average linear coefficient of thermal expansion was 6.9 ppm/°C in the measured temperature range of 100-300 °C. Moreover, the shelf life of the tape over 28 months was studied through measurement of the stability of the dielectric properties over time. The obtained results open up a new strategy for the fabrication of next-generation low-cost functional ceramic devices prepared at an ultralow temperature in comparison to the high-temperature cofired ceramic and low-temperature cofired ceramic technologies.

A Game Changer: A Multifunctional Perovskite Exhibiting Giant Ferroelectricity and Narrow Bandgap with Potential Application in a Truly Monolithic Multienergy Harvester or Sensor.

An ABO3 -type perovskite solid-solution, (K0.5 Na0.5 )NbO3 (KNN) doped with 2 mol% Ba(Ni0.5 Nb0.5 )O3-δ (BNNO) is reported. Such a composition yields a much narrower bandgap (≈1.6 eV) compared to the parental composition-pure KNN-and other widely used piezoelectric and pyroelectric materials (e.g., Pb(Zr,Ti)O3 , BaTiO3 ). Meanwhile, it exhibits the same large piezoelectric coefficient as that of KNN (≈100 pC N-1 ) and a much larger pyroelectric coefficient (≈130 µC m-2 K-1 ) compared to the previously reported narrow-bandgap material (KNbO3 )1-x -BNNOx . The unique combination of these excellent ferroelectric and optical properties opens the door to the development of multisource energy harvesting or multifunctional sensing devices for the simultaneous and efficient conversion of solar, thermal, and kinetic energies into electricity in a single material. Individual and comprehensive characterizations of the optical, ferroelectric, piezoelectric, pyroelectric, and photovoltaic properties are investigated with single and coexisting energy sources. No degrading interaction between ferroelectric and photovoltaic behaviors is observed. This composition may fundamentally change the working principles of state-of-the-art hybrid energy harvesters and sensors, and thus significantly increases the unit-volume energy conversion efficiency and reliability of energy harvesters in ambient environments.