Lead-free (Bi1/2Na1/2)TiO3 (BNT)-based incipient piezoelectrics are highly promising for high strain actuators, but the high electric fields (4 ~ 6 kV/mm) required for activation limit practical device integration. In the current literature, large strains are frequently attributed to local structural variations like microscopic core-shell architectures. This work systematically investigates an alternative pathway by introducing A-site Strontium (Sr) excess non-stoichiometry into 0.74(Bi1/2Na1/2)TiO3‒0.26SrTiO3 (BNST26) ceramics. Microstructural and X-ray diffraction analyses reveal highly dense, uniform matrices completely devoid of micro-scale core-shell boundaries or macroscopic symmetry distortions, revealing that Sr non-stoichiometry diverges from typical Bi-excess mechanisms. Interestingly, despite negligible variations in overall macro-scale strain behavior across the composition series, a peak normalized strain (Smax/Emax) of approximately 804 pm/V is achieved at a low driving field of 2 kV/mm for the 1 mol% Sr-excess specimen (x = 0.010). These results indicate that while Sr non-stoichiometry weakly influences nanoscale stability, it can be inferred that subtle modifications of local defect configurations optimize switching energy barriers, enabling high-strain, low-drive-field performance in lead-free relaxors.
In advanced device technologies such as microelectromechanical systems (MEMS), nanoscale electronics, optoelectronic components, and piezoelectric devices, the demand for enhanced mechanical, electrical, and optical performance together with high reliability continues to grow. In response, a variety of functional thin-film materials have been developed; among them, Pb(Zr,Ti)O₃ (PZT) thin films with high piezoelectric coefficients have emerged as key materials for realizing highperformance sensors and actuators. However, residual stress within thin films can adversely affect device reliability, performance, and lifetime. This tutorial paper provides a practical and step-by-step guide to residual stress analysis using X-ray diffraction (XRD) based on the sin²φ method. As a representative case study, we quantitatively analyze the in-plane residual stress of a PZT thin film deposited on a flexible metal-foil substrate. Residual stress was evaluated using X-ray diffraction (XRD) in combination with the sin²φ method. The present analysis is expected to deepen understanding of residual-stress behavior in thin films and to inform stress-aware design and reliability optimization of PZT-based devices
The growing demand for thinner, lighter, and more energy-efficient electronic systems has driven the development of acoustic technologies toward compact and flexible sound generation platforms. Despite significant progress, conventional electromagnetic speakers remain limited by bulky structures, energy losses, and poor compatibility with modern ultrathin devices. In this review, recent advancements in piezoelectric acoustic systems are presented, demonstrating a new generation of speakers capable of producing high-fidelity sound from ultra-slim, lightweight, and mechanically compliant designs. Through refined structural configurations and efficient electromechanical coupling, these piezoelectric exciters achieve strong acoustic output, fast response, and wide frequency operation while drastically reducing component thickness. These exciters also show their suitability for seamless integration into flexible displays, wearable devices, and automotive panels, offering enhanced spatial audio practicality and multifunctional operation, including demonstrative output and sensing. This advancement marks a step toward the convergence of acoustic, haptic, and interactive technologies, for the realization of sustainable and immersive humanmachine interfaces in future electronic and automotive systems.
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Flexible piezoelectric cross-bar array sensors for upper-limb kinesthetic sensing via muscle dynamics Junki Lee, Jihun Choi, Hyunseung Kim, Min Gon Son, Dong Yeol Hyeon, Jung Hwan Park, Andris Šutka, Chang Kyu Jeong Journal of the Korean Ceramic Society.2026;[Epub] CrossRef
Rietveld refinement has become an essential tool for the quantitative analysis of crystal structures in polycrystalline systems using X-ray diffraction data. This tutorial paper focuses on the background, case studies, and practical implementation of Rietveld refinement using the open-source software PROFEX. Key structural parameters, such as lattice constants and phase fractions, can be quantitatively extracted through full-pattern fitting. Case studies involving compositional variation, electric fields, temperature changes, and battery cycling demonstrate the broad applicability of Rietveld refinement in materials science, energy storage, and catalysis. A step-by-step procedure for performing Rietveld refinement is presented using Bi1/2Na1/2TiO3 perovskite ceramic as an example, providing guidance on software installation, preparing crystal structure information files, performing Rietveld refinement, evaluating results using R-factor and χ² values, and summarizing the results. This tutorial aims to improve understanding and accessibility of Rietveld refinement for researchers seeking to investigate structure-property relationships in complex material systems.
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Bandgap tuning in anion-mixed perovskite oxysulfide BaZrO3-xSx Munir Ahmad, Seongboo Park, Hwan Min Kim, Muhammad Sheeraz, Chang Won Ahn, Ill Won Kim, Soobeom Shin, Hu Young Jeong, Furqanul Hassan Naqvi, Jae-Hyeon Ko, Jieun Kim, Young-Han Shin, Tae Heon Kim Current Applied Physics.2026; 89: 100. CrossRef
NTC (negative temperature coefficient) thermistors are semiconductor ceramics whose resistance decreases with increasing temperature, making them essential components in various temperature sensing applications. Typically, ceramic materials are sintered at high temperatures exceeding 1,150°C. However, in laminated devices incorporating internal electrodes, co-sintering can lead to cracking and mechanical failure due to mismatches in the thermal expansion coefficients between the ceramic layers and metal-based electrodes. Moreover, the use of noble metal electrodes increases production costs. To address these challenges, a low-temperature sintering approach is required. Previous studies have demonstrated that incorporating glass frit can reduce the sintering temperature of ceramics, although this often results in increased electrical resistance. In this study, NiMnCoO₄ (NMC) ceramics, as a representative NTC thermistor composition, were prepared with the addition of 10 wt% glass frit. To mitigate the resulting increase in resistivity, trace amounts (1 wt%) of various metal oxides, including CuO, ZnO, and MnO, were introduced. Among these, the addition of CuO notably decreased both the resistivity and B constant values. In contrast, MnO had little effect on resistivity, while ZnO led to an increase. With respect to the B25/85 constant, samples containing MnO and ZnO exhibited higher values than those without metal oxide additives. These findings indicate that the incorporation of 1 wt% CuO is effective in reducing the increased resistivity in NMC ceramics subjected to low-temperature sintering via glass frit addition.
NTC thermistors are essential components widely used for temperature sensing in various electronic sensor applications. However, conventional NTC thermistor ceramics typically require high sintering temperatures above 1150℃, necessitating the use of high-cost noble metal electrodes such as palladium (Pd) or platinum (Pt), which increases the overall manufacturing cost. In this study, low-melting-point oxides were successfully introduced as sintering aids to reduce the sintering temperature of NiMnCoO₄-based semiconducting ceramics. As the additive content increased, the B constant and average grain size exhibited an increasing trend, while the sample containing 5 wt% additives showed the lowest room-temperature resistivity. Furthermore, samples sintered at 1000℃ demonstrated slightly higher room-temperature resistivity and B constant values compared to those sintered at 1150℃. These results confirm that the addition of low-melting-point oxides is effective in lowering the sintering temperature of NiMnCoO₄ ceramics, suggesting the potential for reducing production costs and improving design flexibility in thermistor fabrication.
Piezoelectric thin films have become increasingly significant in applications such as MEMS devices, wearable electronics, and lab-on-a-chip systems due to the miniaturization and integration of electronic devices. For piezoelectric thin films, even when an electric signal is applied in the thickness direction, greater deformation can often be observed in the in-plane direction, which is perpendicular to the electric field. Therefore, piezoelectric thin film devices are frequently designed using the transverse mode. As a result, it is crucial to evaluate piezoelectric thin films by measuring their transverse piezoelectric coefficient. This tutorial paper introduces a method for evaluating the effective transverse piezoelectric coefficient (e31,f) of piezoelectric thin films using laser Doppler vibrometry (LDV). Additionally, the paper outlines a step-by-step procedure for measuring e31,f while using Bi1/2Na1/2TiO3-based piezoelectric thin films as an example. This tutorial is expected to provide a practical and valuable method for measuring and analyzing the transverse piezoelectric properties, thereby supporting the development of new piezoelectric thin film materials.
Piezoelectric ceramics play an important role in various electronic applications. However, traditional ceramics are difficult to be used in some complicated structures, due to their low flexibility and high brittleness. To solve this problem, this study prepared and investigated ceramic/polymer composites that can utilize a good flexibility of polymers. Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and 0.77(Bi1/2Na1/2)TiO3-0.23SrTiO3 (BNST23) ceramics were selected to fabricate the composites. Ceramic/polymer composites were prepared using various volume fractions of BNST23 ceramics. The distribution of piezoceramic particles in BNST23/PVDF-TrFE composites was investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The dielectric and piezoelectric properties of the composites were significantly influenced by the volume fraction of the piezoelectric ceramics. As a result, the highest piezoelectric constant (d33) of 56 pC/N was obtained in a composites with 70% volume fraction of BNST23 ceramics. Accordingly, it is expected that BNST23/PVDF-TrFE composites can be applied to various sensor applications.
The measurement of strain under an electric field has been widely employed to comprehend the fundamental principles of electro-mechanical responses in ferroelectric, piezoelectric, and electrostrictive materials. In particular, understanding the strain properties of piezoelectric materials in response to electrical stimulation is crucial for researching and developing components such as piezoelectric actuators, acoustic devices, and ultrasonic generators. This tutorial paper introduces the components and operational principles of the linear variable differential transducer (LVDT), a widely used displacement measurement device in various industries. Additionally, we present the configuration of an experimental setup using LVDT to measure the strain characteristics of ferroelectric, piezoelectric, or electrostrictive materials under the application of an electric field. This paper includes simple measurement results and analyses obtained through the LVDT experimental setup, providing valuable information on research methods for the electro-mechanical interactions of various materials.
Piezoelectric ceramics play an important role in electrical and electronic devices such as sensors, actuators, and microelectronic devices. However, traditional ceramics are difficult to be used in various process industries due to their high brittleness and low flexibility. Therefore, piezoelectric paint sensors have been designed for application to the curved surfaces of complicated structures. Furthermore, recently, significant attention has been focused on the development of paint sensors that can be used as structure health monitoring sensors for vibration, impact, and acoustic emission. Several studies have successfully demonstrated the possibility that smart paint sensors can take the place of traditional ceramic sensors. In this review, we briefly introduce the concept of the piezoelectric paint sensors and the expected application field as well as their preparation and history.
It was reported that a tetragonal phase can be stabilized with maintaining good piezoelectric properties when Na0.5K0.5NbO3 (KNN) is modified with 0.06 mol SrTiO3. However, such a high amount of SrTiO3 leads not only to poor sinterability but low Curie temperature (TC). To maintain high TC with good piezoelectric properties in KNN-based lead-free piezoelectric ceramics, this study investigates the effect of Li-doping on the dielectric and piezoelectric properties of 0.96Na0.5K0.5NbO3-0.04SrTiO3 (KNN-4ST) ceramics. As a result, the orthorhombic-tetragonal phase transition was observed at 2 mol% Li2CO3 modified KNN-4ST ceramics, whose TC, d33 and kp values are 328℃, 165pC/N and 0.33, respectively.
This study investigated crystal structures, microstructures, and electric-field-induced strain (EFIS) properties of Bibased lead-free ferroelectric/relaxor composites. Bi1/2(Na0.82K0.18)1/2TiO3 (BNKT) as a ferroelectric material and 0.78Bi1/2(Na0.78K0.22)1/2TiO3-0.02LaFeO3 (BNKT2LF) as a relaxor material were synthesized using a conventional solid-state reaction method, and the resulting BNKT2LF powders were subjected to high-energy ball milling (HEBM) after calcination. As a result, HEBM proved a larger average grain size of sintered samples compared to conventional ball milling (CBM). In addition, the increased sintering time led to grain growth. Furthermore, HEBM treatment and sintering time demonstrated a significant effect on EFIS of BNKT/BNKT2LF composites. At 6 kV/mm, 0.35% of the maximum strain (Smax) was observed in the HEBM sample sintered for 12 h. The unipolar strain curves of CBM samples were almost linear, indicating almost no phase transitions, while HEBM samples displayed phase transitions at 5~6 kV/mm for all sintering time levels, showing the highest Smax/Emax value of 700 pm/V. These results indicated that HEBM treatment with a long sintering time might significantly enhance the electromechanical strain properties of BNT-based ceramics.
In functional materials, in situ experimental techniques as a function of external stimulus (e.g., electric field, magnetic field, light, etc.) or changes in ambient environments (e.g., temperature, humidity, pressure, etc.) are highly essential for analyzing how the physical properties of target materials are activated/evolved by the given stimulation. In particular, in situ electric-field-dependent X-ray diffraction (XRD) measurements have been extensively utilized for understanding the underlying mechanisms of the emerging electromechanical responses to external electric field in various ferroelectric, piezoelectric, and electrostrictive materials. This tutorial article briefly introduces basic principles/key concepts of in situ electric-field-dependent XRD analysis using a lab-scale XRD machine. We anticipate that the in situ XRD method provides a practical tool to systematically identify/monitor a structural modification of various electromechanical materials driven by applying an external electric field.
We investigated the microstructure, crystal structure, dielectric, and elecromechanical strain properties of lead-free BaTiO3 (BT)-modified (Bi1/2Na1/2)TiO3-SrTiO3 (BNT-ST) piezoelectric ceramics. Samples were prepared by a conventional ceramic processing route. Temperature dependent dielectric properties confirmed that a phase transition from a nonergodic relaxor to an ergodic relaxor was induced when the BT concentration reached 1.5 mol%, interestingly, where the average grain size reached a maximum value of 4.5 μm. At the same time, enhanced electromechanical strain (Smax/Emax = 600 pm/V) was obtained. It is suggested that the induced ferroelectric-relaxor phase transition by the BT modification is responsible for the enhancement of electromechanical strain in 1.5 mol% BT-modified BNT-ST ceramics.
For the last decades, a research hotspot for the halide perovskites (HPs) is now showing great progress in terms of improving efficiency for numerous photovoltaic devices (PVDs). However, it still faces challenges in the case of long-term stability in the air atmosphere. Defect-free high-quality HP single crystals show their promising properties for the remarkable development of highly efficient and stable PVDs. Here, we summarize the growth processing routes for the stable HP single crystals as well as briefly discuss the pros and cons of those well-established synthesis routes. Furthermore, we briefly include the comparison note between the HP single crystals and polycrystalline perovskite films regarding their device applications. Based on the future progress, the review concludes subjective perspectives and current challenges for the development of HPs high-quality PVDs.
This study investigated the low temperature sintering with various templates of Bi-based lead-free piezoelectric ceramics. The effects of using CuO-coated Na0.5Bi4.5Ti4O15 templates on the sintering behavior as well as the dielectric, ferroelectric, and piezoelectric properties of Bi1/2(Na0.78K0.22)1/2TiO3 (BNKT) ceramics have been examined. In comparison with the specimens sintered with the Na0.5Bi4.5Ti4O15 templates without CuO coating, those sintered with the CuO-coated Na0.5Bi4.5Ti4O15 templates showed larger template sizes as well as a larger electric field induced strain (Smax/Emax) of 422 pm/V after sintering at temperatures as low as 975℃. These results are promising for low-cost multilayer ceramic actuator applications.
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