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Phononic crystals (PCs) can modulate an incident acoustic wave to provide subwavelength microparticles with stable and flexible manipulation. However, fixed artificial structures of the PCs usually result in a steady acoustic field profile, thus limiting the dynamic manipulation of microparticles. This study proposes the construction of a phononic crystal plate (PCP) using a pair of periodic oppositely arranged gratings on a plate. Under the PCP's resonance frequency, a pair of nonleaky A0 mode traveling Lamb waves that intrinsically exist in a thin plate were excited and propagated. The pair of waves formed a highly localized standing Lamb wave field between the pair of periodic gratings. By adjusting the phase of the incident acoustic wave, the positions of pressure nodes of the PCP-induced standing Lamb wave were changed in a quantitatively tunable manner. Thus, polystyrene microparticles trapped and aligned at the pressure nodes via the acoustic radiation force could be moved to achieve the translation motion with a resolution of 2.2 μm, approximately 1/160 wavelength in water. The proposed methodology will lead to the fabrication of a disposable and easily operated tool for dynamically manipulating microparticles in subwavelength regions by engineering acoustic fields using acoustic metamaterials in microfluidic devices for cell sorting and drug delivery. [ABSTRACT FROM AUTHOR]

We present the acoustophoretic motion of microparticles simultaneously driven by the acoustic streaming induced drag force (ASF) and acoustic radiation force (ARF) on a phononic crystal plate (PCP). A much faster acoustophoresis can be achieved via a PCP than a traditional standing wave in bulk and surface acoustic wave devices. The mechanism is attributed to the significantly enhanced ASF and ARF originating from the resonant excitation of a nonleaky zero-order antisymmetric Lamb mode intrinsically in the plate, which generates the highly localized field vertical to the surface and periodic field parallel to the surface. We also demonstrate the transition from the ASF dominated acoustophoresis to ARF dominated acoustophoresis as a function of particle size. The predicted trajectories and velocity of acoustophoretic particles by the proposed finite element model are in reasonable agreement with experimental phenomena. This study would aid the development of simple, scalable, integrated, and disposable phononic crystal based acoustofluidic systems for biomedical applications such as rapid mixing, cell trapping, sorting, and patterning. [ABSTRACT FROM AUTHOR]

Efficient and controllable gene/drug delivery triggered by sonoporation is critical to cellular therapy. This study reports on repairable sonoporation for massive cells trapped on a phononic crystal plate (PCP). This mechanism is generated by the effects of enhanced near-boundary streaming around the manipulated cells. The streaming is achieved by significantly improving the tangential acoustic field gradient along the cell boundary through resonant PCP excitation of the nonleaky Lamb modes intrinsically existing in the uniform plate. This structured field-induced repairable sonoporation may constitute an effective tool for drug delivery and gene transfection. [ABSTRACT FROM AUTHOR]

Over the past decades, lead-based relaxor ferroelectrics have served as the model systems to unravel the relationship between electromechanical properties and local structure. Here, by employing pair distribution function analysis and the reverse Monte Carlo method, we investigate the local structural features and their temperature dependence in relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-xPbTiO3 with x = 0.15 (PZN-15PT), which has a tetragonal average structure, but displays frequency dependence at low temperatures. The refined atomic model suggests that ordered polar nanoregions (PNRs) originate from the strong atomic displacive correlation, and their polar directions are the same as the crystallographic symmetry axis. The dipoles in the disordered matrix have weak correlations and can be averaged into a global tetragonal symmetry. These findings establish a detailed picture of the local structure of lead-based relaxor ferroelectrics and provide a deeper insight into the nature of PNRs. [ABSTRACT FROM AUTHOR]

AgNbO3 (ANO)-based lead-free antiferroelectric ceramics with high energy storage density show potential application in pulsed power systems. Structural heterogeneity via doping different ions offers an effective route to explore high performance dielectric materials. The effect of A-site and B-site modified ANO-based ceramics at the same doping amount of 50% on ferroelectricity was investigated. The result shows that the A/B site structural heterogeneities both improved relaxor features, which make a great contribution to the energy storage efficiency, while the B-site modification shows a more effective influence on the structure, grain growth, and ferroelectricity regulation. In this case, the optimized recoverable energy storage density of 2.6 J/cc with an improved efficiency of 87.6% was achieved in the Ta-ANO component. [ABSTRACT FROM AUTHOR]

By adopting an up-ramp density profile, we propose to generate relativistic electron mirrors from laser-driven underdense plasma waves, which are insensitive to finite thermal temperature within a certain range. Along the density ramp, premature wavebreaking due to thermal effects is shown to be well mitigated. Under sufficiently high amplitudes of wake excitation, overcritical dense electron mirrors can pile up when approaching the end of the up-ramp. The consequent mirror speed can be stably driven to the group velocity of the laser propagating in a corresponding uniform plasma. Compared with using purely uniform but thermal plasmas, the present thermal-insensitive mirrors can provide enhanced scattering efficiency and spectral upshift for a counter-propagating probe pulse. These observations are confirmed by multi-dimensional particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

The shear piezoelectric behavior of [001] poled tetragonal and [011] poled rhombohedral Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) crystals, with '1T' and '2R' domain configurations, respectively, were investigated under uniaxial stress perpendicular to polar direction. The shear piezoelectric coefficient d15 was found to decrease with increasing compressive stress for both '1T' and '2R' crystals. Based on thermodynamic analysis, the phase structure can be stabilized by applying compressive stress perpendicular to polar direction, resulting in a 'harder' polarization rotation process, accounts for the reduced shear piezoelectric coefficient. Of particular importance is that the allowable drive electric field was greatly increased and transverse dielectric loss was drastically reduced under compressive stress, leading to the improved maximum-shear-strain. [ABSTRACT FROM AUTHOR]

Texture engineering offers an approach for achieving enhanced properties in bulk ceramics by introducing crystallographic anisotropy. Recent developments on texture engineering have enabled the fabrication of highly aligned ferroelectric ceramics with single-crystal-like electromechanical properties. In this paper, we review the history and recent progress of texture-engineered ferroelectric ceramics. We expect that more explorations on template-related issues, including orientation mismatch, physical models of the textured grain growth, and micromorphology–property relationship, will advance the development of texture-engineered ferroelectric ceramics with further improved properties. [ABSTRACT FROM AUTHOR]

The temperature dependence of the shear piezoelectric responses in relaxor-PbTiO3 based perovskite crystals with rhombohedral, orthorhombic, and tetragonal phases were investigated. Based on thermodynamic analysis, high shear piezoelectric coefficients (d24) and good thermal stability were predicted in orthorhombic crystals, owing to the 'vertical' orthorhombic-rhombohedral phase boundary. By resonance measurements, shear piezoelectric coefficient d24 was found to be on the order of ∼2100 pC/N at room temperature, maintaining same value over the temperature range of -50-100 °C. In contrast, the shear piezoelectric coefficients d15, with values of 3300, 3600, and 2000 pC/N at room temperature for rhombohedral, orthorhombic, and tetragonal crystals, respectively, exhibited strong temperature dependent behavior due to their respective ferroelectric-ferroelectric phase transitions. [ABSTRACT FROM AUTHOR]

The piezoelectric properties of Pb(In0.5Nb0.5)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals with various engineered domain configurations were investigated. Rhombohedral and monoclinic/orthorhombic crystals poled along their crystallographic [011] directions were found to possess macroscopic mm2 symmetry, with '2R' and '1O' domain, respectively. Crystals with the '2R' domain configuration were found to exhibit high extensional piezoelectric coefficients d33 (∼1300 pC/N) and d32 (∼-1680 pC/N), while crystals with the '1O' configuration possessed high shear coefficients d15 (∼3500 pC/N) and d24 (∼2070 pC/N), with relatively low extensional piezoelectric coefficients d33 (∼340 pC/N) and d32 (∼-260 pC/N). The observed results were explained by 'polarization rotation' model, as related to their respective domain configurations. [ABSTRACT FROM AUTHOR]

Flexoelectricity yields electric polarization through graded strains and exists in various kinds of solid dielectrics but usually with a weak coupling response. In this letter, several Bi-doped Pb(Mg2/3Nb1/3)O3-xPbTiO3 (PMN-xPT) ferroelectric ceramics were prepared and the interplay of their piezoelectricity and flexoelectricity was systematically investigated. The largest flexoelectric response (∼300 μC/m) was 30 times larger than that of pure PMN-PT and was observed in the Bi-doped PMN-32PT, where the after poling piezoelectric coefficients were also the largest (990 pC/N) among all the compositions. This suggests that the apparent flexoelectricity in ferroelectrics is highly related to the bulk piezoelectricity. Therefore, introducing a local structural heterogeneity is considered as a feasible approach to achieve an ultrahigh piezoelectric response while also providing an ultrahigh flexoelectricity. [ABSTRACT FROM AUTHOR]

Pb-based relaxor piezoelectric single crystal composites (PSCCs) have attracted widespread attention for improving the bandwidth and sensitivity performance of acoustic transducers due to their excellent electromechanical and piezoelectric properties. Alternating current polarization (ACP) has been proven as an effective method for enhancing the dielectric and piezoelectric properties of relaxor-PbTiO3 single crystals. Herein, we investigated the effects of the amplitude, frequency, and cycle number of the poling electric field on the piezoelectric and dielectric performances of PSCCs and obtained the optimum poling condition of ACP. Compared with the traditional direct current poling method, both the dielectric permittivity ( ε 33 T / ε 0 ) and piezoelectric coefficient ( d 33 ) of the AC-poled PSCCs were both increased by up to 20%. Notably, the ACP PSCC with a volume fraction of 60% exhibited a high d 33 of 1610 pC/N, which is superior to values previously reported for PSCCs. This work provides an alternative strategy for enhancing the properties of PSCCs and may contribute to the further development of piezoelectric applications. [ABSTRACT FROM AUTHOR]

High-temperature piezoelectric devices require piezoelectric ceramics with high Curie temperatures and high-temperature stability of piezoelectric properties to avoid the depolarization of piezoelectric ceramics during application. However, piezoelectric materials with high Curie temperatures usually have restrained piezoelectric properties. Crystallographic orientation via texture engineering is a practicable way to improve piezoelectric performance. Here, we propose a sintering-aid-assisted template grain growth strategy to texture BiScO3-PbTiO3 ceramics to overcome the low orientation issue that challenges the texturing of BS-PT for decades. By judiciously selecting B2O3-CuO as sintering aids, we fabricated highly ⟨001⟩-textured 0.43BS-0.57PT ceramics with Logtering factors >99.0% that possess high piezoelectric coefficients d33 of 474–612 pC/N while maintaining relatively high Curie temperatures of 370–402 °C. Importantly, this work addresses a long-standing issue presented in BS-PT ceramics, i.e., the low electromechanical coupling property of BS-PT ceramics (k33 < 0.70) by improving the electromechanical coupling factor k33 to 81.2%. The newly designed textured BS-PT ceramics are thought to be promising candidates for the design of high-temperature piezoelectric transducers and actuators. [ABSTRACT FROM AUTHOR]

Various wireless sensors in the Internet of Things (IoT) systems have been adopted in ocean exploration, with increasing energy supply concern. Regarding the marine environment, self-powered sensors utilizing ambient flow and wave energy can increase maintainability with a long lifespan. However, the current underwater piezoelectric energy harvesters made of piezoelectric ceramics suffer from low power density (<0.5 mW cm−3 m−1 s). In this paper, we proposed a vortex-induction underwater piezoelectric energy harvester based on a Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystal macro-fiber composite (MFC). The single crystal MFC shows mechanical flexibility in which the volume fraction of the piezoelectric phase is 70%. Regarding the structure design, a bicylinder configuration with a ladder-shaped cantilever is employed for decreasing the resonant frequency of the underwater piezoelectric energy harvester and enhancing vortex force during fluid–structure interaction process. The designed underwater energy harvester exhibits a high output voltage of 54 Vpp at 0.9 m/s flow in the designed underwater energy harvesting test platform. Due to the high figure-of-merit d 32 × g 32 (7.65 × 10−11 m2/N) of the single crystal, the maximum output power reaches 62 μW under the flow speed of 0.9 m/s. The normalized power density is 1.1 mW cm−3 m−1 s, being 2.3 times larger than that of the state-of-the-art PZT ceramics-based underwater energy harvester. This work will help to mitigate the energy crisis of the IoT system, promoting the development of underwater equipment. [ABSTRACT FROM AUTHOR]

Flexoelectricity of semiconductors usually exhibits large flexoelectric coefficients due to their significantly enhanced surface piezoelectricity caused by surface symmetry breaking. In this Letter, we reported a general paradigm to tune the semiconductor flexoelectricity through interface engineering. We selected Nb-SrTiO3 (Nb-STO) single crystals as the targets and tuned their surface piezoelectricity through depositing TiO2-terminated and SrO-terminated ultra-thin BaTiO3 (BTO) films. The results suggested that the deposition of TiO2-terminated and SrO-terminated ultra-thin BaTiO3 films to Nb-STO can induce a downward and upward out-of-plane surface polarization, respectively, thereby significantly increasing/decreasing the apparent flexoelectric coefficients of Nb-STO single crystals. Our work proves the feasibility of interface engineering in the application of flexoelectricity and also provides a possible route to achieve the large apparent flexoelectricity of semiconductor materials. [ABSTRACT FROM AUTHOR]

The electrostrictive effect was investigated in Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) relaxor ferroelectric crystal, a representative high performance piezoelectric material, with respect to orientation, temperature, and composition. The electrostrictive coefficients Q11C, Q12C, and Q44C of PMN-xPT (x = 0.25-0.37) crystals were found to be on the order of 0.055, -0.024, and 0.020 m4/C2, respectively. The maximum and minimum Q33* were found to be along <100> and <111> directions, being about 0.055 and 0.014 m4/C2, respectively, showing a strong anisotropic behavior, which is inherently associated with the oxygen-octahedra structure. In contrast to piezoelectric and dielectric responses, the electrostrictive coefficients Q are found to be insensitive to the ferroelectric phase transition, no matter it is induced by the temperature or composition. [ABSTRACT FROM AUTHOR]

Traditional piezoelectric adaptive lenses (ALENS) are fabricated by piezoceramics with transparent liquids as the filling media. However, it is challenging to achieve high focal sensitivity and long-time robustness because of the low piezoelectricity of ceramics as well as the evaporation and leakage of the liquids. To overcome the above-mentioned issues, we design a piezoelectric lens based on a radial extension-arching mode by using polydimethylsiloxane films and Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIMNT) relaxor ferroelectric single crystals to replace the transparent liquids and Pb(Zr, Ti)O3 (PZT) ceramics, respectively. Due to the ultrahigh piezoelectric properties (d33 ∼ 1500 pC N−1 and d31 ∼ 730 pC N−1) of the PIMNT crystals and the optimized radial extension-arching structure, an ultrahigh focal sensitivity (8.5 cm V−1 and a fast response time (∼102μs) is achieved, outperforming conventional ALENS based on piezoceramic actuators (∼103 μs and ∼10−1 cm V−1) and dielectric elastomer actuators (∼105 μs and ∼10−2 cm V−1). The largest output displacement of our designed ALENS is up to 53.6 μm at 4.2 kHz under 80 Vpp, and its focus is in the range of 57.44 cm to ∞. Furthermore, its performance remains unchanged after 4 × 107 vibration cycles, indicating its long-time robustness. This work sheds light on the design of advanced adaptive optical systems, where an ultrahigh focal sensitivity and a fast response are required. [ABSTRACT FROM AUTHOR]

In this work, the piezoelectric unimorph of a Pb(In1/2Nb1/2)O3 -Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal by alternating current poling (ACP) was studied for vibration energy harvesting. The figure of merit of d 31 × g 31 of the 0.25PIN-0.43PMN-0.32PT single crystal was enhanced to be 29.3 × 10−12 m2/N by ACP, which is 1.9 times and 8.9 times as much as that of the 0.25PIN-0.43PMN-0.32PT single crystal and the commercial PZT5H ceramic by direct current poling (DCP), respectively. The piezoelectric unimorph of the 0.25PIN-0.43PMN-0.32PT single crystal by ACP produced the open circuit voltage of 67 Vp and the maximum power of 0.74 mW under on-resonance condition, which were 1.5 times and 1.8 times as much as the 0.25PIN-0.43PMN-0.32PT single crystal unimorph by DCP. Moreover, these were almost 2.4 times more voltage and 5.7 times more power than the PZT5H ceramic unimorph. Even under the off resonance condition, the piezoelectric unimorph of the 0.25PIN-0.43PMN-0.32PT single crystal by DCP and ACP produced 4.4 times and 8.0 times maximum output power as much as the PZT5H ceramic unimorph. ACP is a potential way to further enhance the output voltage and power of the 0.25PIN-0.43PMN-0.32PT single crystal unimorph for energy harvesting. [ABSTRACT FROM AUTHOR]

Low driving voltage is important for miniaturization and untethered service of millirobots made of piezoelectric materials. In this research, we designed a bio-inspired bimorph-structured millirobot with a transparent relaxor ferroelectric crystal. Due to the ultrahigh piezoelectricity of the relaxor ferroelectric crystals and the optimized bimorph-based structure, the millirobot shows a maximum moving speed up to 9.22 b s−1 (body length per second) at 100 V, while the minimum driving voltage for initial movement can be as low as 3 V, which is more than two orders of magnitude smaller than that of millirobot based on dielectric elastomers. The maximum and minimum power consumptions of the millirobot are 71.6 mW and 85.9 μW, respectively. The robustness of the millirobot is reflected in its mechanical load stability carrying a 78 g mass (97.5 times of its weight) and its cryogenic tolerance. This work is believed to be beneficial to the design of various robust electromechanical devices with low driving voltage. [ABSTRACT FROM AUTHOR]

Perovskite SnTiO3 (SNO) was predicted to be ferroelectric with a large spontaneous polarization. However, the perovskite phase SNO was found to be metastable in experiments. Here, we show that SNO perovskite phase can be stabilized by the interfacial geometry in ATiO3/SNO superlattices (A = Ca, Sr, Ba) of short periodicity using first principles calculations. We found that CaTiO3/SNO superlattice has the largest polarization. In all the superlattices investigated, a phase transition from tetragonal to monoclinic structure was found with increasing in-plane lattice constants. Accompanying this phase transition, polarization directions rotate from [001] to [110], which is promising for achieving large piezoelectric responses. [ABSTRACT FROM AUTHOR]

Coexisting micro-/nanostructures on a stretchable substrate offer localized functionality with programmability and dynamic regulation. Yet, the combination of different fabrication techniques is challenging. In this paper, a one-step methodology for such a surface is proposed by harnessing wrinkle instability at the targeted area with selected mechanical constraint during soft lithography. Partly covered by patterned constraints, a surface with nanostructures that replicate a template is obtained while the unconstraint part wrinkles as a result of classical morphology instability. The effect of constraints is investigated experimentally to guide the generation of two optical performances, chemical color and structural color, at the coexisting surface structures. A camouflage demonstration is illustrated, utilizing the strict consequence of wrinkle-flattening and structural color redshift upon stretching. [ABSTRACT FROM AUTHOR]

Strain behavior and piezoelectric properties of relaxor-PbTiO3 based crystals have been studied under the combination of electric field and static uniaxial transverse compressive stress. The transverse piezoelectric coefficient, d32, for crystals well into the rhombohedral phase was found to increase with increasing stress due to a morphotropic phase boundary (MPB) effect, while the values for crystals with MPB composition exhibit a contrary trend that is associated with the phase transformation. In addition, an ac drive field was found to depolarize the crystals under stress. Of particular significance is that manganese-modified crystals show stable piezoelectric properties under ac drive field and stress, which has potential for transducer applications. [ABSTRACT FROM AUTHOR]

Two-dimensional ultrawide bandgap materials have compelling potential advantages in nano high-power semiconductors, deep-ultraviolet optoelectronics, and so on. Recently, two-dimensional few-layer h-BeO predicted as an ultrawide bandgap material has been synthesized in the experiment. In the present work, the first-principles calculations show that monolayer h-BeO has an indirect bandgap of 7.05 eV with the HSE functional. The ultrawide bandgap results from the atomic electronegativity difference in the polar h-BeO. The electronic transport properties are also systematically investigated by using the Boltzmann transport theory. The polar LO phonons generate the macroscopic polarization field and strongly couple to electrons by the Fröhlich interaction. Limited by the electron-phonon scattering, monolayer h-BeO has a high mobility of 452 cm2 V−1 s−1 at room temperature. Further studies indicate that the biaxial tensile strain can reduce the electron effective mass and enhance the electron-phonon coupling strength. A suitable strain promotes the mobility to ∼1000 cm2 V−1 s−1 at room temperature. [ABSTRACT FROM AUTHOR]

Acoustic tweezers based on the focused field hold the promise of contactless manipulation of microparticles. However, acoustic diffraction severely limits the trapping strength and the minimum size of the trapped particles in conventional diffraction-limited systems. Here, we propose and demonstrate a simple cylindrical shell structure for the trapping of microparticles with a radius as small as 1/400 of the corresponding acoustic wavelength, and its trapping ability is much stronger than that of the standing wave. This mechanism is attributed to the significantly enhanced acoustic radiation force originating from the resonant excitation of low order circumferential modes intrinsically existing in the cylindrical shell, which is a highly localized field around its surfaces. Cylindrical shell-based acoustic tweezers are simple, disposable, low cost, biocompatible, and functional, which may be of interest for nano-scale manufacturing and biomedical applications such as bio-printing, cell culturing, and tissue engineering. [ABSTRACT FROM AUTHOR]

Acoustic tweezers hold great promise for potential applications in cell sorting due to their noncontact, noninvasive, and simple characteristics. Acoustic tweezers, however, have difficulty in separating the cells of the same size distribution, which hampers their applications. In this paper, we demonstrate that assisted by the targeted microbubble, two kinds of cells with an overlap in size distribution can be efficiently separated by surface acoustic waves. By specifically adhering the targeted microbubbles to MDA-MB-231 cells, the acoustic sensitivity of cells can be improved significantly, leading to the isolation of MDA-MB-231 from MCF-7 cells with an efficiency of 91.2 ± 3.4%. This method extends the diversity of acoustic separation and is capable of separation of particles with the same density and diameter, proving a strategy for specific cell sorting. [ABSTRACT FROM AUTHOR]

In this letter, we report on significant flexoelectric fatigue in lead-free (K,Na,Li)(Nb,Sb)O3 (KNNLS) ceramics. In the ferroelectric phase of KNNLS, the observed effective transverse flexoelectric coefficient, which is initially as high as 1 μC/m, decreases nonlinearly with increasing cycles of strain gradient, and the fatigue regulation is well reproduced by a stretched exponential function. By comparing the time dependence of dielectric permittivity and ferroelectricity in KNNLS ceramics, we conclude that large flexoelectric and flexocoupling coefficients in the ferroelectric phase originate mainly from ferroelectricity and that the related flexoelectric fatigue is likely due to the pinning effect of ferroelectric domains. [ABSTRACT FROM AUTHOR]