Composite Bilayer Research Articles

Magnetically tunable dielectric, impedance and magnetoelectric response in MnFe2O4/(Pb1−xSrx)TiO3 composites thin films

We have synthesized piezomagnetic–piezoelectric composites thin films MnFe2O4/(Pb1−xSrx)TiO3, where x=0.1, 0.2, and 0.3, using the metalorganic deposition (MOD) reaction method. The structural and microstructural analysis using the X-ray diffraction (XRD), AFM, and SEM reveals the presence of homogenous growth of both pervoskite and spinel phases in the composite films. Our results show that all the composites films exhibit good multiferroic as well as considerable magnetoelectric coupling. The impedance (Z′ and Z″) and electrical modulus (M′ and M″) Nyquist plots show distinct electrical responses with the magnetic field. Our analyses suggest that this electrical response arises due to the coexistence of the high resistive phase and the comparatively conductive phase in the MFO/PST composite films. The maximum magnetoelectric coefficient (α) is found to be 4.29VOe−1cm−1 and 2.82VOe−1cm−1 for compositions x=0.1 and 0.2. These values are substantially larger than those reported for bilayer composites thin films in literature and make them interesting for room temperature device applications.

Investigations of the mechanical properties of bi-layer and trilayer fiber reinforced composites

Natural fibers are renewable raw materials with an environmental-friendly properties and they are recyclable. The mechanical properties of bi-layer and tri-layer thermoset polymer composites have been analyzed. The bi-layer composite consists of basalt and jute mats, while the tri-layer composite consists of basalt fiber, jute fiber and glass fiber mats. In both cases, the epoxy resin was used as the matrix and PTFE as a filler in the composites. The developed trilayer natural fiber composite can be used in various industrial applications such as automobile parts, construction and manufacturing. Furthermore, it also can be adopted in aircraft interior decoration and designed body parts. Flexural, impact, tensile, compression, shear and hardness tests, together with density measurement, were conducted to study the mechanical properties of both bi-layer and tri-layer composites. From the comparison, the tri-layer composite was found to perform in a better way in all tests.

Enhanced converse magnetoelectric effect in cylindrical piezoelectric-magnetostrictive composites

Enhanced converse magnetoelectric (ME) effect has been experimentally observed in cylindrical PZT-Terfenol-D piezoelectric-magnetostrictive bilayered composites, where the piezoelectric and magnetostrictive components are coupled through normal stresses instead of shear stresses that act in most of previous multiferroic composites. A theoretical model based on elastodynamics analysis has been proposed to describe the frequency response of converse ME effect for axial and radial modes in the bilayered cylindrical composites. The theory shows good agreement with the experimental results. The different variation tendency of resonant converse ME coefficient, as well as different variation rate of resonance frequency with bias magnetic field for axial and radial modes is interpreted in terms of demagnetizing effect. This work is of theoretical and technological significance for the application of converse ME effect as magnetic sensor, transducers, coil-free flux switch, etc.

지르코니아 프라이머 종류에 따른 복합레진-지르코니아의 전단결합강도

Purpose: The aim of this research was to evaluate the influence of different surface treatments on the shear bond strength of zirconia ceramic to composite resin. Methods: Seventy two cylinder-shape (diameter: 5 mm; height: 12 mm) blocks of experimental industrially manufactured Y-TZP ceramic were abraded with <TEX>$125{\mu}m\;Al_2O_3$</TEX> particles and randomly divided into 4 groups. All the materials were categorized as group Gc(control group - composite resin veneering on zirconia surface), Gr - composite resin veneering after surface treatment of Rocatec system (3M ESPE, Seefeld, Germany) group; Gz - composite resin veneering after surface treatment of Zirconia primer (Z-primer, Bisco, U.S.A) group; Gm - composite resin veneering after surface treatment of zirconia primer (Monobond plus, ivoclar vivadent AG, Liechtenstein) group. Two different zirconia primers and Rocatec system were used to zirconia cylinders (n=16) onto the zirconia surface. Zirconia specimens, polished and roughened, were pretreated and composite bilayer cylinders bonded using conventional adhesive techniques. Results: Shear bond strengths were analyzed using single-factor ANOVA(p<0.05). Bond strength values achieved after airbone particle abrasion and zirconia surface pre-treatments(p<0.05). Conclusion: Shear bond strength tests denmonstrated that zirconia primer is a viable method to improved bond strength between zirconia ceramic core and veneering composites.

Tailoring microstructure and properties of bilayer-graded Al/B4C/MgAl2O4 composites by single-stage pressureless infiltration

The quantitative effect of the following parameters on the one single step pressureless infiltration characteristics of bilayer (B4C)p/rice-husk ash (RHA) porous preforms by aluminum alloys was investigated using the Taguchi method and analysis of variance (ANOVA): infiltration temperature and time, B4C particle size, RHA percentage, preform porosity and alloy magnesium content. Contribution determinations of each of the parameters on the bending strength of the resulting bilayer composites indicated that the parameter with the most significant effect is process temperature, with a contribution percentage of 79%. Verification tests conducted using the established optimum parameters show good agreement with those of projected values. A detailed examination of microstructure and potential chemical reactions, aided by thermodynamic analysis, allowed establishing conditions for suppressing or diminishing the impact of the deleterious Al4C3 phase.

Comparison of ballistic performances of Al2O3 and AlN ceramics

Finite element analysis of the impact of 7.62AP bullets on ceramic/aluminum bi-layer hybrids was carried out using AUTODYN hydrocode. Johnson–Cook material model was used for the metal and Johnson–Holmquist model was used for the ceramic. The models were validated with experiments conducted on Al2O3/Al 5083 and AlN/Al 5083 bi-layer composites. It has been observed that AlN ceramics has superior performance in defeating the bullet in comparison to Al2O3 ceramics. Deformation of the backing plate and the corresponding plastic strain energies are considered in this study for the parameters of performance. The results will enable the design of materials for developing an efficient structure for the protection against the impact of 7.62AP bullets at ordnance velocities.

Correlation Between Interfacial Structure and Toughness in SiC-Al Bilayers

Reinforcement surface modification is often used to improve the mechanical properties of particle-reinforced metal matrix composites, however, the extent to which such modifications affect the interfacial properties is yet to be revealed. In this study, we fabricated SiC-Al composite bilayers where the SiC underwent different surface treatments before Al deposition. Four-point bending tests showed that the samples made from acid-pickled and thermally oxidized SiC possessed substantially higher interfacial toughness than their untreated counterpart, a presumption inferred from mechanical tests on bulk SiCp-Al composites but never justified quantitatively. These findings were rationalized by the different interfacial constituents and structure in these samples.

A simply effective double-coating cathode with MnO2 nanosheets/graphene as functionalized interlayer for high performance lithium-sulfur batteries

Herein, we report a facile and effective adsorption strategy to improve the performance of Lithium-Sulfur (Li-S) batteries. MnO2 nanosheets grown on the surface of highly conductive graphene resulted in a coupled composite bilayer electrode when coated onto a sulfur cathode. In this way, a high initial specific capacity of 1395mAhg−1 at a rate of 0.5C, a coulombic efficiency approaching 100% and steady cyclic efficiency with a fade rate of 0.3% per cycle from 10 to 100 cycles has been achieved. This hybrid electrode not only shows enhanced electrochemical performance but can also be easily controlled and scaled thereby aiding future commercialization of high-performance Li-S batteries.

Enhancing magnetoelectric effect in multiferroic composite bilayers via flexoelectricity

We employ the flexoelectricity to enhance the magnetoelectric (ME) (coupling) effect in multiferroic (MF) composites and structures. An analytical model is presented to predict the ME effect in a MF composite bilayer consisting of piezomagnetic and piezoelectric layers. The flexoelectric effect in the piezoelectric layer is taken into account. The static ME effect in the MF composite bilayer with free boundary conditions is investigated. The results indicate that flexoelectricity can dramatically enhance the ME effect in multiferroic composites and structures.

Performance Enhancement of Small Molecular Solar Cells by Bilayer Cathode Buffer.

An effective composite bilayer cathode buffer structure is proposed for use in small molecular solar cells. CsF was doped in Alq3 to form the first cathode buffer, leading to small serial resistances. BCP was used as the second cathode buffer to block the holes to the electrode. The optimized bilayer cathode buffer significantly increased the short circuit and fill factor of devices. By integrating this bilayer cathode buffer, the CuPc/C60 small molecular heterojunction cell exhibited a power conversion efficiency of up to 0.8%, which was an improvement of 56% compared to a device with only the Alq3 cathode buffer. Meanwhile, the bilayer cathode buffer still has a good protective effect on the performance of the device.

Magnetoelectric coupling in lead-free piezoelectric Lix(K0.5Na0.5)1 − xNb1 − yTayO3 and magnetostrictive CoFe2O4 laminated composites

To replace lead zirconium titanate in magnetoelectric (ME) composites owing to concerns regarding its toxicity, we investigate the ME coupling in bilayer composites comprising lead-free Lix(K0.5Na0.5)1−xNb1−yTayO3 (LKNNT) (piezoelectric) and CoFe2O4 (magnetostrictive) phases. We prepare the LKNNT ceramics and measure its piezoelectric coefficient d31, a crucial ingredient determining ME couplings, for several Li (x=0.03,0.035,0.04) and Ta (y=0.15,0.2,0.25) concentrations, and find that the highest d31 occurs at y=0.2 for all the values of x studied here. We then evaluate both the transverse (αE,31) and the longitudinal (αE,33) low-frequency ME coupling coefficients of our composites, for each the above composition of (x,y). At x=0.03, we find the usual scenario of αE,31 and αE,33, i.e., the strongest ME coupling occurs when d31 is maximal, namely at y=0.2. On the other hand, interestingly, we also obtain the strongest ME coupling when the LKNNT layer has a relatively weaker d31, e.g., at y=0.25 for x=0.035 and y=0.15 for x=0.04, following from the interplay of d31 and other ingredients (e.g., dielectric constant). Our calculated ME couplings, with αE,31 in magnitude around twice of αE,33, are comparable to those in lead-based composites. The effect of the volume fraction and interface parameter on the ME coupling is also discussed.

Strong coercivity reduction and high initial permeability in NiCoP coated BaFe12O19–polystyrene bilayer composite

Soft-magnetic NiCoP coated hard-magnetic M-type ferrite BaFe12O19 (BaM)–polystyrene (PS) bilayer composite film was successfully synthesized. X-ray diffraction peaks exhibited no change in the structure of BaM after coating with PS. The NiCoP coated BaM–PS composite exhibited a wasp-waisted magnetic hysteretic loop with remarkable reduction in the coercivity, remanence and squareness with respect to BaM–PS, which is useful for the core of a magnetic switching device to control currents so large that they are unmanageable. Moreover, the initial permeability measurement exhibits initial permeability of around 100 000 and thermal stability up to 558 K, which is good for flux-amplifying components of smaller inductors.

The memory effect of magnetoelectric coupling in FeGaB/NiTi/PMN-PT multiferroic heterostructure.

Magnetoelectric coupling effect has provided a power efficient approach in controlling the magnetic properties of ferromagnetic materials. However, one remaining issue of ferromagnetic/ferroelectric magnetoelectric bilayer composite is that the induced effective anisotropy disappears with the removal of the electric field. The introducing of the shape memory alloys may prevent such problem by taking the advantage of its shape memory effect. Additionally, the shape memory alloy can also “store” the magnetoelectric coupling before heat release, which introduces more functionality to the system. In this paper, we study a FeGaB/NiTi/PMN-PT multiferroic heterostructure, which can be operating in different states with electric field and temperature manipulation. Such phenomenon is promising for tunable multiferroic devices with multi-functionalities.

Microstructure and properties of bilayer-graded Al-matrix composites by one-step pressureless infiltration of B4C/rice-husk ash preforms

ABSTRACTThe quantitative effect of the following parameters on the one single step pressureless infiltration characteristics of bilayer B4Cp/rice-husk ash (RHA) porous preforms by aluminum alloys was investigated using the Taguchi method and analysis of variance (ANOVA): infiltration temperature and time, B4C particle size, RHA percentage, percentage porosity in the preforms, and magnesium content in the alloy. The contributions of each of the parameters to the retained porosity, hardness and modulus of elasticity of the resulting bilayer composites were determined. The parameters that most significantly impact the modulus of elasticity (E) of the resulting composites are chemical composition of Al alloy followed by porosity of preforms and B4C particle size. Their relative contributions to the variance in the values of modulus of elasticity are 25.7, 22.48 and 18.44 %, respectively. Verification tests conducted using the established optimum parameters show a good agreement with those of projected values.

Spin-triplet superconducting current in metal-oxide heterostructures with composite ferromagnetic interlayer

Superconducting heterostructures fabricated from oxide superconductor $\text{YBa}_{2}\text{Cu}_{2}\text{O}_{7-\delta}$ and a composite ferromagnet La0.7Sr0.3MnO3/SrRuO3 interlayer and Au/Nb counter electrode were studied experimentally. Superconducting current was observed at magnetic field $H$ raised up to 2000 Oe, which is greater than saturation magnetic field of manganite La0.7Sr0.3MnO3 (of order 100 Oe) and greater by a few orders than the value of magnetic field corresponding to penetration of one magnetic flux quantum. Microwave measurements of integer and half-integer Shapiro steps in conditions when relatively low external magnetic field $H was applied showed that the second harmonic in the current-phase relation of superconducting current becomes as big as the first harmonic. Fourier analysis of $I_{C}(H)$ dependence allows extracting the components of fractional periods in $I_{C}(H)$ function that also confirms a deviation from the sinusoidal current-phase relation. The obtained experimental data are explained by theoretical models that predict a huge enhancement of the second harmonic of the spin-triplet component in the superconducting current. The current-phase relation could be controlled by an external magnetic field, changing the directions of magnetization in the composite bilayer ferromagnet, which is inserted between two spin-singlet superconductors.

Anti-reflection coatings with enhanced abrasion and scratch resistance properties

The development of multifunctional coatings plays a crucial role in the achievement of more competitive glasses for optical and solar application, among others. In this respect, coatings that provide high transmittance together with abrasion resistance could mean an added value to such glasses. Herein, we report design and preparation of novel multifunctional coatings that present anti-reflection (AR), scratch and abrasion resistance properties. This is achieved by a coating structure with a composite top layer comprising at least one type of metal oxide (ZrO2 or TiO2) or silane compound with low-refractive-index SiO2 layer. The above composite layer is applied onto a high refractive metal oxide layer, either titania or zirconia. The properties of the coatings were studied by different characterization techniques such as UV–visible–NIR spectrophotometer, FESEM, FIB, SEM–EDAX, haze and transmission meter, ellipsometer, pencil hardness tester, Taber Abrader and water contact angle measurement. The results indicate that the AR films produced by a bilayer system especially using a low refractive nanocomposite layer as a top layer and a high refractive layer as a bottom layer showed a high transmission in the visible range with comparatively better abrasion and scratch resistances. Moreover, the coatings developed on silicon wafer used as an absorber substrate for PV application exhibited an excellent low reflectance property, <2.5 % average reflection from 300 to 1500 nm which makes it applicable in both optical and photovoltaic systems with high mechanical stability. Composite bilayer anti-reflection coatings with enhanced abrasion and scratch resistance properties.

Electronic Properties of Incommensurate Atomic Layers

We present a brief theoretical overview of electronic properties of incommensurate multilayer systems, i.e., a pair of two-dimensional atomic layers stacked in an arbitrary orientation. We introduce the general theoretical scheme to describe the interlayer interaction between incommensurate crystal structures, and apply the formula to two specific examples, the twisted bilayer graphene and graphene–hBN composite bilayer. In each case, we calculate the electronic band structure and demonstrate that the low-energy electronic properties are significantly modified by the interlayer interaction, particularly when the two lattice structures are close to each other. We also study the energy spectrum and the quantum Hall effect in magnetic fields, where we see that the spectral structure exhibits a fractal nature, as known as the Hofstadter butterfly. We argue about the optical absorption properties of the twisted bilayer graphene and show that the interlayer interaction gives rise to the characteristic spectrosc...

Evolution of Voltage Transients During the Switching of a MEMS Relay With Au/MWCNT Contacts

Gold is commonly used for microelectromechanical electrical contacts due to its desirable electrical and mechanical properties; however, the lifetime of gold contacts is limited, particularly in the case of hot switching. To improve the lifetime of electrical contacts, we have developed a gold-coated multiwalled carbon nanotube bilayer composite. Experiments with these composites have shown that the switching dynamics vary over the lifetime of the switch. The change in potential across the switch contacts during the contact-break process, referred to as the transient opening voltage, has been monitored at a number of intervals throughout the switch life. The transient opening voltage shows behavior indicative of the molten metal bridge (MMB) phenomenon. While stable for most of the contact lifetime, the duration of this behavior increases sharply as the contacts approach failure. Throughout the switch lifetime, the contacts are required to survive a large number of opening and closing cycles and, therefore, it is important to understand the switching dynamics. A contact pair was investigated to failure where the experimental conditions were: load current and voltage of 50 mA and 4 V, respectively. Failure occurred after 28 million hot-switched cycles. The average energy of the MMB process was evaluated as 1.54 $\mu \text{J}$ per opening event during the stable region, this rose to 13.2 $\mu \text{J}$ shortly before failure. An experiment run under similar conditions but with a lower load current of 10 mA, which was switched for over 500 million cycles, showed a stable contact resistance and an average MMB energy of $5~\Omega $ and 57 nJ, respectively.

Unified solutions for piezoelectric bilayer cantilevers and solution modifications

Based on the theory of piezoelasticity, the static performance of a piezoelectric bilayer cantilever fully covered with electrodes on the upper and lower surfaces is studied. Three models are considered, i.e., the sensor model, the driving displacement model and the blocking force model. By establishing suitable boundary conditions and proposing an appropriate Airy stress function, the exact solutions for piezoelectric bilayer cantilevers are obtained, and the effect of ambient thermal excitation is taken into account. Since the layer thicknesses and material parameters are distinguished in different layers, this paper gives unified solutions for composite piezoelectric bilayer cantilevers including piezoelectric bimorph and piezoelectric heterogeneous bimorph, etc. For some special cases, the simplifications of the present results are compared with other solutions given by other researches based on one-dimensional constitutive equations, and some amendments have been found. The present investigation shows: (1) for a PZT-4 piezoelectric bimorph, the amendments of tip deflections induced by an end shear force, an end moment or an external voltage are about 19.59%, 23.72% and 7.21%, respectively; (2) for a PZT-4-Al piezoelectric heterogeneous bimorph with constant layer thicknesses, the amendments of tip deflections induced by an end shear force, an end moment or an external voltage are 9.85%, 11.78% and 4.07%, respectively, and the amendments of the electrode charges induced by an end shear force or an end moment are both 1.04%; (3) for a PZT-4-Al piezoelectric heterogeneous bimorph with different layer thicknesses, the maximum amendment of tip deflection approaches 23.72%, and the maximum amendment of electrode charge approaches 31.09%. The present solutions can be used to optimize bilayer devices, and the Airy stress function can be used to study other piezoelectric cantilevers including multi-layered piezoelectric cantilevers under corresponding loads.

Structural, mechanical and tribological properties of pulsed DC magnetron sputtered TiN–WSx/TiN bilayer coating

Hard-lubricious composite coatings of TiN–WSx with pure TiN under layer were deposited by pulsed DC closed field unbalanced magnetron sputtering in Ar and N2 mixed environment from separate Ti and WS2 targets. The effect of WSx content on the structural, mechanical and tribological properties of the coatings was investigated. EDS analysis of the deposited films revealed that (W+S) content varied from 6.2 to 51.6wt.%. The films were sulphur deficient with S/W at.% ratio in the range of 0.8 to 0.26. The agglomerated grain size, observed through FESEM, progressively became finer with increase in WSx content. Maximum nanohardness of 23.5GPa was obtained for the coating containing minimum content i.e. 6.2wt.% of WSx which gradually decreased with the increase in the WSx content. The adhesion of the coatings, evaluated through scratch adhesion test and indentation adhesion test, also improved with the WSx content up to 14.2wt.%, after which a gradual drop was observed. The pin-on-disc tribological test, revealed lower friction coefficient and lesser wear for the composite bilayer coatings as compared to pure TiN, with the least obtained for the coating exhibiting the maximum adhesion and an intermediate nanohardness. Raman spectra suggested the presence of soft lubricious WS2 phase in the wear debris of composite coating which resulted in less severe three-body abrasion as compared to pure TiN leading to lesser wear.