A theoretical study of nonlinear magnetoelectric effect in magnetostrictive–piezoelectric trilayer

A novel nonlinear theoretical model is established for magnetoelectric (ME) effect in trilayer of magnetostrictive and piezoelectric phases, in which the nonlinear magnetic–mechanical coupling behavior for the magnetostrictive phase is firstly taken into account. In this theoretical model, the interface coupling parameter k is used for characterizing actual bonding conditions at the interface. The coupled magnetic–mechanical–electric effect involving linear and nonlinear coupling interactions in the ME laminated composites is numerically simulated using this nonlinear model. The numerical results predict giant ME effect for Terfenol-D based ME laminated composites. The quantitative dependences of the giant ME effect on the applied magnetic field, the piezoelectric property of piezoelectric phase, the volume fraction of magnetostrictive phase and the interface coupling parameter k are discussed in details. All of these dependences indicate that the nonlinear theoretical model established in this article can accurately capture nonlinear magnetic–mechanical–electric coupling behavior for Terfenol-D based ME laminated composites. The giant ME effect predicted for the Terfenol-D/PMN-PT/Terfenol-D composites is in excellent agreement with recent experimental data available. It confirms the validity and reliability of the obtained nonlinear theoretical model, and demonstrates the significance and necessity of considering the nonlinear magnetic–mechanical coupling behavior of Terfenol-D.     

Characterization of poly(vinylidene fluoride-trifluoroethylene) 50/50 copolymer films as a gate dielectric

Thin films of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) 50/50 copolymer were prepared by spin coating on p-Si substrate. Thermal behavior of the film was observed by measuring the film thickness with ellipsometry as a function of the temperature and abrupt volume expansion was observed at 130–150 °C. Capacitance-voltage (C-V) and current-voltage (I-V) behavior of the aluminum/P(VDF-TrFE)/p-Si MIS (metal-insulator-semiconductor) structures were studied and dielectric constant of the P(VDF-TrFE) film was measured to be about 15.3 at optimum condition. No hysteresis was observed in the C-V curve for films as deposited and annealed (70–200 °C). Films annealed at temperatures higher than the volume expansion temperature showed substantial surface roughness due to the crystallization. Flat band voltage (V_FB) of the MIS structure with as deposited films was about −0.3 V and increased up to −2.0 V with annealing. This suggested that positive charges were generated in the film. Electronic properties of the annealed P(VDF-TrFE) film at above melting temperature were degraded substantially with larger shift in flat band voltage, low dielectric constant and low breakdown voltage. Organic thin film transistor with pentacene active layer and P(VDF-TrFE) as a gate dielectric layer showed a mobility of 0.31 cm²/V·s and threshold voltage of −0.45 V.     

Growth and optical properties of Sn–Si nanocomposite thin films

The growth and optical properties of nanocomposite thin films comprising of nanocrystalline Sn and Si are reported. The nanocomposite films are produced by thermal annealing of bilayers of Sn and Si deposited on borosilicate glass substrates at various temperatures from 300 to 500 °C for 1 h in air. X-ray diffraction reveals that the as-deposited bilayers consist of nanocrystalline Sn films with a crystallite size of 30 nm, while the Si thin films are amorphous. There is onset of crystallinity in Si on annealing to 300 °C with the appearance of the (111) peak of the diamond cubic structure. The crystallite size of Si increases from 5 to 18 nm, whereas the Sn crystallite size decreases with increase in annealing temperature. Significantly, there is no evidence for any Sn–Si compound, and therefore it is concluded that the films are nanocomposites of Sn and Si. Measured spectral transmittance curves show that the films have high optical absorption in the as-deposited form which decreases on annealing to 300 °C. The films show almost 80 % transmission in the visible-near infrared region when the annealing temperature is increased to 500 °C. There is concomitant decrease in refractive index from 4.0, at 1750 nm, for the as-deposited film, to 1.88 for the film annealed at 500 °C. The optical band gap of the films increases on annealing (from 1.8 to ~2.9 eV at 500 °C). The Sn-Si nanocomposites have high refractive index, large band gap, and low optical absorption, and can therefore be used in many optical applications.     

Damping properties of epoxy-based composite embedded with sol–gel-derived Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin film annealed at different temperatures

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on Pt/Ti/SiO₂/Si substrate by sol–gel method. The effect of annealing temperature on microstructure, ferroelectric and dielectric properties of PZT films was investigated. When the films were annealed at 550–850 °C, the single-phase PZT films were obtained. PZT films annealed at 650–750 °C had better dielectric and ferroelectric properties. The sandwich composites with epoxy resin/PZT film with substrate/epoxy resin were prepared. The annealing temperature of PZT films influenced their damping properties, and the epoxy-based composites embedded with PZT film annealed at 700 °C had the largest damping loss factor of 0.923.     

Controlling the structural,microstructure and magnetic properties of barium W-type hexaferrite elaborated using tartaric acid precursor strategy

In this study, barium W-type hexaferrite (BaCo₂Fe₁₆O₂₇) nanopowders have purposefully fabricated through tartaric acid precursor method using inexpensive starting materials. In this regards, the impact of the synthesis conditions namely the annealing temperature and the Ba:Co molar ratio on the crystal structure, crystallite size, microstructure and magnetic structure was explored using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. For instance, well crystalline W-type hexaferrite was realized for the precursors annealed at a low temperature of 1100 °C for 2 h using two different Ba:Co molar ratios of 1.1:2.2 and 1.2:2.4. The crystallite size, the lattice constant, the aspect ratio as well as the unit cell volume were substantially affected with the Ba:Co molar ratio and the annealing temperature. Remarkably, the morphology of hexaferrite powders can be controlled by adjusting the annealing temperature and the Ba:Co molar ratio. Clearly, the microstructure of the formed powders was improved to a hexagonal platelet-like structure by raising the annealing temperature. Eventually, maximum saturation magnetization Ms?=?72.3 emu/g was accomplished for W-hexaferrite particles obtained with Ba:Co molar ratio 1.1:2.2 annealed at 1350 °C for 2 h. Wide coercivities (196–1097 Oe) were achieved at the different synthesis conditions.     

Influence of annealing on dielectric and polarization behavior of PVDF thick films

The polyvinylidene fluoride (PVDF) thick film has been fabricated by a solution casting method. The fabricated film is subjected to annealing at 50, 90, 100, 110 and 130?°C for 5 h. The effect of annealing on structural, crystalline, dielectric and polarization behavior is investigated. The β-phase PVDF is found to coexist with α-phase for annealing temperature upto 100?°C, after that β-phase is converted to α-phase. The film annealed at 100?°C, exhibits enhanced permittivity, reduced tangent loss and enhanced polarization. The dielectric permittivity and tangent loss of film annealed at 100?°C are ~11 and ~0.025 respectively for the frequency range of 10³–10⁵ Hz. The saturation polarization for this film is ~1.27 µC/cm². The enhanced dielectric permittivity and polarization for the film annealed at 100?°C might be attributed to increase in crystalline α and β-phase interface as well as crystalline amorphous interface. The thick film of PVDF with improved dielectric and polarization behavior could be useful for high power electronics application.     

Effects of annealing on the structural properties of indium rich InGaN films

Indium rich (In-rich) InGaN films were grown on Ge (111) substrate by plasma assisted molecular beam epitaxy with thin GaN as a buffer layer. The effects of annealing temperature and annealing time on the structural properties of In-rich InGaN films were investigated by X-ray diffraction (XRD). XRD results indicate that the as-grown InGaN films annealed at different temperatures for 1 min and 1 h respectively did not improve the film crystalline quality. But with the annealing at 750 °C and 800 °C for 1 min respectively the metallic indium was desorbed from the InGaN structure. The InGaN films annealed at higher than 660 °C for 1 h also showed the indium desorption. The InGaN film has the best film quality after annealed at 660 °C for 6 h with the full-width at half-maximum of InGaN (002) peak to be 879 arcsec. The InGaN crystalline quality started to degrade after annealed at the temperatures higher than 660 °C for 6 h.     

Post-curing effect on magnetoelectric performance of single PZT rod/continuous Terfenol-D fiber/epoxy 1-1-3 composites

A magnetoelectric (ME) composite consisting of a single PZT rod embedded in a matrix of continuous Terfenol-D fiber and epoxy medium has been fabricated and characterized. With an optimized aspect ratio of the composite rods, a large ME effect has been observed. The magnetostrictive effect of the continuous Terfenol-D fiber/epoxy medium can be enhanced by imposing an optimal pre-loading stress on the material and this pre-loading stress can be induced by suitable heat treatment. Experimental results show that the ME effect of the single PZT rod/continuous Terfenol-D fiber/epoxy composites can be enhanced significantly by a post-curing process. A thermal stress-mediated continuous fiber composite model has been used to explain the ME enhancement of the post-cured composites.     

Annealing induced reorientation of crystallites in Sn doped ZnO films

Tin doped ZnO thin films were prepared by employing a simplified spray pyrolysis technique using a perfume atomizer and subsequently annealed under different temperatures from 350 °C to 500 °C in steps of 50 °C. The structural, optical, electrical, photoluminescence and surface morphological properties of the as-deposited films were studied and compared with that of the annealed films. The X-ray diffraction studies showed that as-deposited film exhibits preferential orientation along the (0 0 2) plane and it changes in favour of (1 0 0) plane after annealing. The increase in crystallite size due to annealing is explained on the basis of Ostwald ripening effect. It is found that the optical transmittance and band gap increases with increase in annealing temperature. A slight decrease in resistivity caused by annealing is discussed in correlation with annealing induced defect modifications and surface morphology.     

Optical characterization of ZnO thin films deposited by Sol-gel method

In this paper, ZnO thin film is deposited on Pt/TiO₂/SiO₂/Si substrate using the sol-gel method and the effect of annealing temperature on the structural morphology and optical properties of ZnO thin films is investigated. The ZnO thin films are crystallized by the heat treatment at over 400°C. The ZnO thin film annealed at 600°C exhibits the greatest c-axis orientation and the Full-Width-Half-Maximum (FWHM) of X-ray peak is 0.4360°. A dense ZnO thin film is deposited by the growth of uniform grains with the increase of annealing temperature but when the annealing temperature increases to 700°C, the surface morphology of ZnO thin film becomes worse by the aggregation of ZnO particles. In the results of surface morphology of ZnO thin film using atomic force microscope (AFM), the surface roughness of ZnO thin film annealed at 600°C is smallest, that is, approximately 1.048 nm. For the PL characteristics of ZnO thin film, it is observed that ZnO thin film annealed at 600°C exhibits the greatest UV (ultraviolet) exciton emission at approximately 378 nm, and the smallest visible emission at approximately 510 nm among ZnO thin films annealed at various temperatures. It is deduced that ZnO thin film annealed at 600°C is formed most stoichiometrically, since the visible emission at approximately 510 nm comes from either oxygen vacancies or impurities.     

Formation of A15-phase in Ta/ Nb3Al0.75Ge0.25-powder - and Nb/ Nb3Al0.75Ge0.25-powder - composites and their superconducting properties

The experiments were done using a powder mixture of Nb, Al and Ge with a particle diameter of less than 50 μm which was filled into Ta- or Nb-tubes. These composites were cold-worked and heated from 400°C (10°C/min) up to 850 or 900°C and annealed 20 min on this temperature. By this heat treatment in many areas the intermetallic compound Nb(Al,Ge)3is formed within the powder mixture. After a second cold deformation the composites were annealed at 1000, 1200 or 1300°C with different annealing times. Microprobe analysis was used to investigate the phase distribution. The formation of the A15-phase was also investigated by transition temperature measurements, which were done by the inductive method. The highest transition temperature was found after 1300°C furnace annealing. Maximum critical current was achieved by short-time resistive annealing at 1200°C of 0.5 mm θ wire. The reason for the high current carrying capacity of the short-time annealed samples can be seen from the Tc-measurements which show that a A15-phase with high transition temperature is formed even after a short annealing time. Possible improvements of superconductors made from powder mixtures are discussed.     

Effect of platinum distribution on the hydrogen gas sensor properties in tin oxide thin films

Tin oxide and platinum layers were deposited on oxidized silicon wafers by ion-beam sputtering. The hydrogen gas sensing properties of undoped films and platinum-doped films were examined at 300°C for films annealed at 500°C. It was observed that the surface platinum when annealed together with the tin oxide film increased the sensitivity and reduced the response time compared with those of undoped films. Longer annealing tended to shift the optimum sensor thickness to a thicker side; the optimum thickness changed from 17 to 37 nm as the annealing time increased from 2 to 50 h. The interdiffusivity between the platinum and the tin atoms in the bulk was negligibly small at 300°C.     

用于磁传感器的新结构磁电复合材料

研究了可用于磁场传感器的磁电复合材料, 对传统的磁电复合材料进行了结构创新, 采用条状PZT和 Terfenol-D 的材料体系, 用热固树脂进行粘合, Terfenol-D 沿长度方向磁化且PZT条沿厚度方向极化。与传统的1-3型复合不同的是: 每根PZT的输出极被串联起来。在同样的磁场激励下, 新型复合材料的输出电压为相同体积的同种结构复合材料的2.2倍, 增强了材料对磁场的灵敏度和抗噪声性能。      

Effect of heat treatment on the properties of Metglas foils, and laminated magnetoelectric composites made thereof

Annealing of magnetostrictive Metglas foils, subsequently incorporated into laminated Metglas/Pb(Zr, Ti)O₃ magnetoelectric (ME) composites, is shown to result in improved magnetic properties, as well as ME coefficients. Annealing of the foils at 350 °C resulted in partial crystallization, without oxidation or magnetic cluster formation that would reduce the magnetization. Laminate composites made with these annealed Metglas foils had improved ME coefficients.     

Mechanical response of barium-titanate/polymer 0–3 ferroelectric nano-composite film under uniaxial tension

Ferroelectric polymer based 0–3 composite films are attractive for applications such as capacitors and electric energy storage devices. In this paper, deformation and fracture behavior under uniaxial tension is characterized for BaTiO₃/poly(vinyledene fluoride-trifluoroethylene) (abbreviated as BT/P(VDF-TrFE)) ferroelectric composite film. Compared with the pure P(VDF-TrFE) copolymer film, the composite film with a small volume fraction of BT powders shows an enhanced ductility in accompany with reduced stiffness and fracture strength. Scanning electron microscope (SEM) observation and X-ray diffraction (XRD) analysis are carried out to examine the morphology and microstructure change during uniaxial tension. It is demonstrated that addition of a small amount of BaTiO₃ powders into the copolymer matrix inhibits the growth of the crystallite size, causes reduction in the crystalline content and a loosely packed molecular chain structure. Consequently, the fracture strain increases while the stiffness and fracture strength decreases for the composite films.     

Reduction the leakage current through povidone-SiO<Subscript>2</Subscript> nano-composite as a promising gate dielectric of FETs

In the present study, povidone-SiO₂ nano-composite dielectric film was introduced to replace SiO₂ gate dielectric film. The organic and inorganic particles homogeneously dispersed in nano-composite film. The structure of nano-composite film was affected by annealing temperatures. By increase in annealing temperature up to 200?°C, wt% of carbon, oxygen and nitrogen increased and wt% of silicon decreased. At 240?°C, the organic phase desorbed and nano-composite structure degraded. The annealing temperature of 150?°C was suitable for adhesion between two phases. The cross-linked structure of dielectric film annealed at 150?°C led to decrease in leakage current.     

Effect of Initial Annealing Temperature on Microstructural Development and Microhardness in High‐Purity Copper Processed by High‐Pressure Torsion

The effect of the initial annealing temperature on the evolution of microstructure and microhardness in high purity OFHC Cu is investigated after processing by HPT. Disks of Cu are annealed for 1 h at two different annealing temperatures, 400 and 800 °C, and then processed by HPT at room temperature under a pressure of 6.0 GPa for 1/4, 1/2, 1, 5, and 10 turns. Samples are stored for 6 months after HPT processing to examine the self‐annealing effects. Electron backscattered diffraction (EBSD) measurements are recorded for each disk at three positions: center, mid‐radius, and near edge. Microhardness measurements are also recorded along the diameters of each disk. Both alloys show rapid hardening and then strain softening in the very early stages of straining due to self‐annealing with a clear delay in the onset of softening in the alloy initially annealed at 800 °C. This delay is due to the relatively larger initial grain size compared to the alloy initially annealed at 400 °C. The final microstructures consist of homogeneous fine grains having average sizes of ≈0.28 and ≈0.34 µm for the alloys initially annealed at 400 and 800 °C, respectively. A new model is proposed to describe the behavior of the hardness evolution by HPT in high purity OFHC Cu.     

Recrystallization behavior of a co-cast AA3xxx–AA6xxx aluminum alloy laminate — Effect of annealing conditions and cold reduction levels

The annealing behavior of a laminated AA3xxx–AA6xxx alloy system is investigated at temperatures and conditions which represent fine particle presence or dissolution in the AA6xxx (i.e. core) layer, as well as 60 or 80% cold reduction levels. The through-thickness microstructural characteristics of the cold rolled and annealed laminates are analyzed using various methods. It is found that the average grain size of the AA3xxx (i.e. clad) layer is generally finer than that of the core layer and the grains are more equiaxed in that layer for all conditions studied. The annealed microstructure of the core layer is also more strongly affected by the change in the annealing conditions. The dependencies of the average grain size and grain size aspect ratio on the annealing conditions are dictated by the presence, size, distribution and thermal stability of particles. A higher level of cold reduction results in reversing the trend of change in the grain size aspect ratios of both layers with annealing temperature in the range of 380 to 420 °C (1 h), while it yields characteristics similar to that obtained by 60% reduction when annealing is conducted for 30 s at 540 °C. These results are explained through the microstructural evolution parameters that are affected by cold rolling and annealing conditions.     

Nanocrystalline CuO thin films: synthesis, microstructural and optoelectronic properties

Nanocrystalline copper oxide (CuO) thin films have been synthesized by a sol–gel method using cupric acetate Cu (CH₃COO) as a precursor. The as prepared powder was sintered at various temperatures in the range of (300–700?°C) and has been deposited onto a glass substrates using spin coating technique. The structural, compositional, morphological, electrical optical and gas sensing properties of CuO thin films have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Four Probe Resistivity measurement and UV–visible spectrophotometer. The variation in annealing temperature affected the film morphology and optoelectronic properties. X-ray diffraction patterns of CuO films show that all the films are nanocrystallized in the monoclinic structure and present a random orientation. The crystallite size increases with increasing annealing temperature (40–45?nm).The room temperature dc electrical conductivity was increased from 10^?6 to 10^?5 (Ω?cm)^?1, after annealing due to the removal of H₂O vapor which may resist conduction between CuO grain. The thermopower measurement shows that CuO films were found of n-type, apparently suggesting the existence of oxygen vacancies in the structure. The electron carrier concentration (n) and mobility (μ) of CuO films annealed at 400–700?°C were estimated to be of the order of 4.6–7.2?×?10¹⁹?cm^?3 and 3.7–5.4?×?10^?5?cm²?V^?1?s^?1?respectively. It is observed that CuO thin film annealing at 700?°C after deposition provide a smooth and flat texture suited for optoelectronic applications. The optical band gap energy decreases (1.64–1.46?eV) with increasing annealing temperature. It was observed that the crystallite size increases with increasing annealing temperature. These modifications influence the morphology, electrical and optical properties.     

Synthesis of SiOF nanoporous ultra low-k thin film

In this work, we have investigated the effect of annealing temperature on physical, chemical and electrical properties of Fluorine (F) incorporated porous SiO₂ xerogel low-k films. The SiO₂ xerogel thin films were prepared by sol–gel spin-on method using tetraethylorthosilicate as a source of Si. The hydrofluoric acid was used as a catalyst for the incorporation of F ion in the film matrix. The thickness and refractive index (RI) of the films were observed to be decreasing with increase in annealing temperature with minimum value 156 nm and 1.31 respectively for film annealed at 400 °C. Based on measured RI value, the 34 % porosity and 1.53 gm/cm³ density of the film annealed at 400 °C have been determined. The roughness of the films as a function of annealing temperature measured through AFM was found to be increased from 0.9 to 1.95 nm. The Electrical properties such as dielectric constant and leakage current density were evaluated with capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements of fabricated Al/SiO₂ xerogel/P–Si metal–insulator-semiconductor (MIS) structure. Film annealed at 400 °C, was observed to be with the lowest dielectric constant value (k = 2) and with the lowest leakage current (3.4 × 10^?8 A/cm²) with high dielectric breakdown.