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Size effect is a fundamental phenomenon in ferroelectric materials and grain size dependence of the dielectric and piezoelectric properties of BaTiO3 (BTO) ceramics has been observed. However, the dependence of flexoelectric response on grain size has not been reported, thus far. In this work, BTO ceramics with grain sizes ranging from 0.59 to 8.90 μm were prepared by a two-step sintering method. We found that with increasing grain size, the flexoelectric coefficient of BTO ceramics increases from less than 20 μC/m (grain size 0.59–0.69 μm) to more than 300 μC/m (grain size 8.90 μm), but the grain size dependence of the flexoelectric response is different from that of the dielectric and piezoelectric properties. Observation by piezoresponse force microscopy reveals that the surface regions of BTO ceramics are spontaneously polarized. Strong inhomogeneous strain is measured by grazing incidence x-ray diffraction and the resultant flexoelectric effect is enough to polarize the surface regions. Fitting of the flexoelectric data indicates that the grain size effect of the flexoelectric response can be well explained by the polarized surface layer mechanism. [ABSTRACT FROM AUTHOR]

Glass is one of the most essential materials in various industrial fields. A representative application is as interposers in the semiconductor and display industries and microfluidic devices in the bio‐industry. Due to technological advancements, electric devices and various products are becoming lighter and smaller. Consequently, precision processing of the substrate is becoming increasingly important. One significant leading technology among these is through glass via (TGV) technology, which is attracting attention as a future alternative to through silicon via. In particular, TGV should be capable of microfabrication with a large aspect ratio and a consistent small hole size. TGV is typically fabricated using a wet etching process, so wet etching technology is a prominent focus in microfabrication. However, glass has isotropic properties, making achieving a high aspect ratio difficult. Traditionally, research on the wet etching method using hydrofluoric acid (HF) has been conducted. Nevertheless, HF etching has several disadvantages, including air pollution and human harm. Additional studies have been performed to address these issues. This review paper will cover the conventional HF‐based wet etching method and alternative HF etching processes (eco‐friendly materials). This technology would significantly help overcome the traditional problems associated with HF etching and fabricating precision‐processed glass in the semiconductor, display, and bio‐device industries. [ABSTRACT FROM AUTHOR]

The magnetoelectric (ME) response of laminated composites consisting of BaFe12O19 and Pb(Zr,Ti)O3 ceramics is systematically investigated. A butterfly-shaped curve of a magnetoelectric coefficient emerges in both three-layer and multilayer composites. We show that the appearance of a 7 ppm residual strain in the BaFe12O19 layer after magnetization is the main reason for this special curve. We also observe the self-biasing effect of the composites and a maximum ME response from 0.6 to 5 mV/(Oe cm) in laminated composites with magnetic and ferroelectric layers of different thicknesses that can be measured at a zero-bias magnetic field. The repeatable and stable maximum and minimum values of the magnetoelectric coefficient can be obtained under periodically applied biasing magnetic fields, which is important for a practical device application. An electric-field control of ferromagnetism, evidenced by a 17%–19% enhancement in the magnetization of the BaFe12O19 layer after Pb(Zr,Ti)O3 is polarized, is observed in the composites, implying potential applications in memory devices for the composites. Our work indicates that both magnetic field-controlled polarization and electric-field-controlled magnetization exist in BaFe12O19/Pb(Zr,Ti)O3 laminated composites. [ABSTRACT FROM AUTHOR]

Poly (vinylidene fluoride)- based polymers have a relatively large electrocaloric effect (ECE) but low thermal conductivity. In some studies, the ECE obtained from indirect measurement deviates substantially from direct measurement. In this work, the ECE was investigated in composites containing the ferroelectric poly (vinylidene fluoride-trifluoro ethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] terpolymer and Al2O3 fillers. The ECE of the composites was directly measured using an infrared thermograph and indirectly obtained utilizing the Maxwell relation. The temperature changes obtained by indirect and direct measurements agree reasonably well with each other. In direct measurement, we found the temperature increase is larger than the temperature decrease at a high field or in the composites with a high concentration of nanoparticles, which can be attributed to the Joule heating effect caused by increased conductivity and dielectric loss. In the extreme case, the Joule heating dominates the temperature change, and only the temperature increase can be observed. Moreover, the temperature change is increased by more than 38% in the composite with 1.5% Al2O3 fillers. One reason for the enhanced ECE is the increase of the polar phase in terpolymer after the addition of the nanoparticles. At the same time, the thermal conductivity of the composite film is also increased by 21% due to the high thermal conductivity of Al2O3. [ABSTRACT FROM AUTHOR]

The flexoelectric response of Na0.5Bi0.5TiO3-based and (Ba,Sr)TiO3 ferroelectric ceramics with sputtered or fired-on Ag, Au, and Ag/Pd electrodes was investigated. We found that for all the ceramics, the flexoelectric response of the same material is strongly dependent on the methods used to fabricate the electrodes. The samples with fired-on electrodes have a much smaller flexoelectric response than those with sputtered electrodes, and for a certain composition, the flexoelectric response can be reduced by more than 99%. The reduction of flexoelectric response is attributed to the suppression of the contribution from the spontaneously polarized surface layers on ferroelectric ceramics to the flexoelectric response. Three reasons were proposed for the suppression of the surface effect, namely, the diffusion of some substances in electrode pastes to the surface regions of ferroelectric ceramics, stress relief, and the generation of impurity phases caused by the evaporation of volatile element during the firing of electrode materials at a high temperature. We also found that the flexoelectric response can approach the theoretically predicated response after the surface effect is reduced by fabricating fired-on electrodes on ferroelectric ceramics. Our results indicate that the large flexoelectric response of ferroelectric ceramics is mainly from the polarized surface layers and the surface effect is the primary mechanism leading to the deviation of measured flexoelectric response from the intrinsic response in ferroelectric ceramics, which has been an unresolved issue in the flexoelectric research field. [ABSTRACT FROM AUTHOR]

The chemical reduction has often been exploited to improve the dielectric, piezoelectric, and flexoelectric response of the perovskite oxides. In this work, the effect of reduction on the dielectric properties of Na0.5Bi0.5TiO3-based ceramics was investigated in a broad temperature range from −130 to 175 °C. After the reduction of the ceramics, three dielectric anomalies were observed. The two dielectric anomalies at a low temperature exhibit a thermally activated dielectric relaxation characteristic with an activation energy of ∼0.3 eV. Evidence indicates that the two dielectric anomalies are related to the hopping of electrons between the defective lattice sites which has an interaction with the dipoles existing in the bulk and the region close to the ceramic surface, respectively. The third dielectric anomaly is observed around room temperature, and the frequency-independent dielectric constant and loss are greatly increased in the reduced ceramics. The origin of the dielectric anomaly is argued to be related to the interaction of water with the ceramic surface region. The reduction produces a large number of oxygen vacancies, facilitating the water adsorption on the surface of the reduced ceramics. The interaction greatly increases the migration and conduction of protons, generating a pronounced dielectric anomaly. We also show that the similar dielectric anomaly, though very weak, also appears in other unreduced perovskite-type oxides, indicating that the interaction of water with the surface is a common phenomenon in perovskite-type oxides. [ABSTRACT FROM AUTHOR]