Electromechanical Applications Research Articles

Effect of Rheological on the Physical and Electrical Properties of Extruded Micro Carbon -LLDPE Composites

This study focuses on formulating and optimizing a conductive polymer composite (CPC) material tailored for electromechanical applications. Linear Low-Density Polyethylene (LLDPE) polymer and micro carbon particles derived from rice husk were compounded using a hot compaction process and melt blended through a single-screw extrusion machine. A mix of 50% loading of microcarbon particles was used in this research. It was determined that the experiment was successfully conducted, resulting in a stabilized density of approximately 1 g/cm³. The research demonstrates how the prototype Extruder Head effectively stabilizes the density of composites. Electrical conductivity demonstrated a notable increase in conductivity toward higher density. These findings underscore the successful development of a CPC material with improved electrical conductivity, making it a highly suitable tool for high carbon-loading composite material.

Time-dependent relaxation dynamics of remanent strain in textured PMN–PZ–PT and PMN–PIN–PT piezoceramics

Crystallographically textured lead-based piezoceramics, particularly Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 (PMN–PZ–PT) and Pb(Mg1/3Nb2/3)O3–Pb(In1/2Nb1/2)O3–PbTiO3 (PMN–PIN–PT), play a pivotal role in electromechanical applications due to their enhanced field-induced strain responses. However, challenges in precision positioning arise from heightened remanent strain (Sr) caused by embedded templates in the textured grains, impacting strain cycle consistency due to increased time delay for Sr relaxation. This study investigates the time-dependent relaxation dynamics of Sr in textured PMN–PZ–PT and PMN–PIN–PT piezoceramics, focusing on experimentally determining relaxation time between cycles required for complete Sr relaxation. Our findings reveal that the relaxation time in textured piezoceramics is notably longer than that in their non-textured counterparts, primarily due to pinning of domain walls by embedded templates. This work provides insights into the strain relaxation characteristics of piezoceramics and underscores the importance of time delay in designing precision positioning systems for improved reliability.

Local defect structure design enhanced energy storage performance in lead-free antiferroelectric ceramics

Antiferroelectrics (AFEs) are ideal candidates in dielectric, electromechanical, and electrothermal applications. NaNbO3 (NN), as a lead-free antiferroelectric (AFE) material under extensive investigation, exhibits ferroelectric (FE)-like polarization–electric field (P-E) hysteresis loops, characterized by high remnant polarization and large hysteresis. Herein, the local defect structure design is proposed to achieve high energy storage (ES) density in NN-based AFE ceramics. The pinning effect of defect dipoles and the enhancement of local structural disorder stabilize the AFE phase and reduce hysteresis losses. Consequently, an excellent ES performance of large recoverable energy density (Wrec) of 9.70 J/cm3 and high efficiency (η) of 88.75 % is concurrently obtained in NN-based relaxor AFE ceramics, with outstanding charge–discharge performance (PD∼413.2 MW/cm3, WD∼4.47 J/cm3), which are significantly improved compared to other reported values in lead-free ES ceramics. This indicates that NN-based ceramics are candidates for advanced ES capacitors and provides a feasible modulation approach for the development of new lead-free high-performance dielectric materials.

Revealing the mechanism of the electron-transfer induced and enhanced intrinsic auxeticity in 2D penta-materials

The intrinsic auxeticity of materials has long been attributed to their unique geometric configurations. Triggering and enhancing auxeticity presents significant challenges, as many nanomaterials display subtle auxetic effects with a negative Poisson's ratio (NPR) typically above -0.4. This paper introduces three materials with identical symmetry—two-dimensional pentagonal structures Penta-B2×2Y2 (i.e., Penta-B2C4, Penta-B2N4, and JP-B2C2N2)—to investigate a novel mechanism influencing material auxeticity: electron transfer. Specifically, variations in electron transfer cause Penta-B2N4 and JP-B2C2N2 to show axial auxetic effects, whereas Penta-B2C4 demonstrates opposite behavior. The axial NPR of Penta-B2N4 is ∼ -0.05, while for JP-B2C2N2, it reaches ∼-0.46, significantly surpassing that of typical intrinsic auxetic materials. This represents an increase of approximately 920 % compared to Penta-B2N4. Additionally, JP-B2C2N2 features semi-metallic properties, where the conduction band minimum (CBM) and the valence band maximum (VBM) are tangent to the Fermi level. Consequently, minor alterations in external conditions can induce a transition between semiconductor and metallic states in JP-B2C2N2. Thus, the 2D material JP-B2C2N2 emerges as a promising candidate for nanoelectronic and electromechanical applications. Furthermore, this study also enhances the academic understanding of auxetic properties in nanomaterials by linking their mechanical and electronic characteristics and laying a theoretical foundation for further experimental exploration of auxeticity.

Silicone elastomer dielectric composites by introducing novel O-MMT@TiO2 nanoparticles for energy harvesting application

Dielectric elastomers have attracted attention in emerging advanced electromechanical applications. However, how to simultaneously improve the dielectric constant and the breakdown strength of dielectric composite needs to be solved. In this paper, we propose a new strategy to anchor TiO2 nanoparticles onto organically modified montmorillonite (O-MMT) nanoplatelets through dehydration reaction to synthesize a novel filler O-MMT@TiO2. Then, the O-MMT@TiO2 is incorporated into methyl vinyl silicone rubber (MVSR) matrix to obtain O-MMT@TiO2/MVSR dielectric composites. Comparing with the composites by direct mixing of TiO2 and O-MMT in MVSR (O-MMT/TiO2/MVSR), O-MMT@TiO2/MVSR composites significantly increase mechanical and dielectric and energy storage properties. 30 wt% O-MMT@TiO2/MVSR composite achieves the highest energy storage density of 118.65 kJ/m3, which is 142.9 % higher than that of 15 wt%O-MMT/15 wt%TiO2/MVSR (48.84 kJ/m3). This study offers an effective method for the preparation of high-performance dielectric elastomer materials, which can be exploited for the energy harvesting application.

A novel 3D mixed finite element for flexoelectricity in piezoelectric materials

AbstractFlexoelectricity is the intrinsic length‐scale dependent higher‐order electromechanical response of all centro‐ and non‐centro‐symmetric dielectrics, including piezoelectrics. Direct flexoelectricity is defined as the appearance of an electric field due to induced strain gradients. The numerical modeling of flexoelectricity is largely carried out using mixed FE, which has its historical foundations in strain gradient theories. However, existing finite elements are either limited to 2D or have inherited numerical instabilities due to the known saddle‐point structuring. The current work presents a numerically robust three‐dimensional mixed FE for higher‐order electromechanical applications without the use of stabilization or penalty parameters. After its verification, the new finite element is applied to the new problem of truncated semicone torsion, taking into account flexoelectricity in piezoelectric solids, and the original findings are reported. Current research reveals the complex interaction between first‐order (piezoelectricity) and higher‐order (flexoelectricity) electromechanical coupling.

Temperature-dependent dielectric and electromechanical properties of co-modified calcium bismuth titanate (CaBi4Ti4O15) ceramics

Bismuth layer-structured ferroelectrics (BLSFs), Aurivillius-type ceramics, are of great interest primarily due to their exceptionally high Curie temperature (Tc), rendering them invaluable in various applications such as sensors, actuators, transducers, and micro-electro-mechanical systems designed for elevated temperature operations, including ferroelectric Random-Access Memory applications. This study delves into the dielectric and electromechanical properties of Cobalt-modified Calcium Bismuth Titanate (CaBi4Ti4O15, CBT) (CBT-xCo, with x = 2, 4, and 6 mol%) prepared using a conventional solid-state route followed by sintering. By incorporation of Co, insignificant structural changes were observed, disclosed by X-ray Diffraction analysis. Scanning Electron Microscope micrographs unveiled highly anisotropic grains. The sintered density measured by Archimedes method was maximum for x = 6 mol% with value of 99.1 %. A temperature-dependent dielectric study disclosed that the Curie temperature of the CBT ceramics improved with the increase in Co concentration. Notably, CBT-4Co exhibited the lowest dielectric loss of 0.0967 at 1 MHz and the highest resistivity value of 0.1975 × 105 (Ω cm) at a temperature of 775 °C. Moreover, the electromechanical coupling (kp) and mechanical quality factor (Qm) measured at elevated temperatures unveiled distinctive properties, asserting the potential of the ceramics for high-temperature piezoelectric applications up to 450 °C. CBT-4Co demonstrated the highest kp, with a negligible variation at high temperature, although Qm declined. Results confirmed that CBT-4Co stands distinguished showcasing high Tc, minimal dielectric loss, and consistent electromechanical properties making it the prime candidate for electromechanical applications spanning the gamut from room temperature to elevated temperatures.

Degradable piezoelectric biomaterials for medical applications

The energy harvesting technology based on piezoelectricity promises to achieve a self-powered mode for portable medical electronic devices. Piezoelectric materials, as crucial components in electromechanical applications, have extensively been utilized in portable medical electronic devices. Especially, degradable piezoelectric biomaterials have received much attention in the medical field due to their excellent biocompatibility and biosafety. This mini-review mainly summarizes the types and structural characteristics of degradable piezoelectric biomaterials from degradable piezoelectric small-molecule crystals to piezoelectric polymers. Afterward, medical applications are briefly introduced, including energy harvester and sensor, actuator and transducer, and tissue engineering scaffold. Finally, from a material perspective, some challenges currently faced by degradable piezoelectric biomaterials are proposed.

Enhancement of electromechanical response in curved antiferroelectric AgNbO3 ceramics by flexoelectric effect

AgNbO3 is a typical antiferroelectric ceramic with weak ferroelectricity at room temperature. Due to this feature, AgNbO3 has received a lot of attention in electromechanical applications, but most of these studies have focused on the doping of other elements in AgNbO3. In this study, curved AgNbO3 ceramics were fabricated using a gravity-driven annealing process, and the field-induced strains were investigated. The curved ceramic exhibited a significantly higher field-induced nominal strain compared to a flat ceramic. Experimental results revealed that the curved AgNbO3 sample exhibited a maximum nominal strain of 1.22%, significantly surpassing the theoretical value of 0.13%. Analysis of various characterizations confirmed the presence of flexoelectricity, and flexoelectricity played an important role in the ultrahigh electromechanical response of curved AgNbO3 ceramics. Additionally, we demonstrated that curved AgNbO3 ceramics can enhance the flexoelectric coefficient. These findings suggest that curved antiferroelectric ceramics can enhance their displacement output, meeting the requirements for applications in large-strain actuators.

Intrinsic negative Poisson’s ratio of the monolayer semiconductor β- TeO2

Monolayer semiconductors with unique mechanical responses are promising candidates for novel electromechanical applications. Here, through first-principles calculations, we discover that the monolayer β- TeO2 , a high-mobility p-type and environmentally stable 2D semiconductor, exhibits an unusual out-of-plane negative Poisson’s ratio (NPR) when a uniaxial strain is applied along the zigzag direction. The NPR originates from the unique six-sublayer puckered structure and hinge-like Te–O bonds in the 2D β- TeO2 . We further propose that the sign of the Raman frequency change under uniaxial tensile strain could assist in determining the lattice orientation of monolayer β- TeO2 , which facilitates the experimental study of the NPR. Our results is expected to motivate further experimental and theoretical studies of the rich physical and mechanical properties of monolayer β-TeO2.

Tuning structural, dielectric, and ferroelectric properties of BTO-based ceramics through dual-site substitution

Different strategies for tuning the properties of ferroelectric materials have been employed for advancing electromechanical applications. Among several material synthesis techniques explored, site substitution is an effective approach. The present work focuses on Ba1-xCaxSnyTi1-yO3 (BCST) ceramics prepared by solid-state sintering route with different substitution levels (x = 0, 0.05 and y = 0, 0.09). The impact of site substitution on the properties of Barium Titanate (BTO), phase purity, structural analysis, chemical composition, dielectric, and ferroelectric properties have been studied. An ionic radii difference at A-site and B-site substitution is a key factor to achieve significant changes in physical and structural properties. X-ray diffraction patterns ensure the formation of pure phase perovskite structure in all the compositions. Raman spectroscopy indicates Ca substitution not only occurs at the A-site but also within the oxygen octahedra, adversely affecting the properties. Ca and Sn act as strong grain growth inhibitors, leading to a fine-grained and dense microstructure in BCST. While Ca substitution has a limited impact on the Curie temperature (TC), Sn substitution lowers TC in BST (54 °C) and BCST (50 °C) compared to BTO (126 °C). The Sn substitution results in the coexistence of multiple phases (rhombohedral, tetragonal and orthorhombic) in BST, enhancing its properties (ε' = 6118 at RT, Pr = 5.50 μC/cm2, Q11 = 0.060 m4/C2, d*33 = 526 pm/V) in comparison to BTO. These results acknowledge the role of substituents in lattice disruption, paving the way for chemistry-based materials design in the field of dielectric, actuator and energy storage applications.

Enhancing the piezoelectric properties and thermal stability of PMN-PMS-PSZT high-power piezoelectric ceramics through defect engineering

The development of high-power piezoelectric ceramics with superior piezoelectric properties and broad temperature usage ranges is vital for the thriving progress of electromechanical applications. However, achieving high piezoelectricity, high mechanical quality factor, and temperature stability often presents a trade-off. In this study, we present an advanced ceramic material with excellent high-power piezoelectric properties and superior temperature stability. The piezoelectric coefficient d33 reaches 348 pC N−1, the electromechanical coupling factor kp is 54%, the mechanical quality factor Qm is 1501, the dielectric loss tanδ is 0.35%, and the d33 variation is less than 10% within 25–210 °C in 0.05Pb(Mg1/3Nb2/3)O3-0.05Pb(Mn1/3Sb2/3)O3-0.9Pb0.95Sr0.05(Zr0.48Ti0.52)O3 ceramic. The excellent piezoelectricity is attributed to the enhancement of intrinsic ionic displacement and reversible domains wall motion because of symmetry-conforming short-range distribution of oxygen vacancy, while the high Qm is a result of increased domain size and oxygen vacancy. The outstanding temperature stability is related to the stable non-180°domains structure due to the oxygen vacancy pinning effect. These properties hold great potential for advanced applications, particularly for piezoelectric high-power applications requiring constant d33 over a broad temperature range.

Enhanced grain orientation degree and electrical properties in PSN-PMN-PT textured ceramics under the effect of sintering aids

In this work, texturing is proposed to improve the piezoelectric response of PSN-PMN-PT ceramics. The PSN-PMN-PT textured ceramic with a Lotgering factor F001 higher than 99% was synthesized by the liquid-phase-assisted template grain growth (TGG) method. The addition of CuO/B2O3 sintering aids improves the BT templates induced grain orientation growth behavior significantly. In comparison with its random counterpart, the Cu/B-T textured ceramic exhibits a high Lotgering factor F001 of 99% and significantly enhanced dielectric and piezoelectric responses: εr ∼ 3100, tanδ ∼ 0.8%, d33 ∼ 1030 pC N–1, d33⋅g33 ∼ 34.2 × 10–12 m2 N–1, d33* ∼ 1490 pm V–1@5 kV cm–1, Smax ∼ 0.26%@20 kV cm–1 and Hs ∼ 8.5%. In the meantime, good temperature stability is observed in the Cu/B-T textured ceramic with a variation of d33*@20 kV cm–1 and annealed d33 lower than 9.68% and 18.1% over a wide temperature range of 25–140 °C. This work shows that PSN-PMN-PT textured ceramic (Cu/B-T) has great potential for electromechanical device applications such as precision actuators, ultrasound transducers, and energy harvesters.

Ultra-thin double-layered hexagonal CuI: strain tunable properties and robust semiconducting behavior.

In this study, the freestanding form of ultra-thin CuI crystals, which have recently been synthesized experimentally, and their strain-dependent properties are investigated by means of density functional theory calculations. Structural optimizations show that CuI crystallizes in a double-layered hexagonal crystal (DLHC) structure. While phonon calculations predict that DLHC CuI crystals are dynamically stable, subsequent vibrational spectrum analyzes reveal that this structure has four unique Raman-active modes, allowing it to be easily distinguished from similar ultra-thin two-dimensional materials. Electronically, DLHC CuI is found to be a semiconductor with a direct band gap of 3.24 eV which is larger than that of its wurtzite and zincblende phases. Furthermore, it is found that in both armchair (AC) and zigzag (ZZ) orientations the elastic instabilities occur over the high strain strengths indicating the soft nature of CuI layer. In addition, the stress-strain curve along the AC direction reveal that DLHC CuI undergoes a structural phase transition between the 4% and 5% tensile uniaxial strains as indicated by a sudden drop of the stress in the lattice. Moreover, the phonon band dispersions show that the phononic instability occurs at much smaller strain along the ZZ direction than that of along the AC direction. Furthermore, the external strain direction can be deduced from the predicted Raman spectra through the splitting rates of the doubly degenerate in-plane vibrations. The mobility of the hole carriers display highly anisotropic characteristic as the applied strain reaches 5% along the AC direction. Due to its anomalous strain-dependent electronic features and elastically soft nature, DLHC of CuI is a potential candidate for future electro-mechanical applications.

Ultrahigh electrostrictive strain and its response to mechanical loading in Nd-doped PMN-PT ceramics

Electrostrictive materials play an important role in the development of high precision actuators, due to the advantages of high resolution, low power dissipation and fast response time. However, the practical application of electrostrictive materials has been hindered by their limited displacement output. To address this, we conducted a study where we doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) ceramics with Nd2O3, aiming to significantly improve the electrostrictive effect by enhancing local structural heterogeneities that disrupt the formation of long-range ordered ferroelectric domains. We obtained an optimized electrostrictive strain of 0.231 % with negligible hysteresis at an electric field of 50 kV/cm in 4 %Nd-doped PMN-PT ceramic, surpassing the performance of state-of-the-art lead-based electrostrictive ceramics. Of particular significance is that a high electrostrictive coefficients M33 = 12.2 × 10−16 m2/V2, together with a high mechanical work density of 0.035 J/cm3 and a low power dissipation of 14 %, was achieved under a mechanical prestress of 50 MPa and an electric field of 10 kV/cm. Additionally, this material exhibits excellent fatigue resistance, with less than 3 % variation over 106 operation cycles. All these findings position 4 %Nd-doped PMN-PT ceramics as a promising candidate for high-performance electromechanical actuator applications.

Neural networks-based adaptive fault-tolerant control for a class of nonstrict-feedback nonlinear systems with actuator faults and input delay

<abstract><p>This paper addresses the challenge of adaptive control for nonstrict-feedback nonlinear systems that involve input delay, actuator faults, and external disturbance. To deal with the complexities arising from input delay and unknown functions, we have incorporated Pade approximation and radial basis function neural networks, respectively. An adaptive controller has been developed by utilizing the Lyapunov stability theorem and the backstepping approach. The suggested method guarantees that the tracking error converges to a compact neighborhood that contains the origin and that every signal in the closed-loop system is semi-globally uniformly ultimately bounded. To demonstrate the efficacy of the proposed method, an electromechanical system application example, and a numerical example are provided. Additionally, comparative analysis was conducted between the Pade approximation proposed in this paper and the auxiliary systems in the existing method. Furthermore, error assessment criteria have been employed to substantiate the effectiveness of the proposed method by comparing it with existing results.</p></abstract>

Synthesis and piezoelectric properties of freestanding ferroelectric films based on barium strontium titanate

In this work, the membrane structures based on lead-free ferroelectric barium strontium titanate with composition Ba0.8Sr0.2TO3 (BSTO) were fabricated by a magnetron sputtering method. The formation of a single-phase Ba0.8Sr0.2TO3 with thickness of 300 nm sintered on Si substrate is confirmed by XRD analysis. It is shown that films without a silicon substrate exhibit ferroelectric and piezoelectric properties. The piezoelectric and ferroelectric behaviors of BSTO thin film without a silicon substrate were confirmed through a piezoelectric force microscopy and Kelvin probe force microscopy and measurements of the effective piezoelectric coefficients (d33 and d15). Images of the residual potential of polarized areas have been obtained on the membranes, which are stable over time despite the absence of a lower electrode. Additionally, a local of ferroelectric hysteresis loop has been observed. A combination of the structural and piezoelectric measurements reveals that it possible to create freestanding ferroelectric films based on Ba0.8Sr0.2TO3 system, establishing it as a promising candidate for high-performance electromechanical applications.

Synthesis and piezoelectric properties of freestanding ferroelectric films based on barium strontium titanate

In this work, the membrane structures based on lead-free ferroelectric barium strontium titanate with composition Ba0.8Sr0.2TO3 (BSTO) were fabricated by a magnetron sputtering method. The formation of a single-phase Ba0.8Sr0.2TO3 with thickness of 300 nm sintered on Si substrate is confirmed by XRD analysis. It is shown that films without a silicon substrate exhibit ferroelectric and piezoelectric properties. The piezoelectric and ferroelectric behaviors of BSTO thin film without a silicon substrate were confirmed through a piezoelectric force microscopy and Kelvin probe force microscopy and measurements of the effective piezoelectric coefficients (d33 and d15). Images of the residual potential of polarized areas have been obtained on the membranes, which are stable over time despite the absence of a lower electrode. Additionally, a local of ferroelectric hysteresis loop has been observed. A combination of the structural and piezoelectric measurements reveals that it possible to create freestanding ferroelectric films based on Ba0.8Sr0.2TO3 system, establishing it as a promising candidate for high-performance electromechanical applications.

Pseudopolymorphic Phase Engineering for Improved Thermoelectric Performance in Copper Sulfides.

Polymorphism (and its extended form - pseudopolymorphism) in solids is ubiquitous in mineralogy, crystallography, chemistry/biochemistry, materials science, and the pharmaceutical industries. Despite the difficulty of controlling (pseudo-)polymorphism, the realization of specific (pseudo-)polymorphic phases and associated boundary structures is an efficient route to enhance material performance for energy conversion and electromechanical applications. Here, this work applies the pseudopolymorphic phase (PP) concept to a thermoelectric copper sulfide, Cu2- x S (x ≤ 0.25), via CuBr2 doping. A peak ZT value of 1.25 is obtained at 773K in Cu1.8 S + 3wt% CuBr2 , which is 2.3 times higher than that of a pristine Cu1.8 S sample. Atomic-resolution scanning transmission electron microscopy confirms the transformation of pristine Cu1.8 S low digenite into PP-engineered high digenite, as well as the formation of (semi-)coherent interfaces between different PPs, which is expected to enhance phonon scattering. The results demonstrate that PP engineering is an effective approach for achieving improved thermoelectric performance in Cu-S compounds. It is also expected to be useful in other materials.

Improved electromechanical properties of Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 ferroelectric ceramics via Sm-modification

Sm-modification has recently attracted widespread attention as an optimized method for enhancing the electromechanical properties of Pb-based perovskite ferroelectrics. The present study extends the application of Sm-modification to the Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 (PNN-PZT) ceramics, aiming to improve their electromechanical properties. The impact of Sm-doping on the phase structure, microstructure, domain morphology, dielectric and piezoelectric properties was comprehensively investigated. The results demonstrate that the Sm-doping enhances the dielectric and piezoelectric properties while retaining competitive ferroelectric-paraelectric phase transition temperature (Tm). Notably, for the 2 mol% Sm-doped samples, a significant piezoelectric coefficient d33 of 1130 pC/N and a high Tm of 130 °C were achieved, accompanied by an improved dielectric constant (εr) and electromechanical coupling factor (kp). The comprehensive properties of Sm-doped PNN-PZT ceramics exceed the general trend observed in current Pb-based ferroelectric ceramics. This research confirms the effectiveness of the Sm-modification method in PNN-PZT systems, establishing it as a promising candidate for high-performance electromechanical applications.