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A composite formed of NiO nanoflakes assembled on carbonized filter paper (CFP) has been successfully synthesized by a hydrothermal route with subsequent annealing. The CFP substrate presented a three-dimensional (3D) network structure. The composite electrode demonstrated high capacity and good cyclic and rate capabilities. It delivered a capacity of 724 mA h g−1 at current density of 100 mA g−1 after 100 cycles without apparent capacity fading during cycling. It delivered a capacity of 446 mA h g−1 even at high current density of 1000 mA g−1. The composite achieves better battery performance through ZnCl2 activation compared with conventional HNO3 activation.

Reduced graphene oxide (RGO) multilayer sheets were synthesized using waste paper pulp as carbon source. Formation of RGO was confirmed by Raman spectroscopy. RGO was mixed with cement at different concentrations (0.001, 0.01, 0.05 and 0.1% w/w) to obtain graphene cement composites (GCC). RGO is supposed to impart hydrophobicity to cement; hence, the capillary test was conducted. Hydrophobic property of GCC was found to be dependent on time, concentration and temperature. Antimicrobial property of GCC was checked which included antibacterial and antifungal studies. GCC showed better antibacterial performance (90%) against gram positive bacteria (Bacillus subtilis) than the gram-negative bacteria (Escherichia coli, 85%). Gram negative bacteria possess structurally more complex cell membranes than gram positive bacteria; hence, it was more resistant to GCC. Our finding supports the concept of involvement of membrane bound macromolecules in antibacterial performance of RGO. GCC was also found to be effective (88% inhibition) against fungal strain (Aspergillus niger).

We synthesized a flexible lithium-ion battery (LIB) anode with a flower-like CuCo2O4 nanostructure grown on the surface of conductively-treated filter paper. The filter paper, made of cotton fibers, has good flexibility, but its poor conductivity limits its application in flexible electrodes. An Ni coating by magnetron sputtering can significantly improve its conductivity, which enables it to be used as a substrate for flexible electrodes. The flower-like CuCo2O4 nanostructure is assembled from CuCo2O4 nanowires with a diameter of 50 nm, while the CuCo2O4 nanowires are assembled from CuCo2O4 nanoparticles with a size of 10–20 nm. The gap between the stacked CuCo2O4 nanoparticles causes the porous structure of the CuCo2O4 nanowires. The high theoretical capacity of CuCo2O4, the porous structure of the CuCo2O4 nanowires, and the tiny CuCo2O4 nanoparticles lead to the excellent electrochemical performance of the CuCo2O4 flower-like nanostructure. It maintains capacity very well during cycling and delivers a high capacity of 989 mAh g−1 at a current density of 100 mA g−1. As a flexible LIB anode, the composite with the flower-like CuCo2O4 nanostructure grown on the surface of conductively-treated filter paper delivers a stable capacity of 544 mAh g−1 at a current density of 100 mA g−1 and a capacity of 304 mAh g−1 at a high current density of 2000 mA g−1. The conductively-treated filter paper substrate can significantly improve the battery property of the hydrothermally-fabricated CuCo2O4.

With high carrier mobility and low cost, reduced graphene oxide (RGO) shows bright prospects for use in the field of thermoelectric materials. To investigate the intrinsic thermoelectric properties of RGO sheets, we prepared RGO papers which were reduced by HBr solution for 5 min, 20 min, and 60 min, respectively. Thermogravimetry analysis (TGA) and Raman analysis showed that the conjugated carbon network of graphene oxide (GO) was restored during the reduction process and the thermal stability of the RGO papers was much better than that of GO paper. The RGO paper that was reduced for 60 min and then annealed in Ar/H2 atmosphere exhibited the highest electrical conductivity of 3.22 × 105 S/m at 160°C. As the reduction degree of the RGO paper deepens, the Seebeck coefficient gradually transforms from positive to negative, indicating that the conduction type of RGO paper can be controlled by regulating the reduction degree.

Direct ink writing is an interesting and attractive method to replace traditional fabrication techniques such as etching, milling, and lithography for flexible electronics because of its simple process, low cost, green nature, and good prospects for development and application. In this work, graphene/polypyrrole (G/P) binary conductive material was prepared by in situ polymerization of pyrrole monomer and graphene oxide with vitamin C (VC) as green reducing agent. Then graphene/polypyrrole/carbon black (G/P/CB) conductive ink was fabricated using a mixture of alcohol, ethylene glycol, glycerol, and deionized water as solvent. Electronic circuits were obtained by directly writing the prepared conductive ink on flexible substrate, high-gloss photographic paper. When the loading of G/P binary conductive material, carbon black, ethanol, ethylene glycol, glycerol, sodium carboxymethyl cellulose, and deionized water was 54 mg, 546 mg, 12 mL, 30 mL, 30 mL, 480 mg, and 51 mL, the electrical conductivity, solid content, contact angle, and viscosity was 146.3 μS/cm, 4.3%, 34.6°, and 35.8 mPa s, respectively. The ink exhibited excellent water and acid resistance, and the electronic circuit written using the ink showed good uniformity and mechanical flexibility. Scanning electron microscopy evaluation of cross-sections of G/P/CB ink lines on photographic paper and light-emitting diode experiments confirmed that the three-dimensional flexible paper-based conductive circuits containing 9 wt.% G/P formed a complete electrical network.

A 3-dimensional carbonized multi-walled carbon nanotube (MWCNT) paper was used as the host of nano-tin oxide (SnO2) for lithium-ion batteries (LIBs). The cellulose fibers were fully mixed with MWCNTs in water. Then, the paper was obtained via vacuum filtration. Carbonization was carried out in a vacuum furnace at 1460°C. SnO2 slurry was coated on the carbonized MWCNT paper (CMP). Scanning electron microscopy (SEM) was utilized to observe the anode electrode. The images of SEM indicated that the nano-SnO2 was embedded into the holes of the porous CMP collector. This contributed the increase of contact interface area of the nano-SnO2 and the collector and the significantly reduced interface resistance. Electrochemical tests showed that the initial discharge capacity reached 1745 mAh g−1 with a coulumbic efficiency (CE) of 70.39% at a current density of 50 mA g−1. The composite electrode still maintained a reversible capacity of 753 mAh g−1 with a CE of 98% at a current density of 200 mA g−1 after 100 cycles. These marvelous composite electrodes exhibited a promising future for the next generation of LIBs.

Direct deposition of hydrogenated amorphous silicon (a-Si:H) thin films and fabrication of solar cells on polyimide (PI) and photo-paper (PP) substrates using a rf-plasma-enhanced chemical vapor deposition technique is reported. Intrinsic amorphous silicon films were deposited on PI and PP substrates by varying the substrate temperature (Ts) over 70–150°C to optimize the deposition parameters for best quality films. The films deposited on both PI and PP substrates at a temperature as low as 70°C showed a photosensitivity (σph/σd) of nearly 4 orders of magnitude which increased to 5–6 orders of magnitude when the substrate temperature was increased to 130–150°C. The increase in σph/σd is due to the presence of a few nanometer-sized crystallites embedded in the film. Solar cells (n-i-p) were fabricated directly on PI, PP and Corning 1737 glass (Corning) at 150°C for different thicknesses of an intrinsic amorphous silicon layer (i-layer). With the increase in i-layer thickness from 330 nm to 700 nm, the solar cell efficiency was found to increase from 3.81% to 5.02% on the Corning substrate whereas on the flexible PI substrate an increase from 3.38% to 4.38% was observed. On the other hand, in the case of cells on PP, the i-layer thickness was varied from 200 nm to 700 nm and the best cell efficiency 1.54% was obtained for the 200-nm-thick i-layer. The fabrication of a-Si (n-i-p) solar cells on photo-paper is presented for the first time.

Graphite-based composites are commonly used as an anode and current collector for energy storage devices; however, they have inherently limited potential for large scale rechargeable systems due to a brittle structure. In this study, flexible and light-weight graphite-based electrodes are prepared by incorporation of lignocelluloses fibers directly collected from a self-growing plant, Typha Angistifolia. Electrical properties of graphite and lignocelluloses composite sheets are enhanced by electrodeposition of gold in a three-electrode setup. Electrochemical deposition of gold on a lignocelluloses/graphite paper electrode was obtained in potentiostatic mode by the application of reduction potential −0.95 V for 2000 s, 600 s, and 100 s. The gold-deposited paper electrodes showed efficient kinetics by shifting redox peaks towards lower potentials in cyclic voltammetry measurements, whereas impedance measurements revealed seven orders of magnitude reduction in the resistive properties. Incorporated flexibility and superior electrical/electrochemical performance within presented graphite-based composites will provide cutting-edge characteristics for high-tech application of energy storage devices by keeping a focus on modern disposable technology.

This paper focuses on the use of alternative insulating oil due to the lack of petroleum resources and concern about the environmental issues. For these purposes, a few vegetable oils available in Bangladesh are investigated for their electrical and physical properties. Vegetable oils are environmentally friendly because of their high biodegradability, low toxicity, high flash points and lower inflammability. This paper demonstrates the kinematic viscosities of sunflower oil, til oil and pithraj oil, which are found as 22.48 mm2/s, 24.81 mm2/s and 29.84 mm2/s, respectively at 20°C. The electrical breakdown voltage obtained for sunflower oil, til oil and pithraj oil are found to be 18.53 kV, 16.17 kV and 15.03 kV, respectively, for a 2.5-mm gap between electrodes at 20°C. The statistical analysis of the breakdown voltage of the vegetable oils is conducted in this paper using ‘R’ software. Finally, the experimental results are compared with mineral oil, which is generally used in distribution transformers.

Laser treatment of graphene oxide solution among other techniques is a well-established technique for producing reduced graphene sheets. However, production of high-quality ultra-low sheet resistance reduced graphene oxide (rGO) sheets in solution has been a challenge due to their high degree of randomness, defect-rich medium, and lack of controlability. Recent studies lack an in-depth analytic comparison of laser treatment parameters that yield the highest quality rGO sheets with a low defect ratio. Hence, in this study, we implement a comprehensive comparison of laser treatment parameters and their effect on the yielded rGO sheets from an electronic and physical standpoint. Ultra-low sheet resistance graphene oxide sheets were fabricated using ultrafast laser irradiation with different laser pulse energies in the range of 0.25–2 mJ. Laser treatment for 10 min using a pulse energy of 1 mJ resulted in an increase in the defect spacing, accompanied by a large red shift in the optical absorption of the C=C bond, indicating significant restoration of the sp 2 carbon bonds. These enhancements resulted in a significant reduction in the electrical resistance of the rGO flakes (up to 2 orders of magnitude), raising the electron mobility of the films produced using the irradiated graphene oxide a step closer to that of pristine graphene films. From this study, we can also deduce which exposure regimes result in the fabrication of quantum dots and continuous defect-free films.

Supercapacitors represent an attractive alternative for portable electronics and automotive applications due to their high capacitance, specific power and extended life. In fact, the growing demand of portable systems and hybrid electric vehicles, memory protection in complementary metal-oxide-semiconductor (CMOS), logic circuit, videocassette recorders (VCRs), compact disc (CD) players, personal computers (PCs), uninterruptible power supply (UPS) in security alarm systems, remote sensing, smoke detectors, etc. require high power in short-term pulses. Therefore, in the last 20 years, supercapacitors have been required for the development of large and small devices driven by electrical power. In this paper, graphene oxide (GO) was synthesized by improved Hummers method. Two polyaniline (PANI)/graphene oxide nanocomposites electrode materials were prepared from aniline, GO and ammoniumpersulfate (APS) by in situ chemical polymerization with the mass ratios (mGO:mAniline) 10:90 and 30: 70 in ice bath. The crystal structure and the surface topography of all materials were characterized by means of x-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), Raman spectroscopy and scanning electron microscopy (SEM). The electrochemical properties of the composites were evaluated by cyclic voltammetry (CV), charge–discharge measurements and electrical impedance spectroscopy (EIS), respectively. The results show that the composites have similar and enhanced cyclic voltammetry performance compared with pure PANI based electrode material. The graphene/PANI composite synthesized with the mass ratio (mANI:mGO) 90:10 possessed good capacitive behavior with a specific capacitance as high as 1509.35 F/g at scan rate of 1 mV/s in scanning potential window from −0.8 V to 0.8 V.

RGO–RGONRs–Zn2SnO4 composite with three-dimensional (3D) hierarchical structure has been formed from Zn2SnO4 nanoparticles grown on conducting reduced graphene oxide (RGO) and reduced graphene oxide nanoribbons (RGONRs) via a chemical co-reduction process. The presence of the RGONRs in this unique hybrid nanostructure prevents restacking of the graphene sheets and provides additional electron transport paths. Lithium-ion batteries using this 3D RGO–RGONRs–Zn2SnO4 composite as anode material displayed enhanced rate capability (510.6 mA h g−1 even at 1600 mA g−1) and cycling properties (779.8 mA h g−1 after 50 cycles at current density of 200 mA g−1).

Reduced graphene oxide/copper phthalocyanine nanocomposites are successfully prepared through a simple and effective two-step method, involving preferential reduction of graphene oxide and followed by self-assembly with copper phthalocyanine. The results of photographs, ultraviolet visible, x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy show that the in situ blending method can effectively facilitate graphene sheets to disperse homogenously in the copper phthalocyanine matrix through π–π interactions. As a result, the reduction of graphene oxide and restoration of the sp 2 carbon sites in graphene can enhance the dielectric properties and alternating current conductivity of copper phthalocyanine effectively.

Graphene (GE)- or graphene oxide (GO)-based poly(vinyl alcohol) (PVA) nanocomposite membranes have been prepared by the solution blending method. Raman spectra and atomic force microscopy images confirmed that GE and GO were synthesized with average thickness of 0.901 nm and 0.997 nm, respectively. X-ray diffraction patterns indicated good exfoliation of GE or GO in the PVA matrix. Fourier-transform infrared spectra revealed the chemical fractions of the nanocomposite membranes. Differential scanning calorimetry results proved that the thermal stability of the nanocomposite membranes was enhanced compared with neat PVA membrane. Transmission electron microscopy images revealed good dispersion of GE or GO sheets in the PVA matrix with thickness in the range of 19 nm to 39 nm. As a result, good compatibility between GE or GO and PVA was obtained at 0.5 wt.% filler content.

Opening the band gap of graphene is among the most important issues in modulating its electrical properties for electronic device applications. In this study, we report on the synthesis of nitrogen-doped graphene for field effect transistors. The graphene doped with nitrogen was synthesized by thermal chemical vapor deposition using a single liquid precursor of dimethylformamide, which contains both carbon and nitrogen sources. Material characterization by Raman spectroscopy, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy confirmed the successful synthesis of high-quality nitrogen-doped graphene with a thickness of two or three atomic layers. By simply using dimethylformamide as a liquid precursor, we could dope N into graphene with a doping level of 0.64 at.%. The synthesized graphene was used to fabricate a field effect transistor, the characteristics of which were systematically studied at different temperatures (15–105°C) in air and in a vacuum. Results showed that the synthesized graphene exhibits p-type behavior in air but n-type behavior in a vacuum with a band gap of about 0.03 eV. The field effect mobility calculated at room temperature was 359 cm2 V−1 s−1. The fabricated field effect transistor has potential applications in electronic devices.

The ascending trend of Moore’s law has stretched to the horizon, where the prospects of carbon-based materials show the potential of replacing the silicon-based complementary metal-oxide semiconductor technology. These alternatives include nanowire transistors, carbon nanotube field-effect transistors, quantum-dot cellular automata, and graphene nanoribbon field-effect transistors (GNRFETs). This paper presents a review of the evolution of graphene, its fabrication process, and graphene-based field-effect transistor device structures. The diverse features of graphene as a material are derived from its structural, electronic, and thermal properties. A brief review of the techniques utilized for the fabrication of GNRFETs is mentioned in this paper. GNRFETs are based on excellent electrical properties that include strong ballistic transport, high current ratio, better compatibility with high K dielectrics, high electron mobility, reliability, scalability, and transconductance. GNRFET structures are reviewed for several aspects which include the Ion/Ioff ratio, subthreshold swing, oxide thickness, high K dielectrics, etc. that help to monitor the improvement in the performance of GNRFET devices. A comparison of the structures is presented to help researchers have a fair idea of the impact of modifications on device performance. The compact model used to simulate GNRFET-based devices is also included in this paper. GNRFET-based devices have several applications to offer in the current scenario. This paper also reports several applications of present GNRFET-based devices.

The use of low-potential energy sources is an urgent problem of our time, as more than 70% of the energy used by mankind is lost in the form of low-potential waste. A promising technology of converting such thermal energy into electricity is the thermoelectric method. The scale of use of any technology depends on its efficiency. The problem of TEG efficiency can be divided into two separate tasks—the task of creating efficient thermoelectric materials, and the task of optimizing the parameters of thermoelectric devices. In real conditions the last task plays a significant, often crucial, role. Therefore, many works are devoted to their research. The fundamental basis for solving this problem is the mathematical modeling of the thermoelectric generator circuit, which includes a heat source, a thermoelectric converter, a cooling system, and a payload. In this paper the author presents some generalized results of previous research that can benefit the developers of thermoelectric devices. The first part of the article presents the basics of the methodology used. Next, I draw attention to the possibility of better tuning of the properties of thermoelectric materials to a specific task in case of considering external conditions. The final part of the paper provides an assessment of technical and economic indicators of TEG and formulates the conditions under which this technology can ensure competitiveness in the modern energy market.

In this paper, we reduce the self-heating effects of high-electron-mobility transistors (HEMT) by using changes in material and structure. In the first step, the 6H-SiC layer is used both as a substrate layer and as a passive layer. The thermal conductivity of SiC materials is very high, which reduces the heat under the gate. In the second step, the barrier layer is used by a combination of AlGaN and InGaN as a heterojunction. InGaN material is used at the point where the hot spot occurs. These changes in the barrier layer cause the heat to be uniformly distributed under the gate, so that the combination and recombination of electrons and holes in the hot spot are reduced. In the next step, the heat generated in the structure is directed to outside of the structure by a metal plate or field plate. In this paper, the selected structure for reference is fabricated in recent years. Different layers of materials have been grown on the Si substrate layer (AlGaN/GaN/Si). After the changes, the output current increased by 25%, and overall the heat generated in the structure decreased by 40%. The proposed structure is suitable for high-power and high-frequency circuits.

This paper presents a study of physical and electrochemical properties relevant to the lithium ion diffusion process governing WO3 thin films electrochromic phenomenon. The films were prepared from a solution obtained by the sol–gel process and deposited via dip-coating. They were characterized by chronocoulometry, chronoamperometry and in and ex situ ultraviolet–visible spectroscopy during coloring/bleaching of the films. To analyze the experimental data, a mathematical model was applied considering a reaction kinetics controlled by the diffusion of ion pairs. The effects of the intercalation of Li+, Na+ and K+ ions was compared. Theoretical and experimental results for the current, charge density and absorbance profiles in function of time are included in this paper. The highest values obtained were $$ \eta = 29.98\,{\text{C/cm}}^{2} $$ for electrochromic efficiency, ΔT = 61.6% for optical modulation, $$ Q_{i} = 81.78\,{\text{mC/cm}}^{2} $$ for charge density, and reversibility of coloring/bleaching in the range of 75–90%. X-Ray diffractometry measurements confirmed the amorphous structure of the films. Fourier transform infrared spectroscopy was employed to analyze the functional groups present in the films structure, while their topology was studied via atomic force microscopy. The collected results confirmed a relationship between the electrochromic and electrochemical reactions, definitively associating color change with cations injection and the reduction of W6+ to W5+.

In this paper, the growth of intermetallic compound (IMC) layers is considered. After soldering, an IMC layer appears and establishes a mechanical contact between eutectic tin-silver solder bumps and Cu interconnects in microelectronic components. Intermetallics are relatively brittle in comparison with copper and tin. In addition, IMC formation is typically based on multi-component diffusion, which may include vacancy migration leading to Kirkendall voiding. Consequently, the rate of IMC growth has a strong implication on solder joint reliability. Experiments show that the intermetallic layers grow considerably when the structure is exposed to heat. Mechanical stresses may also affect intermetallic growth behavior. These stresses arise not only from external loadings but also from thermal mismatch of the materials constituting the joint, and from the mismatch produced by the change in shape and volume due to the chemical reactions of IMC formation. This explains why in this paper special attention is being paid to the influence of stresses on the kinetics of the IMC growth. We develop an approach that couples mechanics with the chemical reactions leading to the formation of IMC, based on the thermodynamically sound concept of the chemical affinity tensor, which was recently used in general statements and solutions of mechanochemistry problems. We start with a report of experimental findings regarding the IMC growth at the interface between copper pads and tin based solder alloys in different microchips during a high temperature storage test. Then we analyze the growth kinetics by means of a continuum model. By combining experiment, theory, and a comparison of experimental data and theoretical predictions we finally find the values of the diffusion coefficient and an estimate for the chemical reaction constant. A comparison with literature data is also performed.

A graphene-based flexible filter was obtained via one-step laser heating of a polyimide film. The key parameters of a laser have been confirmed by comparing simulated results and experimental data. High-frequency components of input signals were filtered out effectively for different waveforms, such as sine, rectangular, triangle and pulse waveforms. In order to study filtering performance, this paper focused on amplitude frequency curve, phase frequency curve, transient response and mechanical stability. The phase frequency curve is linear distribution, indicating that it is convenient to control phase shift. The mechanical stability of the device remains good even after 5000 bends, which is unreported in previous work. This paper demonstrated that a graphene-based flexible filter prepared by one-step laser heating has excellent performance and opens new way of thinking about flexible electronics in the future.

This paper presents a systematic study of Al0.23Ga0.77N/GaN/AlxGa1−xN double-heterojunction high-electron-mobility transistors (DH-HEMTs) with a boron-doped P+ GaN cap layer under the gate. The boron-doped GaN cap layer shows great potential to form a high-bandgap Schottky gate in DH-HEMT devices to increase the resistivity of the GaN cap with excellent structural characteristics. Thus, the polarization-induced field in the GaN cap layer can be used to raise the conductive band of the device in the normally OFF operation. In this paper, these AlGaN/GaN power-switching devices with freewheeling Schottky barrier diodes are examined in their working states. In comparison with conventional HEMT power devices, the HEMT with a B-doped GaN cap offers the lowest switching charges, area-specific ON-state resistance, and energy losses. Therefore, this study clearly shows the advantage of GaN transistors for power electronics applications.

This paper presents the production of nickel ferrite powder synthesized by a sol–gel technique modified by ionic coordination reaction. Morphological powder characterization is presented via X-ray diffraction, scanning electron microscopy and energy-dispersive spectrometry. Bulk manufacturing by uniaxial press is developed, and its electrical characterization is shown. Three ferrite bulks were manufactured and characterized to evaluate the quality of the compression procedure. Permittivity and conductivity parameters were obtained and discussed according to reference papers. Characterized bulks were applied as a microstrip patch antenna with rectangular and circular geometries, designed by transmission line and cavity methods, respectively, to evaluate bulk features as substrate. Reflection coefficient and radiation patterns were simulated by a high-frequency structure simulator, and measurements of reflection coefficient were performed. The obtained radiation patterns presented good agreement between them and were consistent with the performed design. A maximum gain of 1.55 dB in the E plane could also be achieved despite the relatively high $$ tg\left( \delta \right) $$ for radiating devices. Simulated cross-polarization results are also displayed, where the maximum value obtained was −29.35 dB, highlighting the device's directivity. Good agreement between simulated and measured reflection coefficient was achieved in both geometries, reinforcing the high-quality ferrite powder production process. It was possible to reach 0.00% relative error between simulated and measured resonance frequency in one of the three circular patch devices, at 6.05 GHz. Maximum resonance frequency error presented in all performed measurements is 6.51%, associated with manufacturing and measurement issues. Despite that, the quality of the synthesized material could be observed in each discussed result.

During thermal design in the first phases development, thermoelectric systems, such as thermoelectric generators, the most important parameter affecting the performance is thermal resistance of the components. This paper focusses on the thermal contact resistance (TCR), analyzing the influence of aging and temperature on different thermal interface materials (TIMs), i.e., thermal paste, graphite and indium. In previous papers, TCR has been studied depending on parameters such as surface roughness, bonding pressure, thermal conductivity and surface hardness. However, in thermoelectric applications, a relevant aspect to consider when choosing a TIM is aging due to thermal stress. The exposure of this type of material to high temperatures for long periods of time leads to deterioration, which causes an increase in the TCR impairing the conduction of the heat flow. Therefore, there is a need to study the behavior of TIMs exposed to temperatures typical in thermoelectric generators to make a correct selection of the TIM. It has been observed that exposure to temperatures of around 180°C induces a significant increase in the thermal impedance of the three TIMs under study, although this effect is much more relevant for thermal paste. The contact, comprising steel, thermal paste and ceramic, presents a 300% increase in the thermal impedance after 70 days of aging, whereas that exceeds 185% for the contact of aluminum, thermal paste and ceramic. In the tests with exposure temperature of 60°C, there is no observed decrease in the thermal impedance. The authors are indebted to the Spanish Ministry of Economy and Competitiveness, and the European Regional Development Fund for economic support to this work, included in the RTI2018-093501-B-C22 research project.

Polymer composites have been a material of choice for lightweight and durable applications in sectors ranging from automobile, packaging, structural components, and electronics to energy harvesting. Their versatility and ability to be tailored to application requirements have made them prospective alternatives for metal enclosures used in communication systems, power electronics, electric motors, and generators. The easy processing and high strength-to-weight ratio provide advantages over traditional materials that involve time- and-labor intensive processes. However, high thermal conductivity (TC) and electromagnetic interference (EMI) shielding are factors limiting their penetration into niche markets, and thus the development of alternatives with high TC and EMI shielding efficiency is critical. Thermally conductive polymer composites and EMI shielding effectiveness (SE) is a current issue in different applications including polymers providing light weight, corrosion resistance, and ease of processing as compared with metal. This paper focuses on improvements in the TC and shielding effectiveness of polymers by incorporating various fillers including carbon-based, mineral-based, and hybrid fillers. The paper reviews the current research worldwide regarding the enhancement of the TC and shielding effectiveness of polymer composites.

A method to extract complex permittivity of liquids using a coplanar waveguide fed open stub resonator is proposed in this paper. A quarter-wave long open stub printed on a substrate is used as the sensor for the computation of complex permittivity. The free-standing unloaded sensor is designed to operate at 1.8 GHz and resonates at a lower frequency when immersed in a test liquid. The resonant frequency and the reflection phase from the sensor are recorded for the computation of real and imaginary parts of the permittivity of the test sample. The simulated response of the sensor, when immersed in liquid samples of different permittivities, is validated by measurements. Equations␣for the extraction of real and imaginary values of permittivity are also presented in this paper. The experiments demonstrate that the sensor is capable of characterizing complex permittivity of liquids with minimal error.

In order to improve the resistive switching performance of SiO2-based resistance random access memory (RRAM) devices, the evolution from pure oxide-based devices to metallic nanoparticle dispersed oxide-based devices is investigated in this paper. It is found that a high ratio of dispersed-oxide/pure-oxide and thin SiO2 film can increase the uniformity and endurance of RRAM devices. Pure TiN/SiO2/Au RRAM devices show large distributions and poor endurance for repeated resistive switching process, while the TiN/SiO2:FePt/SiO2/Au RRAM devices exhibit higher uniformity and better endurance. Moreover, the fluctuations and degradation of high-resistance state and low-resistance state are observed in the former devices; by increasing the ratio of dispersed-oxide/pure-oxide in TiN/SiO2/SiO2:FePt/SiO2/Au, high consistency resistive switching is obtained. It is believed that the random formation of conducting filaments (CFs) causes poor performance of RRAM devices, and with a higher ratio of dispersed-oxide/pure-oxide the morphology of CFs is controlled due to the local field enhancement. The results in this paper may provide a method of fabricating high-performance RRAM devices for industry application.

The vital utilization of biosensors in different domains has led to the design of much more precise and powerful biosensors, since they have the potential to attain information in a fast and simple manner compared to conventional assays. The present review describes the basic concepts, operation, and construction of biosensors and presented an ideology that choice of categorization, selection of immobilization method and advantages are crucial factors for an efficient and commercial biosensor. Amongst various biosensors, the field effect transistor (FET)-based biosensors have shown much more potential and immense advantages such as high detection ability and sensitivity for both neutral and charged biomolecules and, hence, have been explored comprehensively in the present review. This paper discusses the current challenges in device design by mainly focusing on the quantitative and qualitative performance parameters such as sensing surface properties, signal-to-noise ratio and various other factors, since consideration of these factors will eventually address the crucial concerns related to device design and practical limitations. The critical measures to translate the commercialization of biosensors in the market at a high pace have also been discussed. Hence, the discussion on device challenges illustrates that there is a scope of improvement in the areas such as short-channel effects, specificity and nanocavity filling factor for revolutionary advances in FET-based biosensors. Optimal selection of design rules and biosensing material has the potential to feature the next generation of biosensors. The present paper reports that following integrated multidisciplinary approaches and switching to nanotechnology in designing of FET-based biosensors can offer a lot of improvements in the practical key factors (such as low cost and reliability) and opportunities for the biosensors in the marketplace.

Thermal interface materials (TIMs) play a key role in reducing thermal resistance between jointed solid surfaces in order to increase thermal transfer efficiency. A TIM is a thermally conductive material which is applied between the interfaces of two components (such as circuit board and heat sinks) to enhance the thermal conductance between them. The present paper provides a detailed review in order to characterize conventional and advanced TIMs in terms of thermal performance. The paper also discusses the measurement of TIM performance using different techniques. It was found that greases are the most widely used TIMs and offer thermal resistance in the range of 0.1–1 cm2°C/W. However, greases are messy and difficult to apply and remove due to their high viscosity. Moreover, they have reliability issues such as pump-out, phase separation and dry-out, which limits their use as an efficient TIM. The thermal resistance of TIMs which contain carbon nanotubes (CNT) fall in the range of 0.01–0.19 cm2°C/W. However, the use of CNT as a TIM at high temperatures does not allow for uniform distribution of heat on cooling of electronic packaging systems. Although TIMs with the addition of nano--metal particles are considered promising, it is necessary to carry out extensive research on CNT as a TIM.

In this paper, we investigate supercapacitor behavior properties of MnO2/RGO nanocomposite thin film. The graphene thin film is deposited on the silver paper as a conductive substrate using electrochemical deposition. MnO2 nanostructure is also deposited on reduced graphene oxide, due to its high theoretical specific capacitance (1370 F g−1), through an electrochemical deposition process. The as-prepared MnO2 and MnO2/RGO nanocomposite thin films are characterized by atomic force microscopy, Raman spectroscopy, scanning electron microscopy and x-ray diffraction and based on achieved results a hybrid supercapacitor electrode is assembled. The electrochemical behaviors of the supercapacitor systems are estimated by cyclic voltammetry analysis. The experimental result, indicate that the synergistic effect between the high conductivity of graphene and pseudocapacitance of MnO2 generates large capacitance for our synthesized nanocomposite. The MnO2/RGO/Ag nanocomposite (300 F g−1) exhibits higher capacitance performance than MnO2/Ag (70 F g−1) in 1 M Na2SO4 aqueous solution.

According to the infrared attenuation spectrum, we can know the conduction type and major point defect of CdZnTe crystals. Based on point defect modelling, an appropriate modus of atmosphere annealing was described in this paper. In this paper, annealing with Cd pressure control technology was used to upgrade p-CdZnTe and n-CdZnTe, respectively. Characterizations reveal that the optical and electrical performance of the CZT crystals is patently improved after annealing. Employment of the infrared attenuation spectrum as the annealing guideline has been verified to be feasible and effectual in this paper.

A general theoretical model of thermoelectric generation (TEG) is proposed based on the one-dimensional steady heat transport in this paper. The effect of heat convection between the thermoelectric legs and the ambient environment, and contact resistance between the heat reservoirs and thermoelectric couple on the performance of the TEG is studied. Fundamental formulas and closed-form solutions for the output power and conversion efficiency are derived. Numerical results show that the maximum output power and maximum conversion efficiency of the TEG are lower than those of the ideal TEG when the influence of heat convection and contact resistance are taken into consideration. The heat convection has a very small effect on the maximum output power, but causes a large reduction of conversion efficiency for the TEG, and this reduction becomes more significant as the length of thermoelectric couple increases. In addition, there always exists an optimum length of thermoelectric couple for the actual TEG, so as to achieve the maximum conversion efficiency when the effects of heat convection together with contact resistance are considered. The results of this paper may help to improve the design and optimization of TEG devices.

The Shockley–Read–Hall (SRH) mechanism might be a limiting factor of an infrared (IR) photodiode's dark current. This limitation is twofold. SRH generation might occur in the depletion region of the photodiode. In that case, the corresponding current is usually limiting the low-temperature dark current. Moreover, SRH generation might also occur in the diffusion volume, close to the space charge region, resulting in an increase of the diffusion dark current, usually limiting the high-temperature behavior of the photodiode. Hence, the determination of the SRH lifetime of IR materials is of first importance and has to be measured (or at least estimated) to define upcoming trends in future high-performance IR detectors. During the last few years, a lot of papers have been published about SRH lifetime in III–V materials (InSb, superlattices, InAsSb) and a few other communications have been more focused on comparing different material systems including III–V and II–VI materials. Those latter communications proposed very long SRH lifetimes (longer than ms) for HgCdTe, instead of the classical 10–100 μs usually admitted until now. This paper aims at investigating this SRH lifetime in HgCdTe based on experimental measurements carried out at the Laboratoire d’electronique des technologies de l’information (LETI) on HgCdTe grown in-house. Direct lifetime measurement (photoconductive or photoluminescence decay) as well as indirect estimations from photodiode dark currents are discussed in order to clarify this question of SRH lifetime and its consequences in upcoming advanced IR detection structures. In the end, it appeared that except for p/n extrinsic heterojunctions (for which the narrow gap depleted volume is not well known), most of the devices tested seemed limited by SRH lifetimes in the 10–100-μs range.

The design, fabrication, analysis and measurement of the modulated pencil-drawn U-shaped piezoresistive graphite on paper compound fibers and its application for wind speed sensing are reported. We found that pencil drawing was a facile method for producing an ultrafine graphite film through the friction between the pencil leads and paper fibers. The pencil-drawn graphite was characterized by Raman spectroscopy and x-ray diffraction. The resistance of the patterned graphite sensor showed a decrease or an increase due to compression or tension bending, respectively, of the paper cantilever substrate. The wind impacting onto the flexible paper substrate with negative and positive speeds resulted in a bending compression or tension that was related to the resistance measured from the sensor. It was demonstrated that the resistance of a 10-mm -ide line of the U-shaped graphite on the paper substrate was 24 kΩ at ∼ 40° and 45 kΩ at ∼− 40°. Furthermore, we found that the graphite patterned on paper substrate with a small line width, such as 3 mm, showed good linearity for the relationship between the measured resistance and the wind speed.

A primary challenge still exists in the field of thermoelectric generators (TEG) for practical applications in which a thermal system of the TEG is a crucial factor in TEG power generation. The material development for TEG has contributed significantly towards advancement in TEG applications over a decade, the need for a thermal system configuration is inevitable considering the applications. The thermal efficiency of TEG depends upon the temperature difference across its modules (between the hot and cold surfaces). Thermal design of the thermoelectric system is important to ensure that there exists a maximum temperature difference across the hot and cold surfaces of the TEG. Thermal Interface Material (TIM) in thermoelectric systems plays a main role in improving the efficiency of thermoelectric systems by reducing the temperature difference between the heat source and the hot surface of the TEG and similarly, the temperature difference between the cold surface of TEG and the heat sink. This review paper predominantly focuses on the thermal interfaces between the TEG modules which reduces the performance of a thermoelectric system. The characteristics of TIM in a TEG system (contact pressure, surface roughness and thermal conductivity) were analyzed with a mathematical model to emphasize the importance of TIM in a TEG system. This paper also highlights the existing challenges for Thermal Interface Materials in TEG applications and concludes with a brief discussion on future directions of TIM in TEG thermal systems.

This paper investigates solvent and concentration effects on photoluminescence (PL) or fluorescence properties of Rhodamine 800 (Rho800) dyes formed in aqueous solution and polymer thin-film. Various commonly used organic solvents including ethanol, methanol and cyclopentanol were studied at a constant dye concentration. There were small changes in the PL spectra for the different solvents in terms of PL intensity and peak wavelength. The highest PL intensity was observed for cyclopentanol and the lowest for ethanol. The longest peak wavelength was found in cyclopentanol (716 nm) and the shortest in methanol (708 nm). Dissolving the dye powder in the methanol solvent and varying the dye concentration in aqueous solution from the high concentrated solution to highly dilute states, the wavelength tunability was observed between about 700 nm in the dilute state and 730 nm at high concentration. Such a large shift may be attributed to the formation of dye aggregates. Rho800 dye-doped polyvinyl alcohol (PVA) polymer thin-film was further investigated. The PL intensity of the dye in the form of thin-film is lower than that of the aqueous solution form whereas the peak wavelength is redshifted due to the presence of PVA. This paper, to our best knowledge, reports the first study of spectroscopic properties of Rho800 dyes in various forms and provides useful guidelines for production of controllable organic luminescence sources.

Nanoscale devices are emerging as a platform for detecting biomolecules. Various issues were observed during the fabrication process such as random dopant fluctuation and thermal budget. To reduce these issues charge-plasma-based concept is introduced. This paper proposes the implementation of charge-plasma-based gate underlap dielectric modulated junctionless tunnel field effect transistor (DM-JLTFET) for the revelation of biomolecule immobilized in the open cavity gate channel region. In this p+ source and n+ drain regions are introduced by employing different work function over the intrinsic silicon. Also dual material gate architecture is implemented to reduce short channel effect without abandoning any other device characteristic. The sensitivity of biosensor is studied for both the neutral and charge-neutral biomolecules. The effect of device parameters such as channel thickness, cavity length and cavity thickness on drain current have been analyzed through simulations. This paper investigates the performance of charge-plasma-based gate underlap DM-JLTFET for biomolecule sensing applications while varying dielectric constant, charge density at different biasing conditions.

The effect of a room temperature curable dielectric ink (ZrSiO4) printed on commercial photo paper and prepared nanopaper on the dielectric properties at 2.4 GHz are studied. In both cases, the dielectric layer decreased the relative permittivity and dielectric loss and made the flexible substrates rigid. For the nanopaper, the permittivity decreased from 4.7 to 3.57 and the loss value from 0.12 to 0.04. The measured decreases for the photo paper were from 3.12 to 2.61 and from 0.09 to 0.05, respectively. In the performance of the simulated and fabricated inverted-F antennas, the effect of the dielectric layer could be observed in the decrease of its frequency with about 130 MHz mainly due to the thicker substrate. The measured total efficiency and gain were 83% and 3.4 dB. The proposed approach could be in the future used for further development of the antenna by modification of the dielectric ink with different additives.

There are many models for researching charge transport in semiconductors and improving their performance. Most of them give good descriptions of the experimental data at room temperature. But it is still an open question which model is correct. In this paper, numerical calculations based on three modified versions of a classical model were made, and compared with experimental data for typical devices at room or low temperatures. Although their results are very similar to each other at room temperatures, only the version considering exciton effects by using a hydrogen-like model can give qualitative descriptions to recent experimental data at low temperatures. Moreover, the mobility was researched in detail by comparing the constant model and temperature dependence model. Then, we found the performance increases with the mobility of each charge carrier type being independent to the mobility of the other one. This paper provides better insight into understanding the physical mechanism of carrier transport in semiconductors, and the results show that exciton effects should be considered in modeling organic solar cells.

With a body-centered tetragonal crystal structure, Sn grains were demonstrated to have highly anisotropic behaviors in various properties. The electromigration behavior of lead-free solder was impacted by the grain orientations. In this paper, the angle between the c-axis and the electron flow direction in composite solder joints (angle θ) was proven to be an important factor during electromigration. The effects of angle θ on the electromigration of composite solder joints were investigated in this paper. Cu particle-reinforced Sn3.5Ag solder joints were stressed under a current density of 104 A/cm2 at room temperature. After 336 h current stressing time, different electromigration phenomena occurred at the two sides of the grain boundary in the composite solder joint which contained two Sn grains with different angle θ. The Sn grains with the larger angle θ had a smaller growth rate of Cu6Sn5. In addition, a composite solder joint with a single Sn grain was set as the contrast and its angle θ was smaller than that of the composite solder joint with two Sn grains. The growth rate of Cu6Sn5 in the composite solder joint with a single grain was faster than that of the composite solder joint with two Sn grains.

In this paper, a regression model for evaluating the performance of solar concentrated thermoelectric generators (SCTEGs) is established and the significance of contributing parameters is discussed in detail. The model is based on several natural, design and operational parameters of the system, including the thermoelectric generator (TEG) module and its intrinsic material properties, the connected electrical load, concentrator attributes, heat transfer coefficients, solar flux, and ambient temperature. The model is developed by fitting a response curve, using the least-squares method, to the results. The sample points for the model were obtained by simulating a thermodynamic model, also developed in this paper, over a range of values of input variables. These samples were generated employing the Latin hypercube sampling (LHS) technique using a realistic distribution of parameters. The coefficient of determination was found to be 99.2%. The proposed model is validated by comparing the predicted results with those in the published literature. In addition, based on the elasticity for parameters in the model, sensitivity analysis was performed and the effects of parameters on the performance of SCTEGs are discussed in detail. This research will contribute to the design and performance evaluation of any SCTEG system for a variety of applications.

The objective of the present research work is to study the nonlinear optical properties of quaternary Se-Sn (Bi,Te) chalcogenide thin films. A Z-scan technique utilizing 800 nm femtosecond laser source has been used for the determination of the nonlinear refractive index (n 2), two-photon absorption coefficient (β 2) and third-order susceptibility (χ (3)). In the measurement of n 2, an aperture is placed in the far field before the detector (closed aperture), while for the measurement of β 2, entire transmitted light is collected by the detector without an aperture (open aperture). Self-focusing has been observed in closed aperture transmission spectra. The appearance of the peak after the valley in this spectrum reflects the positive nonlinear refractive index. The calculated value of n 2 of the studied thin films varies from 1.06 × 10−12 cm2/W to 0.88 × 10−12 cm2/W. The compound-dependent behavior of n 2 is explained in this paper. We have also compared the experimental values of n 2 with the theoretically determined values, other compounds of chalcogenide glass and pure silica. The n 2 of the investigated thin films is found to be 3200 times higher than pure silica. The results of the open aperture Z-scan revealed that the value of β 2 of the studied compound is in the order of 10−8 cm/W. The behavior of two-photon absorption is described by means of the optical band gap (E g) of the studied compound. The variation in the figure-of-merit from 0.32 to 1.4 with varying Sn content is also reported in this paper. The higher value of nonlinearity makes this material advantageous for optical fibers, waveguides and optical limiting devices.

This paper reports that a boron nitride nanotube (BNNT) mat containing air and 1.4 vol.% BNNTs is a low-k dielectric material for microelectronic packaging, exhibiting relative dielectric constant of 1.0 to 1.1 (50 Hz to 2 MHz) and elastic modulus of 10 MPa. The mat is prepared by compacting BNNTs at 5.8 kPa. This paper also presents measurements of the dielectric properties of BNNTs (mostly multiwalled). The relative dielectric constant of the BNNT solid in the mat decreases with increasing frequency, with attractively low values ranging from 3.0 to 6.2; the alternating-current (AC) electrical conductivity increases with increasing frequency, with attractively low values ranging from 10−10 S/m to 10−6 S/m and an approximately linear relationship between log conductivity and log frequency. The specific contact capacitance of the interface between BNNTs and the electrical contact decreases with increasing frequency, with attractively high values ranging from 1.6 μF/m2 to 2.3 μF/m2. The AC electrical resistivity of the BNNT–contact interface decreases with increasing frequency, with high values ranging from 0.14 MΩ cm2 to 440 MΩ cm2.

Gallium nitride (GaN)-on-diamond technology offers key parameters of high thermal conductivity, high power density, high electrical resistivity and small form factor at both the device and system levels, making GaN-on-diamond power amplifier devices very attractive for high-power radio-frequency (RF) applications, such as commercial base stations, satellite communications and defence applications. Current GaN-on-diamond integration technology involves either a diamond growth process or a diamond bonding process, both of which require precise interface engineering with appropriate interfacial layers. While such interfacial layers are of vital importance to make high-quality GaN-on-diamond integration possible, they also contribute to a large portion of the effective thermal boundary resistance (TBReff) at the interface, which has to be minimized to justify the benefit of GaN-on-diamond technology compared with the mainstream GaN on silicon carbide (SiC) technology. In this paper, we review the ongoing effort to develop interface engineering processes that position GaN-on-diamond as a promising technology for enabling the next generation of power devices.

In this paper, nanocrystalline Mg-ferrites have been synthesized by the low-cost sol-gel auto-combustion method using iron and magnesium nitrates as starting materials. The as-prepared sample was annealed at temperatures of 200°C, 400°C, 600°C, 800°C, and 1000°C in an air atmosphere to investigate the effect of annealing temperature on the physical properties. The structural and magnetic properties of the annealed ferrites were studied using x-ray diffraction, Fourier transform infrared (FTIR) and Raman spectroscopy, and vibrating-sample magnetometer. The crystalline size of the nano-crystallites increased from 12 nm to 51 nm with an increase in annealing temperature from 200°C to 1000°C. Raman spectroscopy measurements revealed the presence of a spinel structure where A1g and Eg modes occur along different bond lengths of Fe/Mg-O, due to different ionic radii of Mg+2 and Fe+3 ions. The two prominent vibration frequency peaks along different bond lengths for the cubic spinel materials were confirmed using the FTIR spectra. The saturation magnetization was found to increase from 0.71 μB/f.u. to 1.16 μB/f.u. with increasing annealing temperature from 200°C to 1000°C. The magnetization results show that the magnetic properties of the nanocrystalline Mg-ferrites improved with annealing temperature.

Composite supercapacitive materials can combine two different kinds of electrode materials with different energy storage mechanisms, as well as present enhanced supercapacitive performance. In this paper, a reduced graphene oxide aerogel (GA) was prepared with an adjustable pore structure and used as a matrix for loading of secondary active material (MnO2) through an electrochemical deposition method. The influences of the deposition time and deposition voltage on the electrochemical behaviors and specific capacitances of MnO2/GA composites were studied. The unique three-dimensional porous structure of GA can act as a good matrix for MnO2. The results show that when the deposition time is 30 s and deposition voltage is 1.0 V, the MnO2/GA composite has the highest specific capacitance of 664 F/g at a current density of 1 A/g. Compared with neat GA, the specific capacitance of the MnO2/GA composite is enhanced by 190%, which can be assigned to the co-contribution of two kinds of active materials, a facile ion diffusion path through the porous structure, and good electron conductivity of the GA.

Rechargeable aqueous zinc-ion hybrid supercapacitors and zinc-ion batteries are promising as safe energy storage systems because they combine the advantages of the high energy density of batteries and high power density of supercapacitor. This paper presents the elaboration of polyaniline (PANi)/Mn-Fe binary metal hydroxide (MnFe-BMH) composite cathode material and Zn anode for a Zn-ion hybrid supercapacitor (ZHSC) by electrochemistry. Two electrochemical techniques (voltage pulse and stepwise voltage) are carried out to perform different morphologies and structures of material modifying the cathode and anode electrodes. The ZHSC is packaged with a gel electrolyte solution of ZnSO4 1M and MnSO4 0.1M. Electrochemical performance of electrode materials and full-cell capacitors are studied by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements. The composite material for electrode modification has an outstanding specific capacitance of 470.3 F/g (167 Wh/kg) at a scan rate of 5 mV/s. Furthermore, this as-prepared electrode also shows excellent cycling stability with 94.6% capacity retention after 11,602 cycles. This demonstrates an improvement in endurance and energy density compared to the industrial SC electrodes.

In this paper, a tunable, broadband metamaterial (MM) bandpass filter based on three-dimensional (3D) structure was designed. It improves the out-of-band attenuation problem of the traditional planar metamaterial filters. The filter has good out-of-band attenuation and produces two transmission zeros at low and high frequencies. The transmission rates at the two transmission zeros are − 20.412 dB and − 16.705 dB, respectively. The simulated results show that the 3 dB bandwidth is 46.156 THz. In addition, due to the symmetry of the structure, it is insensitive to electromagnetic (EM) waves with different polarization. It can also adjust the working bandwidth, the transmission zero and the center frequency. In the process of adjustment, the working bandwidth remains basically unchanged, while the transmission zeros and center frequency stay linear. The structure we designed provides a great possibility for the application of metamaterial filters in optical frequency devices.

The present paper is focused on the structure, microstructure, and electrical properties of Ca (calcium)- and Dy (dysprosium)-doped ceria electrolyte materials. The CaDDC (Ce0.8Dy0.175Ca0.025O2-δ) sample was prepared through a modified sol–gel low-temperature process using sucrose and pectin. Rietveld analysis of powder x-ray diffraction (XRD) patterns confirms the cubic structure with a single phase. The Raman spectroscopy studies confirm the improved oxygen vacancies for the sample CaDDC over pure ceria. The scanning electron microscopy (SEM) images showed the highly dense surface. Energy-dispersive spectroscopy (EDS) confirms the sample chemical composition. Impedance spectroscopic studies were carried out to analyze the electrical properties. Migration energy (Em) and association energy (Easso.) were calculated from the dielectric relaxation process for oxide ion migration. Relaxation peaks were observed in tangent loss due to the presence of defect pairs. Modulus analysis showed a single relaxation peak, which indicates the reorientation of defect associates. The Ce0.8Dy0.175Ca0.025O2-δ sample exhibits improved conductivity of 1.23 × 10–2 S/cm at 600°C with an activation energy of 0.89 eV.

This paper presents a piezoelectric energy harvester with rotational magnetic excitation. Through the rotation of the rotating body, the intermittent magnetic force between the driving magnet and the tip magnetic mass drives the piezoelectric element to vibrate nonlinearly to generate electrical energy. The working principle and vibration model of the proposed energy harvester are studied theoretically and experimentally. With two driving magnets, 5-g tip magnetic mass, and 8-mm radial excitation distances, the piezoelectric energy harvester captures energy efficiently. The results demonstrate that the piezoelectric energy harvester produces three resonance frequencies of 5 Hz, 8 Hz, and 10 Hz. When the rotation frequency is 8 Hz, the maximum open-circuit voltages of the primary and auxiliary piezoelectric beam is 63.24 V and 30.38 V, respectively. The primary and auxiliary piezoelectric beam gets the maximum average power with external resistance is 125 KΩ and 75 KΩ, respectively. The maximum average power of the primary and auxiliary piezoelectric beam is 12.24 mW and 3.92 mW, respectively. At the maximum power of the primary and auxiliary piezoelectric beam, the voltage across the resistance is 39.12 V and 17.12 V, respectively.