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Abstract Ultrasound-driven bioelectronics could offer a wireless scheme with sustainable power supply; however, current ultrasound implantable systems present critical challenges in biocompatibility and harvesting performance related to lead/lead-free piezoelectric materials and devices. Here, we report a lead-free dual-frequency ultrasound implants for wireless, biphasic deep brain stimulation, which integrates two developed lead-free sandwich porous 1-3-type piezoelectric composite elements with enhanced harvesting performance in a flexible printed circuit board. The implant is ultrasonically powered through a portable external dual-frequency transducer and generates programmable biphasic stimulus pulses in clinically relevant frequencies. Furthermore, we demonstrate ultrasound-driven implants for long-term biosafety therapy in deep brain stimulation through an epileptic rodent model. With biocompatibility and improved electrical performance, the lead-free materials and devices presented here could provide a promising platform for developing implantable ultrasonic electronics in the future.

Abstract Dielectric capacitors with a fast charging/discharging rate, high power density, and long‐term stability are essential components in modern electrical devices. However, miniaturizing and integrating capacitors face a persistent challenge in improving their energy density (Wrec) to satisfy the specifications of advanced electronic systems and applications. In this work, leveraging phase‐field simulations, we judiciously designed a novel lead‐free relaxor ferroelectric material for enhanced energy storage performance, featuring flexible distributed weakly polar endotaxial nanostructures (ENs) embedded within a strongly polar fluctuation matrix. The matrix contributes to substantially enhanced polarization under an external electric field, and the randomly dispersed ENs effectively optimize breakdown phase proportion and provide a strong restoring force, which are advantageous in bolstering breakdown strength and minimizing hysteresis. Remarkably, this relaxor ferroelectric system incorporating ENs achieves an exceptionally high Wrec value of 10.3 J/cm3, accompanied by a large energy storage efficiency (η) of 85.4%. This work introduces a promising avenue for designing new relaxor materials capable of capacitive energy storage with exceptional performance characteristics.

Abstract Objective To understand the prevalence of hypertension and hyperlipidaemia as well as the current status of glycaemic control and its influencing factors among type 2 diabetes mellitus patients in the community in South China, and to provide recommendations for the prevention and control of diabetes. Methods Questionnaires, physical examinations and laboratory tests were conducted on patients with type 2 diabetes mellitus who participated in the National Basic Public Health Service Programme in Guangzhou in 2020. The chi-square test, t-test and multi-factor unconditional logistic regression analysis were performed using R 4.1.2 software. Result Among 127,423 type 2 diabetic patients in Guangzhou, 57,695 achieved glycemic control standards, with a glycemic control rate of 45.28%.In this study, the proportion of T2DM patients with hypertension and hyperlipidaemia together was 27.79%, The percentage of T2DM patients with hypertension alone and hyperlipidaemia alone was 28.34% and 20.53% respectively, and the rate of no complications was 23.34%. There was a statistically significant difference in the rate of glycaemic control between the different disease combination states (P

Large electrostrains with high temperature stability and low hysteresis are essential for applications in high-precision actuator devices. However, achieving simultaneously all three of the aforementioned features in ferroelectric ceramics remains a considerable challenge. In this work, we firstly report a high unipolar electrostrain (0.12% at 60 kV/cm) in (1–x)NaNbO3-x[(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3] (NN-xBCZT) ferroelectric polycrystalline ceramics with excellent thermal stability (variation less than 10% in the temperature range of 30–160 °C) and ultra-low hysteresis (

For relaxor ferroelectrics, correlating their properties and local structures is challenging. Here, the authors correlate the atomic-scale structure and the large dynamic electromechanical property in Bi0.5Na0.5TiO3-based relaxor ferroelectrics.

Bi0.5Na0.5TiO3 (BNT)-based ceramics are one of the most promising lead-free ferroelectrics due to their high strain property. Compared to other chemical modifications, rare earth ions doping provides significant possibility to optimize the strain property of BNT-based ceramics. In this work, the effects of rare earth ions on phase structure, microstructure, and strain & electrostrictive properties of lead-free BNT-based ceramics were systematically investigated. Rare earth ions (i.e., La3+, Sm3+, Yb3+, Dy3+, and Nd3+) were selected as the doping ions. Introducing moderate La3+ ions can drive the ferroelectric state of BNT-based ceramics to nonergodic relaxor state or ergodic relaxor state. The enhanced strain response of ∼0.40–0.42% and high converse piezoelectric coefficient of ∼600–630 pm/V can be achieved under 60–70 kV/cm for La3+-doped ceramic with nonergodic relaxor state. Besides, the giant electrostrictive coefficient Q33 of ∼0.047 m4/C2 can be obtained for La3+-doped ceramic with ergodic relaxor state. Other rare earth ions also present the promotion effect on strain enhancement for BNT-based ceramics. This study affords a significant guidance to optimize strain and electrostrictive properties of BNT-based ceramics via rare earth ions doping.

Simultaneous composition and valence-dependent strain regulation is achieved in lead-free (Bi0.5Na0.4K0.1)1-2xSm2xTi1-xMnxO3 (BNKT-SM100x) ceramics by a facile co-doping design with Sm3+ and Mn2+. By simply controlling the sintering temperature, Mn ions exhibited mixed-oxidation states with different ion radius and electronic structures, further adjusting the crystalline field. The regulated disorder degree finally induced large electro-strain (0.445%) under appropriate doping contents (x ​= ​0.01) and sintering temperature (1150 ​°C). Moreover, the random effect of Mn2+ (arising from the different valence and radius comparing with Ti4+) is stronger than the pinning effect due to the suppressed oxygen vacancies, and the different crystal structures may also affect the role of Mn2+. The domain morphologies with mixed nanodomain and ferroelectric domain were observed in the BNKT-SM1 ceramics, further demonstrating the coexistence of random effect and pinning effect. It is believed that the self-strain regulation phenomenon in this work may serve as an effective strategy for designing ferroelectrics with high strain performance.

Experimentally manipulating bubble domains remains elusive especially in the bulk form of ferroelectrics. Here, the authors achieve self-confined bubble domains with multiple polar topologies in bulk Bi0.5Na0.5TiO3 ferroelectrics, demonstrating reversible and donut-like domain morphology evolution.

Domain pattern is the carrier of electromechanical property. A novel domain pattern will open a gate for ferroelectric nanodevice. A distinctive topological domain pattern termed as hierarchical vortex (Hvo) has been found in polycrystalline ferroelectric based on the first-principles-based atomistic method. The Hvo pattern displays a unique structure, which is a flux-closing vortex encircle an anti-vortex or a vortex and anti-vortex pair (VA). Each Hvo structure could be regarded as a single vortex to forming a vortex–anti-vortex pair with anti-vortex or forming a vortex–vortex array with the vortex. The mechanism of HVo obtained in polycrystalline ferroelectric has been found that the grain boundary (GB) equals the domain wall when the first-order vortex is in the vortex. The HVo will open a new view of the domain topology pattern and its evolution.

Abstract Global environmental concerns on the toxicity of lead‐based piezoelectrics impel the great mass fervor on investigations of lead‐free alternatives. Barium titanate (BaTiO3, BT) ceramics, the first discovered perovskite ferroelectrics, were widely employed to fabricate dielectric capacitors from 1950s. Since a piezoelectric breakthrough was achieved via chemical modification, intensive researches have been performed embracing lead‐free BT‐based piezoelectrics and their extensional functionalities. In this review, we encompass the state‐of‐the‐art progress on chemical modification tuning phase structure toward advanced electrical properties in BT‐based ceramics. Generally, modulated regularity of cations substitution on phase transition is summarized and clarified. Then, we highlight the common methodologies of phase structure (phase boundary, relaxor phase, room‐temperature phase transition, etc.) design for optimizing piezoelectricity, electrostrictive strain, electrocaloric, dielectric energy storage or permittivity performances, and cover the noticeable developments and relevant physical mechanisms. Finally, perspectives and challenges on future research issues are featured. This review proposes to exert the significant guidance and service for material design of BT‐based and other lead‐free perovskite materials with superior functionalities.

The BiAlO3 (BA) and (Bi0.5Na0.5)ZrO3 (BNZ) are selected to form a solid solution with (K0.48Na0.52)NbO3 via traditional solid state technique to optimize the electrical performance and temperature stability of KNN-based lead-free ceramics, simultaneously. Here we show that doped BA has a great influence on phase structure, morphologies, and electrical properties. The XRD patterns and dielectric constant versus temperature curves reveal that an increase in the BA content results in a transform of phase structures from a coexistence state of rhombohedral, orthorhombic and tetragonal phases to pseudocubic phase. Owing to the construction of R-O-T phase boundary, optimized performances (TC ∼ 336 °C, d33 ∼ 306 pC/N, kp = 0.48) are obtained in 0.962(K0.48Na0.52)NbO3-0.003BiAlO3-0.035(Bi0.5Na0.5)ZrO3 (KNN-3) ceramics. Based on the sintered KNN-3 ceramic samples, high-frequency ultrasound imaging transducers are designed and fabricated, which exhibits a high center frequency of 24.5 MHz, a broad −6 dB bandwidth of 97% and a high-sensitivity. Finally, the imaging characteristic of the lead-free transducers is demonstrated via ex vivo imaging of biological tissue structure. As environment friendly materials, the excellent electrical and acoustic performance of developed KNN-based ceramics has great potential for practical applications.

In this work, the effects of rare earth (RE) dopants on the phase structure, microstructure, and electrical properties of lead-free bismuth sodium titanate (BNT)-based ceramics were studied. Rare earth elements (i.e., Sm, Gd, Ho, Pr, Y, and Yb) were selected as the dopants to replace the Bi site of Bi0.5(Na0.8K0.2)0.5TiO3 ceramics. It was found that the addition of moderate RE ions reduced the temperature of ferroelectric-relaxor transition (Tf-r) and the dielectric maximum at lower temperature, while the slight influence on the dielectric maximum at higher temperature and microstructure were observed. Hereby, the three-stage evolution of phase structure after introducing RE ions was confirmed. A high piezoelectric coefficient d33 of ∼190 pC/N was achieved due to the improved dielectric constant in the state with stable electric field-induced ferroelectric phase. The high strain property and converse piezoelectric coefficient d33∗ of ∼340 pm/V were obtained in the state with the coexistence of nonergodic and ergodic relaxor phases when Tf-r approached room temperature. The degenerated overall electromechanical properties exhibited in the state with complete ergodic relaxor phase. This study affords a significant guidance for optimizing the piezoelectricity of BNT-based ceramics utilizing rare earth dopants. Keywords: BNT-Based ceramics, Rare earth doping, Phase structure, Electrical properties

Here, we developed one kind of novel TiO2 ceramics with colossal dielectric constant by chemical modifications (Bi3+ and Sb5+), and discussed the physical origin for giant dielectric constant. Effects of Bi and/or Sb on their microstructure, dielectric properties as well as its frequency and temperature stability were studied in detail. It was found that their dielectric properties are strongly sensitive to (Bi,Sb) contents, and colossal dielectric permittivity (CP) (104∼105) together with low dielectric loss (∼5.7%) can be obtained in a wide composition range. In addition, all the ceramics possessed good frequency (102∼106 Hz) and temperature (−150–200 °C) stability of dielectric properties. In addition, the defects caused by the Bi volatilization may be the reason for higher dielectric properties of (Bi0.5Sb0.5)xTi1−xO2 ceramics with respect to (A0.5Sb0.5)xTi1−xO2 (A = In, Pr, Dy, Sm, Gd, Yb, Ga, Al, Fe or Sc). According to the results of complex impedance and XPS, the electron-pinned defect-dipoles may be suitable to explain the CP phenomenon, and oxygen vacancies-induced by Bi3+&Sb5+ substitution for Ti4+ should be responsible for conduction mechanism. We believe that this profound investigation can benefit the development of TiO2 ceramics as a CP material.

Potassium–sodium niobate (K,Na)NbO3/(KNN) lead-free ceramics have drawn vast amount of attention as one of the effective alternatives to lead-based ones. In recent years, the author’s group concentrated their work on KNN-based ceramics. This paper reviews the main obtained results in authors’ laboratory on how to enhance the piezoelectric properties of KNN-based ceramics, including the ions or compounds substitution, the constructing and types of phase boundaries near room temperature, the investigation of other tools (sintering aids, synthesis technique, poling conditions) on properties. All the published papers up to now show the developing higher performance with maintaining high Curie temperature of KNN-based ceramics which has great potential for the future and is the key to success for the field.

To investigate the leakage mechanisms in cation -substituted BiFeO3 (BFO) thin films, in Bi site or Fe site or both sites, Bi0.92La0.08FeO3, BiFe0.95Mn0.05O3, and Bi0.92La0.08Fe0.95Mn0.05O3 thin films were grown in situ by radio frequency magnetic sputtering on SrRuO3/SrTiO3(111) substrates, where the (111) orientation is established in all thin films. The variation in cation substitution results in different leakage behavior of BFO thin films. Space charge limited conduction and a grain boundary limited behavior are responsible for the leakage behavior of Bi0.92La0.08FeO3 and BiFe0.95Mn0.05O3 thin films in a low electric field region, respectively, while an interface-limited Fowler-Nordheim tunneling is involved in their leakage behavior in a high electric field region. In contrast, the leakage of Bi0.92La0.08Fe0.95Mn0.05O3 endures a transition from an Ohmic conduction to space charge limited conduction with increasing electric fields. The three thin films however show little temperature dependence of the leakage behavior in the temperature range investigated.