IET Nanodielectrics最新文献

The authors demonstrate how a simple step of loading an electrochromically active Prussian blue (PB; an ionic solid) electrode with Li⁺ ions can help in achieving a more efficient viologen based solid state hybrid electrochromic device. To accomplish this, two different devices, with and without Li⁺ ion loaded PB electrodes, have been fabricated. These devices have been compared in terms of their current-voltage response, bias dependent optical modulation and corresponding colour switching to establish the role of Li⁺ ion in charge transport and charge balancing involved during bias induced redox mediated colour switching of the two devices. The Li⁺ containing PB electrode device exhibits a superior performance with twice (40%) the value of colour contrast (20%), quick response switching (1.3 s), excellent stability (8400 s) and better power efficiency as compared to the device containing as-synthesised PB electrode. A mechanism has been proposed to explain the role of the Li⁺ ion which is later substantiated using bias-dependent in situ Raman spectroscopic evidences.

Dielectric materials with high-energy-density and low-energy-loss have received lot of attention in terms of renewable energy storage and application. PVDF-based polymer/ceramics composite dielectrics are considered as one of the most promising materials due to their high dielectric constant. However, the high remnant polarisation (P_r) of ferroelectric polymer matrix and ceramics fillers generates a lot of energy loss and residual heat during charge-discharge cycles, which limits their practical applications. Compared with ferroelectrics, relaxor ferroelectric and antiferroelectric dielectrics may have high energy efficiency due to their lower P_r. Here, the relaxor ferroelectric matrix and antiferroelectric filler coated by the polydopamine layer were prepared by chemical grafting and solid-state method, respectively. Afterwards, the P(VDF-TrFE-CTFE)-g-PMMA/PLZST nanocomposite was prepared via solution casting. Experimental results show that the energy loss of the optimised nanocomposites was significantly reduced, leading to an enhanced charge-discharge efficiency (η) of 78% at 450 MV/m, which is 267% of the pure P(VDF-TrFE-CTFE) matrix and superior to those of most polymer/ferroelectric filler nanocomposites. It is encouraging that the breakdown strength and energy storage density of the P(VDF-TrFE-CTFE)-g-PMMA/PLZST nanocomposites with 6 wt% filler fractions reach the values of 458 MV/m and 10.3 J/cm³. This study establishes a simple and effective strategy for preparing capacitors with high energy efficiency.

A nanostructured film of NiCo₂O₄ has been prepared using a hydrothermal technique by simply using separate precursors to obtain nanoneedle-like architecture for electrochromic applications. A homogeneous film consisting of packed nanoneedles with moderate density, appearing translucent white in colour, has been obtained and characterized using XRD and Raman spectroscopy techniques for confirming the composition and structure. Electrochemical analysis of the film reveals that the film shows good electrochromic properties under the anodic scan of potential with strong stability. The mechanism of the electrode under the transformation from natural white to opaque dark brown colour has been understood with the help of an in situ optical absorption spectroscopy technique. The electrode is found electrochromically active with a bias of up to 2 V and shows 50% optical contrast which makes it a good candidate for application in a solid state electrochromic device.

This work presents a new approach for the design of an FMF with a Gaussian core and a trench in the cladding. For the proposed few-mode fibre (FMF), Fused Silica (SiO₂) is considered as a host-material, whereas Germanium Oxide(GeO₂) and Fluorine(F)are taken as the dopant for large data transmission. The mole percentages of the dopant material along with the fibre profile parameters are varied to achieve 10 linearly polarized (LP) modes through the proposed FMF. The proposed FMF structure is tested and verified through simulated experiments. The results indicate the proposed FMF structure with the mole percentage 11.5% of GeO₂, 2% of F, and the normalized full-width-half-maximum (FWHM) of the core in the range of 4 to 10 supports 10 LP modes in the order of LP₀₁, LP₁₁, LP₂₁, LP₀₂, LP₃₁, LP₁₂, LP₄₁, LP₂₂, LP₀₃, and LP₅₁. The effective index difference (Δn_eff) between the adjacent LP modes is maintained greater than $��1�\times �{10}^{�-�3�}�$ and a weakly coupled 10x10 Gbps SDM transmission link is established through intensity-modulation and direct-detection (IM/DD) using the proposed Gaussian core-FMF. The link performance is analysed, verified and an acceptable bit-error-rate (BER) of 10⁻²⁰ is achieved over 50 km without amplifiers.

An electret-based electrostatic energy harvester featuring tuneable resonance frequency, small size, light weight, and high output power was designed and its performance predicted by the finite element method and verified by experiment. The device consists of a resilient fluorinated polyethylene propylene (FEP) electret film that is metallised on one side with a small seismic mass attached to its centre and an arc-shaped counter electrode. In principle, such an energy harvester is mechanically a mass-spring system and electrically a self-bias voltage variable capacitor and converts vibrational energy into electrical energy by electromechanical coupling. For an energy harvester sample with dimensions of 30 × 10 × 9 mm for which the last dimension denotes the initial depth of the centre of the harvester, the resonance frequency can be tuned from 17 to 70 Hz by stretching the length of the FEP film loaded with a given seismic mass of 0.06 g. For a seismic mass of 0.1 g, the harvester generated a power up to 797 μW to a matching resistor at its resonance frequency of 17 Hz at an acceleration of 1×g, where g is the gravity of the earth. Such energy harvesters are promising candidates for use in self-powered electronic devices and wireless sensor network nodes.

The authors report the key findings from an experimental study that explored the use of activated bentonite for the reclamation of thermally aged ester-based transformer nanofluids to improve their insulation performance. Bentonite activated with acid treatment caused an increase in the specific surface area and pore volume of bentonite compared to the bentonite sample before treatment, thus imparting an improved adsorption capability. Physico-chemical diagnostic studies were carried out to characterise the activated bentonite. The insulation performance of the reclaimed natural ester and nano-filled ester fluid samples was assessed by measuring the corona inception voltage and breakdown voltage of each fluid sample, apart form measuring the flow electrification current using the spinning disk method. The results revealed that the reclamation process improved the corona inception voltage, dissipation factor and the breakdown voltage of the base ester fluid sample due to attraction of carbon particles to activated bentonite, but no significant variation was observed with nanofluids due to the depletion of the electrical double layer. The flow electrification current of ester and ester nanofluids reduced after treatment with activated bentonite, may be attributed to the interaction between copper and bentonite that alters the double layer formation responsible for the separation of charges.

Nanoparticles of Ni_0.5Co_0.2Zn_0.3Fe₂O₄ were prepared using the sol-gel combustion route. The nanoparticles were characterised by x-ray diffraction to confirm single-phase formation in a cubic spinel structure. Micro- and nanostructural analyses were carried out using field emission-scanning electron microscopy and field emission-transmission electron microscopy, respectively. A planetary ball milling technique was used to grind the powder into nanoparticles; the average particle size was 64 nm. Energy-dispersive X-ray spectroscopy was used to determine the atomic composition of the sample. Radio-frequency characteristics were recorded for dielectric measurement in a frequency range of 1 Hz to 15 MHz using a broadband dielectric spectrometer. Terahertz (THz) time-domain spectroscopy was performed to study THz-optical parameters such as refractive index, dielectric constant, and conductivity at room temperature in a frequency range of 0.3−2.2 THz using an indigenously developed THz time-domain spectroscopy setup. The magnetic properties of the sample were studied using a SQUID vibrating sample magnetometer under an applied magnetic field of ±10 kOe. An examination of M-H loops revealed that the saturation magnetization $��\left(�M_s�\right)�$, remanent magnetization $��\left(�M_r�\right)�$ and coercivity $��\left(�H_c�\right)�$ increased with an increase in temperature from 300 to 50 K.

The synthesis of core@double-shells structured TiO₂@C@SiO₂ nanowires (NWs) with variable thickness of carbon inner shell and SiO₂ outer shell was achieved by individually controlling the chemical vapour deposition time and amount of silicon precursor added in the sol–gel synthesis. The resultant TiO₂@C@SiO₂ NWs filled nanocomposites exhibited an excellent dielectric performance with simultaneously improved dielectric constant and suppressed dielectric loss, which could be further regulated by individually controlling the carbon inner shell and SiO₂ outer shell thickness. More importantly, the influences of the conductive carbon inner shell and insulated SiO₂ outer shell thickness on the dielectric performance of nanocomposites were clearly revealed. The increase of the conductive carbon inner shell thickness would lead to an increase in dielectric constant and loss of nanocomposites, while the insulated SiO₂ outer shell exhibited a totally opposite law that the dielectric constant and loss of nanocomposites decrease with increasing SiO₂ outer shell thickness. Numerical simulations were also carried out to theoretically verify the relationship between the dielectric loss and SiO₂ outer shell thickness. This promising controllable multi-shell structure could be extended to a variety of hybrids to develop high-performance dielectric nanocomposites.

Avalanche photodiode (APD) is an indispensable receiver component because of its high bandwidth and low noise performance. Recently, APD reliability, under harsh environmental stresses such as high heat and humidity, has drawn great interest in the applications of passive optical network, wireless, military, and free space optics. The authors study the APD degradation under the harsh environment of high humidity and high bias. The failure morphology through cross-sectional scanning electron microscopy is shown, and a new moisture degradation model based on electrochemical oxidation to account for the failure mechanism is developed.