Superior Electromechanical Properties Research Articles

Single-Walled Carbon Nanotube-Reinforced PEDOT: PSS Hybrid Electrodes for High-Performance Ionic Electroactive Polymer Actuator

Ionic electroactive polymer (iEAP) actuators are recognized as exceptional candidates for artificial muscle development, with significant potential applications in bionic robotics, space exploration, and biomedical fields. Here, we developed a new iEAP actuator utilizing high-purity single-walled carbon nanotubes (SWCNTs)-reinforced poly(3, 4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT: PSS, PP) hybrid electrodes and a Nafion/EMIBF4 ion-exchange membrane via a straightforward and efficient spray printing technique. The SWCNT/PP actuator exhibits significantly enhanced electric conductivity (262.9 S/cm) and specific capacitance (22.5 mF/cm2), benefitting from the synergistic effect between SWCNTs and PP. These improvements far surpass those observed in activated carbon aerogel bucky-gel-electrode-based actuators. Furthermore, we evaluated the electroactive behaviors of the SWCNT/PP actuator under alternating square-wave voltages (1–3 V) and frequencies (0.01–100 Hz). The results reveal a substantial bending displacement of 6.44 mm and a high bending strain of 0.61% (at 3 V, 0.1 Hz), along with a long operating stability of up to 10,000 cycles (at 2 V, 1 Hz). This study introduces a straightforward and efficient spray printing technique for the successful preparation of iEAP actuators with superior electrochemical and electromechanical properties as intended, which hold promise as artificial muscles in the field of bionic robotics.

A practical stress-based test method for evaluating reversible stress limit for critical current degradation in rare-earth barium copper oxide (REBCO) tapes.

The superior electromechanical properties of second-generation high-temperature superconducting rare-earth barium copper oxide (REBCO) coated conductor tapes make them viable candidates for high magnetic field applications. To characterize their electromechanical properties (EMPs) under operating conditions, the critical current degradation behavior of the REBCO tapes should be evaluated. Conventional evaluation methods for EMPs usually rely on a strain-based test method that utilizes an extensometer to measure the deformation induced on the coated conductor tape. This study aims to establish a practical stress-based test method that determines the reversible stress limit for critical current (Ic) degradation in REBCO tapes without using extensometers under uniaxial tension. For an efficient test procedure, Ic measurements were initially performed with broad stress intervals and then changed to narrow stress intervals before the critical current degraded irreversibly. Four commercially available REBCO tape samples were used to validate the reliability of the proposed stress-based test method. It was then assessed by comparing them with those obtained using the conventional strain-based test method. Statistical estimations were used to determine the reproducibility of the results. These results provide a basis for an international round-robin test guideline to establish a test method for measuring the electromechanical properties of high-temperature superconducting tapes at cryogenic temperatures.

Ferroelectric composite-based piezoelectric energy harvester for self-powered detection of obstructive sleep

Lead-free piezoelectric ceramic is a promising material for energy harvesters, as they have superior electromechanical, ferroelectric, and piezoelectric properties. In addition, piezoelectric ceramics can be blended with polymer to achieve high-flexibility polymer-ceramic composites, providing mechanical robustness and stability. In this context, a new lead-free ferroelectric material, having the chemical formula SrTi2O5 (STO), was synthesized using a high-temperature solid-state reaction. Detailed analyses of the structural, morphological, and electrical properties of the synthesized material were performed. STO crystallizes with orthorhombic symmetry and space group of Cmm2. The frequency and temperature-dependent dielectric parameters were evaluated, and impedance spectroscopy shed light on the charge dynamics. The PDMS-STO composites at different mass fraction of the STO were prepared using a solvent casting route, and a corresponding piezoelectric nanogenerator (PENG) was developed. The electrical output of the different PENG by varying massfractions of STO in PDMS and varying force were investigated. The 15% (in mass) PENG device delivered the highest peak-to-peak voltage, current, and power density of 25 V, 92 nA, and 0.64 μW @ 500 MΩ, respectively. The biomechanical energy harvesting using the PENG device by daily human motions, bending of the device, and attaching the device to laboratory equipment was demonstrated. Later the PENG device was attached to the human throat region, and snoring signals were recorded. A classification model was designed employing the convolutional neural network (CNN) model. Efforts have been laid to differentiate between normal and abnormal snores, which could help the patient with screening and early disease detection, contributing to self-powered healthcare applications.

Applicability of ultrasonic welding to Ag-stabilized REBCO CC joints and evaluation of their electromechanical properties

Manufacturing a single long-length rare-earth barium copper oxide (REBCO) coated conductor (CC) tape with uniform critical current (I c) is still a challenge; therefore, joining between multiple-length CC tapes is needed in the production of longer CC tapes for superconducting cables, coils, and magnets. Various joining techniques have been developed to achieve acceptably low joint resistance (R j) with no I c degradation and good electromechanical properties. The authors established ultrasonic welding (UW) and hybrid welding (HW) methods for joining Cu-stabilized CC tapes with different configurations. However, these methods have yet to be applied to Ag-stabilized CC tapes to produce compact joints and longer tapes during in-line production. This study used the UW and HW methods to fabricate Ag-stabilized CC joints to have low R j without I c degradation through a direct connection at the overlapped Ag layers between both CC tapes. Two CC tape samples with different thicknesses of ∼2 µm and ∼6 µm Ag stabilizers were supplied to produce UW and HW Ag-stabilized CC joints. These were compared with soldered CC joints fabricated by a mechanically controlled soldering method. In the case of UW, the design of experiment using the Taguchi method was used to systematically determine the optimized weld parameter combination that yields a lower R j without any I c degradation. This study is a systematic attempt to evaluate the applicability of UW for solid-state joining between thin Ag layers, unlike the conventional joining of thick Cu stabilizers. Moreover, the electromechanical properties of differently processed Ag-stabilized REBCO CC joints were evaluated using both lap-shear and double-bending tests. As a result, the optimum UW parameter combinations were obtained to achieve Ag-stabilized CC joints. However, some variations were probably due to the differences in the production batch and thickness of the Ag layers. The UW Ag-stabilized CC joints showed superior joint characteristics and electromechanical properties compared to soldered CC joints. Good solid-state bonding of the Ag layers was observed through microscopic observation of the cross-section at the joint region of the UW CC joint. The joint characteristics and electromechanical properties of the UW Ag-stabilized CC joints can be further improved using the HW method.

Flexible ionic-gel strain sensor with double network, high conductivity and high frost-resistance using electrohydrodynamic printing method

Ionic-gel sensors have attracted wide attention in the fields of flexible electronic skin and wearable devices. However, the weak mechanical properties of ionic gels have hindered their large-scale applications. In this work, the electrohydrodynamic (EHD) printing method was proposed to prepare the ionic-gel film in the PDMS mold, and then the ionic-gel film with the double-network (DN) structure was formed under the induction of ultraviolet (UV) light, which greatly improved the electrical conductivity of the ionic-gel film. The CS-(AA-HEMA)-DN ionic-gel film was prepared via interpenetrating the acrylic acid and 2-hydroxyethyl methacrylate (AA-HEMA) network into chitosan (CS) network in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). The tensile strength of the CS-(AA-HEMA)-DN ionic-gel film is 0.28 MPa under 335 % strain. The electrical conductivity is 1.231 × 10-3 S/cm, and the response time is 81 ms. Therefore, the CS-(AA-HEMA)-DN ionic-gel film has excellent mechanical properties, high conductivity, and fast response time at room temperature. In addition, the CS-(AA-HEMA)-DN ionic-gel film has high frost-resistance and still has good mechanical properties, high conductivity and stability at a low temperature (−60 ℃). The CS-(AA-HEMA)-DN ionic-gel film can be used as a flexible strain sensor for monitoring human motion due to its superior electromechanical properties. Thus, the high-performance flexible ionic-gel strain sensor has broad application prospects in the field of flexible electronics.

Design and analysis of a broadband class VII flextensional transducer with the third-generation crystal, Mn:PIN-PMN-PT

For designing flextensional transducers (FTs), driving material is an important innovation direction to improve performance. The third-generation single crystal: manganese-modified Pb(In 1/2 Nb 1/2 )O 3 -Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (Mn:PIN-PMN-PT) has superior piezoelectric and electromechanical properties. However, up to date, Mn:PIN-PMN-PT single crystals applied to practical FTs haven’t been reported in the literature. In this paper, a broadband class VII FT based on [001] C poled Mn:PIN-PMN-PT is proposed. To fully utilize the excellent properties of Mn:PIN-PMN-PT, the structural parameters of the transducer were designed and optimized using the finite element method (FEM). Prototypes were fabricated and measured. Compared with the PZT-4 class VII FT, the bandwidth of the Mn:PIN-PMN-PT FT increased by 27.8%, and the transmitting voltage response (TVR) was 6.3 dB higher. This work verifies that Mn:PIN-PMN-PT single crystals have great potential as the driving material for broadband high-power FTs. • This paper proposes a broadband class VII flextensional transducer based on Mn:PIN-PMN-PT single crystals. • We fully utilize the high piezoelectric and electromechanical properties of the third-generation crystal, Mn:PIN-PMN-PT. • The acoustic performance of the Mn:PIN-PMN-PT flextensional transducer is significantly improved. • Mn:PIN-PMN-PT has great potential as the driving material for broadband high-power flextensional transducers.

Design, development and characterization of a mid-frequency (35 khz) tonpilz transducer array from 0.675PMN-0.325PT piezoceramics

A mid-frequency tonpilz transducer array was designed and analyzed by finite element method using commercial ATILA code and constructed using piezoceramic rings with lead magnesium niobate (PMN)-lead titanate (PT) composition. The morphotropic phase boundary (MPB) 0.675Pb(Mg1/3Nb2/3)O3-0.325PbTiO3 composition was chosen to obtain higher performance from the transducer due to the superior dielectric and electromechanical properties of the MPB compositions. A pure perovskite phase was obtained from the ceramics. Piezoelectric charge coefficient (d33) was measured as 435 pC×N-1. Single tonpilz element and an array consisting of 7-unit array were constructed and later potted in polyurethane for underwater measurements. A second array was also constructed for comparison from commercial hard Pb(Zr,Ti)O3-PZT ceramics. The longitudinal piston mode vibration frequency of the tonpilz transducer was measured around 33 kHz in air and around 35 kHz in water. The PMN-PT based array was found to have a comparable transmit performance and a superior receive performance compared to PZT.

The role of Nb2O5 polymorphs on processing–structure–property relationship in lead-based perovskite 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 piezoceramics

Lead-based niobate piezoceramics with perovskite structure exhibit a wide range of superior dielectric and electromechanical properties and hence are commonly used for potential commercial applications. However, the effect of Nb2O5 with various polymorphs on structure and properties of the lead-based perovskite niobates has not been studied in literature. The aim of this study was to investigate the influence of Nb2O5 with various polymorphs on the processing–structure–property relationship in lead-based perovskite 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 (PYNT) piezoceramics. The polymorphic state of Nb2O5 source dramatically affected densification, phase formation and microstructure evolution of the PYNT ceramics fabricated by applying closely controlled processing routes. Dense and pyrochlore-free PYNT ceramics with a minor amount of residual PbO were produced after sintering at 1100°C for 1 h with using 3 g atmosphere powder. Raman spectroscopy revealed that the PYNT ceramic produced using orthorhombic Nb2O5 had the most homogeneous cation ordering at the B-site as well as the least amount of the unknown phase caused by the Yb/Nb mixed compound, which resulted in up to 17% improvement in the piezoelectric and electromechanical properties with respect to the one produced using a mixture of orthorhombic and monoclinic Nb2O5. Therefore, care must be taken with initial powder characteristics, especially the crystalline structure of Nb2O5, for the sake of the fabrication of perovskite lead-based niobates with reproducible as well as enhanced properties.

High performance of polycrystalline piezoelectric ceramic-based magneto-mechano-electric energy generators

ABSTRACT The cantilever-structured magneto-mechano-electric (MME) energy generator with smaller volume exhibits excellent magnetic energy conversion performance than electro-magnetic current induction type energy harvesters. An anisotropic single crystal is an ideal piezoelectric constituent of a high-performance MME generator owing to its superior electromechanical properties and high electromechanical energy conversion efficiency. However, the complicated synthesis and high cost of piezoelectric single crystals limit the wide deployment of the MME generator. Alternatively, the implementation of the polycrystalline ceramic piezoelectric can largely reduce the device fabrication cost. In this work, the PMN-PZT single crystal fiber composites (SFC) were replaced by high-performance polycrystalline ceramic (MnO2-doped 25PMN-PZT) fiber composites (PCFC) for MME generator. The magnetoelectric response and harvested electrical power of SFC- and PCFC-based MME generators were measured. Interestingly, the electrical output power of the PCFC-based MME generator at 10 Oe magnetic field tuned at 60 Hz was found to be ~90% of that of its SFC-based counterpart, in addition to the superior thermal stability. The presented MME energy generator has excellent potential for applications as low cost and efficient power source for wireless sensor networks deployable to the internet of things (IoTs), low power consumption electronic devices, etc., by harvesting the stray magnetic energy.

Macroscopic properties of single-crystalline and polycrystalline graphene on soft substrate for transparent electrode applications

Large-area graphene synthesized by a chemical vapor deposition (CVD) method is promising for a flexible, stretchable transparent electrode but suffers from structural defects such as grain boundaries, which causes to degrade its physical properties. Recently, preparation methods of large-scale growth templates for single-crystalline graphene (SCG) were reported, but the macroscopic properties of SCG have not been adequately examined yet. Here, an SCG-based flexible, stretchable graphene transparent electrode is successfully demonstrated, which shows superior optoelectrical, electromechanical, and barrier properties compared to polycrystalline graphene (PCG)-based transparent electrodes. The result exhibits the grain boundary effect of graphene on soft substrates on a macroscopic scale and a great promise toward realizing a tremendous performance improvement of graphene-based flexible transparent electrodes on a large scale.

Fabrication of high-performance wearable strain sensors by using CNTs-coated electrospun polyurethane nanofibers

In this work, a new kind of composite nanofiber-based strain sensor with superior electromechanical properties was fabricated by using aligned thermal plastic polyurethane (TPU) nanofibers coated with multi-wall carbon nanotubes (CNTs). In order to improve the deposition efficiency and the fastness of CNTs coating on TPU nanofibers, bio-inspired dopamine (DA) was employed to modify the surface of the TPU nanofiber via a fast deposition method. (The composite nanofibers obtained were denoted as DATPU.) The electromechanical tests showed that DATPU/CNTs nanofiber membrane had a wide linear working range of 370% in the direction parallel to the nanofibers (P-DATPU/CNTs), a high gauge factor of 22.0 and a high linear coefficient of determination (r2) of 0.997. P-DATPU/CNTs nanofibers also exhibited excellent durability during stretching–releasing test for 5000 cycles. The P-DATPU/CNTs composite nanofibers demonstrated high sensing performance in detecting human motions of finger and elbow bendings.

Robust Physically Linked Double-Network Ionogel as a Flexible Bimodal Sensor.

To date, ionogel sensors have aroused the extensive interest as an alternative to hydrogel sensors, as they are promising materials to solve the problems of easy drying and easy freezing. However, the weak mechanical properties of ionogels have seriously hindered their large-scale application. Herein, a robust physically linked double-network ionogel (DN ionogel) was fabricated via interpenetrating a poly(hydroxyethyl acrylate) network into an agarose network in 1-ethyl-3-methylimidazolium chloride. The DN ionogel possessed good mechanical properties, high transparency, extreme temperature tolerance, and excellent self-adhesion. The superior electromechanical properties render the DN ionogel as a perfect candidate to be utilized as a strain sensor to monitor various human activities. In addition, the DN ionogel exhibited reasonably high sensitivity to temperature. Therefore, it is believed that this high performance strain-temperature bimodal sensor offers a promising prospect in flexible intelligent electronics.

Crossover of polar and toroidal orders in ferroelectric nanodots with a morphotropic phase boundary and nonvolatile polar-vortex transformations

Ferroelectric vortices are promising candidates for developing high-capacity memory devices and discovery of intriguing electromechanical properties. It is well known that the ferroelectric vortex state tends to stabilize at poor screening conditions and a relatively good screening condition would give rise to a polar state. However, what happens at the intermediate screening condition remains unclear. In this work, by including a Bardeen screening model into phase-field simulations, we explore the screening-mediated state stabilization in ferroelectric nanodots. A state coexistence regime where the polar and toroidal orders can both stabilize in a ferroelectric nanodot is found at certain range of screening (that is, screening length from 0.011 to 0.022 nm at room temperature). The mechanism of state coexistence is analyzed by construction of the input-dependent free-energy profile according to the energy minimum principle. The coexistence regime is further revealed to be tunable by geometrical parameters. Importantly, the polar and vortex states can be readily switched between each other via electrical and mechanical loads, paving the way towards a type of nonvolatile multilevel memory. Moreover, a screening-mediated morphotropic phase boundary (MPB) with strong dielectric and piezoelectric responses is demonstrated. Our study thus discovers a stability crossover of polar and toroidal orders in ferroelectric nanodots at intermediate screening condition accompanied with superior electromechanical properties and the feasibility in multilevel memory application.

A thermodynamic potential for barium zirconate titanate solid solutions

Barium zirconate titanate [Ba(ZrxTi1−x)O3] solid solutions are promising lead-free ferroelectric materials that have received substantial interest. Thermodynamic analysis based on phenomenological Landau–Devonshire theory is a powerful method for theoretical investigation of ferroelectric materials, but cannot be applied to Ba(ZrxTi1−x)O3 because there is no thermodynamic potential. In this paper, a thermodynamic potential for Ba(ZrxTi1−x)O3 (0 ≤ x ≤ 0.3) solid solutions is constructed, and then a thermodynamic analysis carried out. The results accurately reproduce known phase structures and their transition temperatures, with good agreement with experimentally measured polarization, dielectric, and piezoelectric constants. It is found that Ba(ZrxTi1−x)O3 solid solutions at room temperature have three phase boundaries, including a tetragonal–orthorhombic phase boundary at x = 0.013, an orthorhombic–rhombohedral phase boundary at x = 0.0798, and a rhombohedral–paraelectric phase boundary at x = 0.2135. The results also indicate that the chemical composition-induced ferroelectric–paraelectric phase boundary has superior electromechanical properties, suggesting a new way to enhance electromechanical coupling in Ba(ZrxTi1−x)O3 solid solutions.

Practical High Piezoelectricity in Barium Titanate Ceramics Utilizing Multiphase Convergence with Broad Structural Flexibility.

Due to growing environmental concerns on the toxicity of lead-based piezoelectric materials, lead-free alternatives are urgently required but so far have not been able to reach competitive performance. Here we employ a novel phase-boundary engineering strategy utilizing the multiphase convergence, which induces a broad structural flexibility in a wide phase-boundary zone with contiguous polymorphic phase transitions. We achieve an ultrahigh piezoelectric constant ( d33) of 700 ± 30 pC/N in BaTiO3-based ceramics, maintaining >600 pC/N over a wide composition range. Atomic resolution polarization mapping by Z-contrast imaging reveals the coexistence of three ferroelectric phases (T + O + R) at the nanoscale with nanoscale polarization rotation between them. Theoretical simulations confirm greatly reduced energy barriers facilitating polarization rotation. Our lead-free material exceeds the performance of the majority of lead-based systems (including the benchmark PZT-5H) in the temperature range of 10-40 °C, making it suitable as a lead-free replacement in practical applications. This work offers a new paradigm for designing lead-free functional materials with superior electromechanical properties.

Grain size dependent physical properties in lead-free multifunctional piezoceramics: A case study of NBT-xST system

Grain size effect is one of the most important issues to develop next-generation functional devices. In this work, we firstly provide a systematic investigation on the grain size dependent physical properties based on a flexible (Na0.5Bi0.5)TiO3-xSrTiO3 (NBT-xST) system with multifunctionality. The NBT-20ST, −26ST and −35ST with multiple phase boundaries/structures were chosen as the studied compositions. The densified ceramics with a series of grain sizes were successfully fabricated by normal and two-step sintering method. For NBT-20ST and −26ST compositions, the coarse grain size is more favorable for improving the direct (small-signal d33) and converse (large-signal d33∗) piezoelectricity. The critical grain size of NBT-20ST and −26ST compositions for improving d33 and d33∗ is both around 1 μm. Rayleigh analysis and local PFM mapping indicate that the high d33 in coarse-grained NBT-20ST samples originates from the increased extrinsic contribution and easier domain wall motion, while the large d33∗ in coarse-grained NBT-26ST samples stems from the polarization enhancement through a linear electrostrictive effect. For NBT-35ST composition, an improved energy storage performance with high recoverable energy density over 1 J/cm3 was achieved in a 0.56 μm-sized sample owing to a large fraction of low-polarizability grain boundary layer. This study opens up a new way for designing novel lead-free multifunctional piezoceramics with superior electromechanical properties.

Fast and Stable Ionic Electroactive Polymer Actuators with PEDOT:PSS/(Graphene⁻Ag-Nanowires) Nanocomposite Electrodes.

Ionic electroactive polymer (IEAP) actuators that are driven by electrical stimuli have been widely investigated for use in practical applications. However, conventional electrodes in IEAP actuators have a serious drawback of poor durability under long-term actuation in open air, mainly because of leakage of the inner electrolyte and hydrated cations through surface cracks on the metallic electrodes. To overcome this problem, a top priority is developing new high-performance ionic polymer actuators with graphene electrodes that have superior mechanical, electrical conductivity, and electromechanical properties. However, the task is made difficultby issues such as the low electrical conductivity of graphene (G). The percolation network of silver nanowires (Ag-NWs) is believed to enhance the conductivity of graphene, while poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which exhibits excellent stability under ambient conditions, is expected to improve the actuation performance of IEAP actuators. In this study, we developed a very fast, stable, and durable IEAP actuator by employing electrodes made of a nanocomposite comprising PEDOT:PSS and graphene–Ag-NWs (P/(G–Ag)). The cost-effective P/(G–Ag) electrodes with high electrical conductivity displayed a smooth surface resulting from the PEDOT:PSS coating, which prevented oxidation of the surface upon exposure to air, and showedstrong bonding between the ionic polymer and the electrode surface. More interestingly, the proposed IEAP actuator based on the P/G–Ag electrode can be used in active biomedical devices, biomimetic robots, wearable electronics, and flexible soft electronics.

Enhanced texture evolution and piezoelectric properties in CuO-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 grain-oriented ceramics

In this work, both crystallographic texture and doping engineering strategies were integrated to develop relaxor-PbTiO3 (PT) based ternary ferroelectric ceramics with enhanced texture evolution and superior electromechanical properties. CuO-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) piezoelectric ceramics with [001]c texture fraction ≥97% were synthesized by templated grain growth. The addition of CuO significantly promotes densification and oriented grain growth in the templated ceramics, leading to full texture development at dramatically reduced times and temperatures. Moreover, the CuO dopant remarkably enhances the piezoelectric properties of the textured ceramics while maintaining high phase transition temperatures and large coercive fields. Doping 0.125 wt. % CuO yields the electromechanical properties of d33 = 927 pC/N, d33* = 1510 pm/V, g33 = 43.2 × 10−3 Vm/N, Kp = 0.87, Ec=8.8 kV/cm, and tan δ = 1.3%, which are the best values reported so far in PIN-PMN-PT based ceramics. The high piezoelectric coefficient is mainly from the reversible piezoelectric response, with the irreversible contribution being on the order of 13.1%. We believe that this work not only facilitates closing the performance gap between ceramics and single crystals but also can expand relaxor-PT based piezoelectric application fields.

Mechanical and electro-mechanical properties of three-dimensional nanoporous graphene-poly(vinylidene fluoride) composites

Three-dimensional nanoporous graphene monoliths are utilized to prepare graphene-poly(vinylidene fluoride) nanocomposites with enhanced mechanical and electro-mechanical properties. Pre-treatment of the polymer (poly(vinylidene fluoride), PVDF) with graphene oxides (GOs) facilitates the formation of uniform and thin PVDF films with a typical thickness below 100 nm well coated at the graphene nano-sheets. Besides their excellent compressibility, ductility and mechanical strength, the nanoporous graphene-PVDF nanocomposites are found to possess high sensitivity in strain-dependent electrical conductivity. The improved mechanical and electro-mechanical properties are ascribed to the enhanced crystalline β phase in PVDF which possesses piezoelectricity. The mechanical relaxation analyses on the interfaces between graphene and PVDF reveal that the improved mechanical and electro-mechanical properties could result from the interaction between the –C=O groups in the nanoporous graphene and the –CF2 groups in PVDF, which also explains the important role of GOs in the preparation of the graphene-polymer nanocomposites with superior combined mechanical and electro-mechanical properties.

Characteristic Irreversible Critical Strain Limit of GdBCO Coated Conductor Tapes under Various Temperature and Magnetic Field Conditions

Superior mechanical and electromechanical properties of the coated conductor (CC) tapes made them a viable option for coil and magnet applications. In this study, investigation on the characteristics of I c under different B, T, and e conditions were conducted. Tensile load was applied using the Katagiri type test rig under different high magnetic field and low-temperature conditions wherein irreversible strain, e irr was determined. The I c behavior with magnetic field of both reactive co-evaporation by deposition and reaction (RCE-DR) and metal organic chemical vapor deposition (MOCVD) processed CC tapes at different T and B were obtained. The critical irreversible strain limit e irr of Cu-stabilized REBCO CC tape increased with decreasing temperature from 65 K down to 20 K. This behavior was resulted from the increased yield strength of the CC tape due to thermal hardening effect.