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Effect of processing conditions on (Ba1-xCax)(Ti0.9Sn0.1)O3 lead-free ceramics for the enhancement of structural, humidity sensing and dielectric properties
摘要： The present study reports detailed guidelines for the preparation of high-quality perovskite (Ba1-xCax)(Ti0.9Sn0.1)O3 (BCTS) (x = 0.0–0.1) lead-free ceramics by solid state reaction. The compositions (x = 0.0–0.04) exhibit orthorhombic–tetragonal phase transition (TO-T), except x ≥ 0.06 that shows a pure tetragonal structure phase which conformed by X-ray diffraction (XRD). The microstructure and purity of the sintered ceramics were examined using scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS). Some pores existing in the grain boundary were observed at high concentrations of Ca content. Field emission scanning electron microscope (FE-SEM) was used to examine the morphology of sensing film of the calcined powder and it was prepared as a humidity sensor using screen-printing technique. All the compositions exhibited poor sensitivity toward the humidity sensing in the range of 0–98% RH at room temperature. Hot-stage microscope (HSM) has been used to investigate the sintering curve of the pure calcined powder and it was found that the suitable sintering temperature for obtaining a fully dense microstructure is 1400 °C. The highest values of permittivity (εr = 46,515, at 10 kHz) and piezoelectric coefficient (d33 = 510 pC/N) were achieved in the composition x = 0.02. The difference between alumina and platinum crucibles for the processing of the powders has been introduced, and by the aid of dispersive spectrometer analysis and it was indicated that use of alumina crucibles leads to the undesired presence of Al in the ceramics, which can be prevented by using a capped platinum crucibles.
关键词： Lead-free ceramics,Humidity sensing,Phase formation,Processing,Dielectric properties
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE 13th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS) - Singapore, Singapore (2018.4.22-2018.4.26)] 2018 IEEE 13th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS) - Self-Powered, High-Sensitive Human Cutaneous Activities Sensor
摘要： A self-powered piezoelectric sensor based on lead-free (K,Na)NbO3 (KNN) thin film for human health monitoring is presented. The sensor is fabricated on a flexible substrate and exhibits high sensitivity and stability. It can detect various physiological signals such as pulse, respiration, and body movement. The results demonstrate its potential for wearable health monitoring applications.
关键词： piezoelectric sensor,KNN thin film,health monitoring,lead-free,flexible substrate,wearable
更新于2025-09-23 15:22:29
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Lead-free Ag <sub/> 1-3 <i>x</i> </sub> La <sub/><i>x</i> </sub> NbO <sub/>3</sub> Antiferroelectric Ceramics with High Energy Storage Density and Efficiency
摘要： Environmentally benign lead-free bulk ceramics with high recoverable energy density (Wrec) are very attractive in advanced pulsed power capacitors. In this work, composition engineering was adopted by La3+ modification to improve the energy storage performance of Ag1-3xLaxNbO3 ceramics. It was found the antiferroelectric (AFE) phase was stabilized after La3+ substitution, as a result of the reduced tolerance factor t. Significant improvement of Wrec and energy storage efficiency (η) were achieved with value of 3.12 J/cm3 and 0.63 for x=0.02 at an electric field of 230 kV/cm, more than 1.5 times the value of pure AgNbO3 (Wrec=1.9 J/cm3, η=0.40). The excellent energy storage properties are resulted from the increased antiferroelectric-ferroelectric phase transition electric field (EF), ferroelectric-antiferroelectric phase transition electric field (EA) and breakdown electric field (Eb). The enhanced Eb was ascribed to the decreased grain size and increased electrical resistivity upon La3+ modification. The feature makes Ag1-3xLaxNbO3 a potential candidate for energy storage applications.
关键词： energy storage,ferroelectricity/ferroelectric materials,lead-free ceramics,dielectric materials/properties
更新于2025-09-23 15:22:29
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[ASME ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - San Francisco, California, USA (Monday 27 August 2018)] ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - Microstructural Evolution in SAC305 and SAC-Bi Solders Subjected to Mechanical Cycling
摘要： Fatigue failure of solder joints is one of the most common methods by which electronic packages fail. Electronic assemblies usually must cope with a temperature varying environment. Due to the mismatches in coefficients of thermal expansion (CTEs) of the various assembly materials, the solder joints are subjected to cyclic thermal-mechanical loading during temperature cycling. The main focus of this work is to investigate the changes in microstructure that occur in SAC305 and SAC+Bi lead free solders subjected to mechanical cycling. In this paper, we report on results for the SAC+Bi solder commonly known as SAC_Q or CYCLOMAX. Uniaxial solder specimens were prepared in glass tubes, and the outside surfaces were polished. A nanoindenter was then used to mark fixed regions on the samples for subsequent microscopy evaluation. The samples were subjected to mechanical cycling, and the microstructures of the selected fixed regions were recorded after various durations of cycling using Scanning Electron Microscopy (SEM). Using the recorded images, it was observed that the cycling induced damage consisted primarily of small intergranular cracks forming along the subgrain boundaries within dendrites. These cracks continued to grow as the cycling continued, resulting in a weakening of the dendrite structure, and eventually to the formation of large transgranular cracks. The distribution and size of the intermetallic particles in the inter-dendritic regions were observed to remain essentially unchanged.
关键词： Bismuth,Microstructure,SAC Alloy,Hysteresis,Evolution,Lead Free Solder,Cyclic Stress-Strain Curve
更新于2025-09-23 15:22:29
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Ultra-low hysteresis electric field-induced strain with high electrostrictive coefficient in lead-free Ba(Zr Ti1-)O3 ferroelectrics
摘要： From the application point of view, high electric field-induced strain with ultra-low hysteresis or hysteresis-free characteristic is highly desired in high-precision displacement actuators. In this work, lead-free Ba(ZrxTi1-x)O3 (BZT) ferroelectrics with x in the range between 0.02 and 0.1 were fabricated by a conventional solid state reaction method. The structural evolution and electrical properties were investigated systematically with an emphasis on electrostrictive effect. As x increases from 0.02 to 0.1, the crystal lattice parameters (a and c axes) increase while the tetragonality (c/a-1) goes down. In addition, the Curie temperature (TC) of BZT decreases gradually, while the temperatures corresponding to tetragonal-to-orthorhombic (T-O) and orthorhombic-to-rhombohedral (O-R) phase transitions increase. Ultra-low hysteresis (<8%) and high electric field-induced strains (>0.15% at 60 kV/cm) are observed in all studied compositions. Most importantly, a high longitudinal electrostrictive coefficient Q33 (0.0453 m4/C2) was also identified in x=0.1 composition. This work not only reports high electric field-induced strains with ultra-low hysteresis and high Q33 in lead-free BZT ferroelectrics, but also indicates a potential application for BZT ceramics in high-precision displacement actuators.
关键词： Electrostriction,Ferroelectric,Lead-free,Electric field induced strain,BZT
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - Lead-Free Sodium Potassium Niobate Based Piezoelectric Thick Film Bimorph Structure for Energy Harvesting
摘要： A novel piezoelectric ceramic-based bimorph energy harvester (PEH) is proposed in this paper for scavenging energy from low-frequency vibrations in many types of applications, such as in the human body or in industry. The PEH is based on a lead-free piezoelectric ceramic material (NKN-based) and is designed to operate efficiently at frequencies below 100 Hz. Experimental results show that the device can generate a power density of up to 22 μW/cm3 under an acceleration of 1 g at 20 Hz, which is highly competitive with existing energy harvesters. This work demonstrates the potential of using lead-free materials for sustainable energy harvesting technologies.
关键词： piezoelectric energy harvesting,NKN-based materials,low-frequency vibrations,lead-free ceramics,bimorph structure
更新于2025-09-23 15:22:29
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Efficient and stable emission of warm-white light from lead-free halide double perovskites
摘要： Lighting accounts for one-fifth of global electricity consumption1. Single materials with efficient and stable white-light emission are ideal for lighting applications, but photon emission covering the entire visible spectrum is difficult to achieve using a single material. Metal halide perovskites have outstanding emission properties2,3; however, the best-performing materials of this type contain lead and have unsatisfactory stability. Here we report a lead-free double perovskite that exhibits efficient and stable white-light emission via self-trapped excitons that originate from the Jahn–Teller distortion of the AgCl6 octahedron in the excited state. By alloying sodium cations into Cs2AgInCl6, we break the dark transition (the inversion-symmetry-induced parity-forbidden transition) by manipulating the parity of the wavefunction of the self-trapped exciton and reduce the electronic dimensionality of the semiconductor4. This leads to an increase in photoluminescence efficiency by three orders of magnitude compared to pure Cs2AgInCl6. The optimally alloyed Cs2(Ag0.60Na0.40)InCl6 with 0.04 per cent bismuth doping emits warm-white light with 86 ± 5 per cent quantum efficiency and works for over 1,000 hours. We anticipate that these results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes for next-generation lighting and display technologies.
关键词： lead-free halide double perovskites,self-trapped excitons,white-light emission,photoluminescence efficiency,Jahn–Teller distortion
更新于2025-09-23 15:21:21
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A thermodynamic potential for barium zirconate titanate solid solutions
摘要： Barium zirconate titanate [Ba(ZrxTi1?x)O3] solid solutions are promising lead-free ferroelectric materials that have received substantial interest. Thermodynamic analysis based on phenomenological Landau–Devonshire theory is a powerful method for theoretical investigation of ferroelectric materials, but cannot be applied to Ba(ZrxTi1?x)O3 because there is no thermodynamic potential. In this paper, a thermodynamic potential for Ba(ZrxTi1?x)O3 (0 ≤ x ≤ 0.3) solid solutions is constructed, and then a thermodynamic analysis carried out. The results accurately reproduce known phase structures and their transition temperatures, with good agreement with experimentally measured polarization, dielectric, and piezoelectric constants. It is found that Ba(ZrxTi1?x)O3 solid solutions at room temperature have three phase boundaries, including a tetragonal–orthorhombic phase boundary at x = 0.013, an orthorhombic–rhombohedral phase boundary at x = 0.0798, and a rhombohedral–paraelectric phase boundary at x = 0.2135. The results also indicate that the chemical composition-induced ferroelectric–paraelectric phase boundary has superior electromechanical properties, suggesting a new way to enhance electromechanical coupling in Ba(ZrxTi1?x)O3 solid solutions.
关键词： Landau–Devonshire theory,electromechanical properties,solid solutions,lead-free ferroelectric materials,Barium zirconate titanate,phase boundaries,thermodynamic potential
更新于2025-09-23 15:21:21
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Eco-friendly highly sensitive transducers based on a new KNN-NTK-FM lead-free piezoelectric ceramic for high-frequency biomedical ultrasonic imaging applications
摘要： High-frequency ultrasonic imaging with improved spatial resolution has gained increasing attention in the field of biomedical imaging. Sensitivity of transducers plays a pivotal role in determining ultrasonic image quality. Conventional ultrasonic transducers are mostly made from lead-based piezoelectric materials that may be harmful to the human body and the environment. In this study, a new (K,Na)NbO3-KTiNbO5-BaZrO3-Fe2O3-MgO (KNN-NTK-FM) lead-free piezoelectric ceramic was utilized in developing eco-friendly transducers for high-frequency biomedical ultrasonic imaging applications. A needle transducer with a small active aperture size of 0.45 × 0.55 mm2 was designed and evaluated. The transducer exhibits great performance with a high center frequency (52.6 MHz), a good electromechanical coupling (keff ~ 0.45), a large bandwidth (64.4% at -6 dB), and a very low two-way insertion loss (10.1 dB). Such high sensitivity is superior to those transducers based on other lead-free piezoelectric materials and can even be comparable to the lead-based ones. Imaging performance of the KNN-NTK-FM needle transducer was analyzed by imaging a wire phantom and an agar tissue-mimicking phantom. Imaging capabilities of the transducer were further demonstrated by ex vivo imaging studies on a porcine eyeball and a rabbit aorta. The results suggest that the KNN-NTK-FM piezoceramic has many attractive properties over other lead-free piezoelectric materials in developing eco-friendly highly sensitive transducers for high-frequency biomedical ultrasonic imaging applications.
关键词： lead-free piezoelectric ceramic,Biomedical ultrasonic imaging,high-frequency ultrasonic transducer,eco-friendly
更新于2025-09-23 15:21:21
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Direct ink writing macroporous lead-free piezoelectric Ba <sub/>0.85</sub> Ca <sub/>0.15</sub> Zr <sub/>0.1</sub> Ti <sub/>0.9</sub> O <sub/>3</sub>
摘要： Direct ink writing has become a widespread additive manufacturing technique for material engineering, but its application in lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) piezoelectric ceramics from aqueous systems has not been reported so far to our knowledge. The main obstacle is the high extent of hydrolysis reactions undergone by the starting powders when dispersed in water, hindering the attainment of stable water-based colloidal suspensions. This paper reports on the preparation of stable aqueous inks from a deagglomerated and surface treated powder synthesized by solid-state reaction and on direct ink writing of macroporous lead-free piezoelectrics. Based on zeta potential and rheological measurements, the optimal amounts of processing additives (dispersant, binder and coagulating agent) were selected to transform the initial fluid suspension to a viscoelastic paste with sufficient stiffness and stability for the printing process. Dielectric and piezoelectric properties of samples sintered under different temperatures were also investigated.
关键词： Direct ink writing,powder surface treating,lead-free piezoelectrics,viscoelasticity
更新于2025-09-23 15:21:21