A clamping domain structure is proposed to improve the amount of non-180° domain switching in BaTiO₃ based piezoelectric ceramics. Experimental results show a large unipolar strain of 0.23% at 5 kV/mm in aged 0.5 mol. % Mn doped BaTiO₃ ceramics with clamping domain structures, and the normalized strain (d₃₃^*= S_max/E_max) reaches 600 pm/V at low electric fields of 2 or 3 kV/mm. In contrast, pure BaTiO₃ ceramics with clamping domain structures exhibit no clear polarization constriction or strain enhancement at 3 kV/mm. Electron paramagnetic resonance spectra verify the existence of titanium vacancies, Mn²⁺ and Mn⁴⁺, in 0.5 mol. % Mn doped BaTiO₃ ceramics. These results indicate that the enhanced strain effect can be attributed to the combined effect of the clamping domain structure and stabilization of defect dipoles. This method provides a general way to obtain large strain in ferroelectrics.

Background: In computer-aided medical diagnosis or prognosis, the automatic classification of heart valve diseases based on heart sound signals is of great importance since the heart sound signal contains a wealth of information that can reflect the heart status. Traditional binary classification algorithms (normal and abnormal) currently cannot comprehensively assess the heart valve diseases based on analyzing various heart sounds. The differences between heart sound signals are relatively subtle, but the reflected heart conditions differ significantly. Consequently, from a clinical point of view, it is of utmost importance to assist in the diagnosis of heart valve disease through the multiple classification of heart sound signals. Methods: We utilized a Transformer model for the multi-classification of heart sound signals. It has achieved results from four abnormal heart sound signals and the typical type. Results: According to 5-fold cross-validation strategy as well as 10-fold cross-validation strategy, e.g., in 5-fold cross-validation, the proposed method achieved a highest accuracy of 98.74% and a mean AUC of 0.99. Furthermore, the classification accuracy for Aortic Stenosis, Mitral Regurgitation, Mitral Stenosis, Mitral Valve Prolapse, and standard heart sound signals is 98.72%, 98.50%, 98.30%, 98.56%, and 99.61%, respectively. In 10-fold cross-validation, our model obtained the highest accuracy, sensitivity, specificity, precision, and F1 score all at 100%. Conclusion: The results indicate that the framework can precisely classify five classes of heart sound signals. Our method provides an effective tool for the ancillary detection of heart valve diseases in the clinical setting.

Owing to the high power density, excellent operational stability and fast charge/discharge rate, and environmental friendliness, the lead-free Na_0.5Bi_0.5TiO₃ (NBT)-based relaxor ferroelectrics exhibit great potential in pulsed power capacitors. Herein, novel lead-free (1−x)(0.7Na_0.5Bi_0.5TiO₃-0.3Sr_0.7Bi_0.2TiO₃)-xBi(Mg_0.5Zr_0.5)O₃ (NBT-SBT-xBMZ) relaxor ferroelectric ceramics were successfully fabricated using a solid-state reaction method and designed via compositional tailoring. The microstructure, dielectric properties, ferroelectric properties, and energy storage performance were investigated. The results indicate that appropriate Bi(Mg_0.5Zr_0.5)O₃ content can effectively enhance the relaxor ferroelectric characteristics and improve the dielectric breakdown strength by forming fine grain sizes and diminishing oxygen vacancy concentrations. Therefore, the optimal W_rec of 6.75 J/cm³ and a η of 79.44% were simultaneously obtained in NBT-SBT-0.15BMZ at 20 °C and 385 kV/cm. Meanwhile, thermal stability (20–180 °C) and frequency stability (1–200 Hz) associated with the ultrafast discharge time of ~49.1 ns were also procured in the same composition, providing a promising material system for applications in power pulse devices.

The electrostrain behavior through reversible domain switching in aged acceptor-doped ferroelectric ceramics has been widely investigated in the past decade. However, previous works were focused on unpoled ceramics, which could only utilize part of domains to exchange nonequal crystalline axis to generate strain under external electric field. In this paper, we proposed an effective method: (1) Initially, the acceptor-doped ceramics should be poled. (2) Then, the ceramics need to be aged for enough time. (3) Finally, the applied electric field should be perpendicular to the poling direction. Our method can utilize more domains to exchange nonequal crystalline axis to contribute to electrostrain in comparison with unpoled ceramics reported in the literature. According to our method, the unipolar electrostrain of 1.5 mol. % Fe-doped (Pb,Ba,Sr)(Zr,Ti)O₃ ceramics in this work could reach 0.33%, which was 3.75 times larger than that of unpoled one at 3.0 kV mm⁻¹. Meanwhile, the normalized strain d₃₃^* could reach nearly 1100 pm V⁻¹ which was one of the highest values reported in ferroelectric ceramics. Additionally, the ceramics displayed interesting double or slim P-E (polarization-electric field) hysteresis loops at various electric fields. Our work provides a general method via reversible domain switching in aged acceptor-doped ferroelectric ceramics to obtain large electrostrain for high-displacement actuator applications.

Negative environmental consequences of traditional cooling technologies have spurred the development of newly emerged green cooling devices rooting in electrocaloric effect (ECE). The relaxor ferroelectrics represented by BaZrTiO₃ ceramics are being actively explored as a promising candidate for constructing ECE cooling devices. However, the reported electrocaloric (EC) response of BaZrTiO₃ is still limited, particularly under low and moderate electric fields, which greatly inhibits its practical application. In this work, we propose an interfacial coupling modulation approach to enhance the EC response of BaZrTiO₃ by introducing composition homogeneous and composition gradient multilayered structures. A systematic work was performed to study the dielectric, ferroelectric, and EC performances of BaZrTiO₃ multilayered ceramics consisting of BaZr_0.20Ti_0.80O₃ and/or BaZr_0.17Ti_0.83O₃. It was found that the optimized BaZr_0.17Ti_0.83O₃/BaZr_0.20Ti_0.80O₃ bilayered films displayed the maximum EC response of 4.1 K under 10 MV m⁻¹ at ambient conditions, corresponding to a high level of the coefficient of performance up to 18.33. The results demonstrate the efficiency of interfacial coupling modulation in boosting the EC response of relaxor ferroelectric ceramics, opening up an avenue to explore advanced electrocaloric systems with a giant electrocaloric effect.