Synthesis of nanometric LaCr0.5Mn0.5O3 perovskite at low temperature by the polyvinyl alcohol gel combustion method

Nanosized LaCr_0.5Mn_0.5O₃ perovskite was synthesised with relatively high surface area (15.5 m²/g) at low temperature (650 °C) by the combustion method using polyvinyl alcohol (PVA) and corresponding metal nitrates. The perovskite was characterised by X-ray diffraction, thermogravimetric and differential thermal analysis, field emission scanning electron microscopy and Brunauer–Emmett–Teller technique. The optimal preparative conditions were PVA/metals 3:1 by mole, pH = 3–4 and 80 °C for gel formation. Perovskite exhibits a good catalytic activity in total oxidation of m-xylene at the low temperature of reaction (250 °C).     

Experimental study of the organic light emitting diode with a p-type silicon anode

We have fabricated and studied an organic light emitting diode (OLED) with a p-type silicon anode and a SiO₂ buffer layer between the anode and the organic layers which emits light from a semitransparent top Yb/Au cathode. The luminance of the OLED is up to 5600 cd/m² at 17 V and 1800 mA/cm², the current efficiency is 0.31 cd/A. Both its luminance and current efficiency are much higher than those of the OLEDs with silicon as the anodes reported previously. The enhancement of the luminance and efficiency can be attributed to an improved balance between the hole- and electron-injection through two efficient ways: 1) restraining the hole-injection by inserting an ultra-thin SiO₂ buffer layer between the Si anode and the organic layers; and 2) enhancing the electron-injection by using a low work function, low optical reflectance and absorption semitransparent Yb/Au cathode.     

All‐Solution‐Processed Pure Formamidinium‐Based Perovskite Light‐Emitting Diodes

All‐solution‐processed pure formamidinium‐based perovskite light‐emitting diodes (PeLEDs) with record performance are successfully realized. It is found that the FAPbBr₃ device is hole dominant. To achieve charge carrier balance, on the anode side, PEDOT:PSS 8000 is employed as the hole injection layer, replacing PEDOT:PSS 4083 to suppress the hole current. On the cathode side, the solution‐processed ZnO nanoparticle (NP) is used as the electron injection layer in regular PeLEDs to improve the electron current. With the smallest ZnO NPs (2.9 nm) as electron injection layer (EIL), the solution‐processed PeLED exhibits a highest forward viewing power efficiency of 22.3 lm W^?1, a peak current efficiency of 21.3 cd A^?1, and an external quantum efficiency of 4.66%. The maximum brightness reaches a record 1.09 × 10⁵ cd m^?2. A record lifetime T₅₀ of 436 s is achieved at the initial brightness of 10 000 cd m^?2. Not only do PEDOT:PSS 8000 HIL and ZnO NPs EIL modulate the injected charge carriers to reach charge balance, but also they prevent the exciton quenching at the interface between the charge injection layer and the light emission layer. The subbandgap turn‐on voltage is attributed to Auger‐assisted energy up‐conversion process.     

Air‐Stable and High‐Performance Solution‐Processed Organic Light‐Emitting Devices Based on Hydrophobic Polymeric Ionic Liquid Carrier‐Injection Layers

A lot of research, mostly using electron‐injection layers (EILs) composed of alkali‐metal compounds has been reported with a view to increase the efficiency of solution‐processed organic light‐emitting devices (OLEDs). However, these materials have intractable properties, such as a strong affinity for moisture, which cause the degradation of OLEDs. Consequently, optimal EIL materials should exhibit high electron‐injection efficiency as well as be stable in air. In this study, polymer light‐emitting devices (PLEDs) based on the commonly used yellow‐fluorescence‐emitting polymer F8BT, which utilize poly(diallyldimethylammonium)‐based polymeric ionic liquids, are experimentally and analytically investigated. As a result, the optimized PLED employing an EIL comprising poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (poly(DDA)TFSI), which is expected to display good moisture resistance because of water repellency of fluorocarbon groups, exhibits excellent storage stability in air and electroluminescence performance with a low turn‐on voltage of 2.01 V, maximum external quantum efficiency of 9.00%, current efficiency of 30.1 cd A^?1, and power efficiency of 32.4 lm W^?1. The devices with poly(DDA)TFSI show one of the highest efficiencies as compared to the reported standard PLEDs. Moreover, poly(DDA)TFSI is applied as a hole‐injection layer (HIL). The optimized PLED using poly(DDA)TFSI as the HIL exhibits performances comparable to those of a device that uses a conventional poly(3,4‐ethylenedioxy‐thiophene):poly(4‐styrenesulfonate) HIL.     

Application of ultra-thin CdS film as buffer layer in non-doped blue organic light-emitting diodes

The device inserted 0.5 nm thick cadmium sulfide (CdS) as buffer layer, prepared by vacuum thermal evaporation method, has been studied on the non-doped blue organic light-emitting diode. Compared to the device without ultra-thin CdS film, the maximum luminance of the device with ultra-thin CdS film was 11,370 cd/m² at 11 V, and the maximum current efficiency reached 3.10 cd/A, increased 1.5 times and 1.2 times, respectively. In the optimized devices with the structure of ITO/MoO₃ (10 nm)/TPABBI (35 nm)/Bphen (40 nm)/CdS (0, 0.1, 0.3 and 0.5 nm)/LiF (0.5 nm)/Al (100 nm), the effects of CdS layer on the photoelectric performance of the devices were investigated in detail. When the CdS thickness was 0.3 nm, the maximum luminance was 13,590 cd/m² at 9 V and the turn on voltage was only 3 V. The maximum current efficiency of 3.42 cd/A was obtained. It is indicated that the simple structure of the device with inserted ultra-thin CdS film, cheap and stable inorganic photoelectric material, may be a promising way to fabricate hybrid organic–inorganic LEDs with high performances.     

Synthesis and optoelectronic properties of oxadiazole-functionalized iridium complexes in the poly(vinylcarbazole)-hosted devices

A class of oxadiazole-functionalized iridium complexes was used as phosphor emitters in poly (vinylcarbazole)-hosted devices. Efficient green electrophosphorescences were achieved in the devices with a maximum luminance efficiency of 9.3 cd/A at 10.6 mA/cm² and brightness of 3882 cd/m² at 92.1 mA/cm². More importantly, the iridium complexes-doped devices exhibited a low turn-on voltage of 7.0 V and an applied voltage of 9.2 V at 500 cd/m². The good optoelectronic properties of the complexes were attributed to the enhanced electron-injection and transport properties resulting from the effect of oxadiazole ligands in the complexes.     

Microstructure and thermoelectric properties of tungsten trioxide ceramics doped with a low amount of terbium dioxide

The effect of the nonstoichiometric compound terbium dioxide (Tb₄O₇) on the thermoelectric properties of tungsten trioxide (WO₃) ceramics was investigated. Among the sintered ceramics, the sample doped with 0.1 mol% Tb₄O₇ showed the maximum grain size and density. Doping with Tb₄O₇ also increased the electrical conductivity (σ) of the ceramics by about two orders of magnitude, and the sample doped with 0.1 mol% Tb₄O₇ showed the highest electrical conductivity. The absolute value of Seebeck coefficient (|S|) of the doped samples increased as well. Consequently, the power factor (σs ²) markedly increased. The sample doped with 2.0 mol% Tb₄O₇ demonstrated the maximum σs ² of 2.88 μW m^?1 K^?2 at 973 K, which was larger than the highest recorded σs ² for WO₃ ceramics (2.71 μW m^?1 K^?2 at 1,023 K). In addition, the low-doped sample (0.1 mol%) exhibited excellent thermoelectric properties.     

Effect of chromium carbide coating on thermal properties of short graphite fiber/Al composites

A chromium carbide coating was synthesized onto graphite fibers by molten salts method to improve the interfacial bonding and thermal properties of short graphite fiber/Al composites which were fabricated by vacuum pressure infiltration technique. The graphite fiber/Al composites with different thicknesses of chromium carbide coatings were prepared through varying plating times to investigate the influence of chromium carbide layer on the microstructures and thermal properties of the composites. The combined Maxwell–Garnett effective medium approach and acoustic mismatch model schemes were used to theoretically predict thermal conductivities of the composites. The results indicated that the chromium carbide coating formed on graphite fiber surface in molten salts consists mainly of the Cr₇C₃ phase. The Cr₇C₃-coating layer with plating time of 60 min and thickness of 0.5 μm was found to be most effective in improving the interfacial bonding and decreasing the interfacial thermal resistance between graphite fiber and aluminum matrix. The 40 vol% Cr₇C₃-coated graphite fiber/Al composite with Cr₇C₃ thickness of 0.5 μm exhibited 45.4 % enhancement in in-plane thermal conductivity of 221 W m^?1 K^?1 compared to that of uncoated composite, as well as the coefficient of thermal expansion of 9.4 × 10^?6 K^?1, which made it as very interesting material for thermal management applications.     

Lithium ion conducting solid polymer blend electrolyte based on bio-degradable polymers

Lithium ion conducting polymer blend electrolyte films based on poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) with different Mwt% of lithium nitrate (LiNO₃) salt, using a solution cast technique, have been prepared. The polymer blend electrolyte has been characterized by XRD, FTIR, DSC and impedance analyses. The XRD study reveals the amorphous nature of the polymer electrolyte. The FTIR study confirms the complex formation between the polymer and salt. The shifts in T _g values of 70 PVA–30 PVP blend and 70 PVA–30 PVP with different Mwt% of LiNO₃ electrolytes shown by DSC thermograms indicate an interaction between the polymer and the salt. The dependence of T _g and conductivity upon salt concentration has been discussed. The ion conductivity of the prepared polymer electrolyte has been found by a.c. impedance spectroscopic analysis. The PVA–PVP blend system with a composition of 70 wt% PVA: 30 wt% PVP exhibits the highest conductivity of 1·58 × 10^???6 Scm^???1 at room temperature. Polymer samples of 70 wt% PVA–30 wt% PVP blend with different molecular weight percentage of lithium nitrate with DMSO as solvent have been prepared and studied. High conductivity of 6·828 × 10^???4 Scm^???1 has been observed for the composition of 70 PVA:30 PVP:25 Mwt% of LiNO₃ with low activation energy 0·2673 eV. The conductivity is found to increase with increase in temperature. The temperature dependent conductivity of the polymer electrolyte follows the Arrhenius relationship which shows hopping of ions in the polymer matrix. The relaxation parameters (ω) and (τ) of the complexes have been calculated by using loss tangent spectra. The mechanical properties of polymer blend electrolyte such as tensile strength, elongation and degree of swelling have been measured and the results are presented.     

High-Voltage Aqueous Na-Ion Battery Enabled by Inert-Cation-Assisted Water-in-Salt Electrolyte

Water-in-salt (WiS) electrolytes provide a new pathway to widen the electrochemical window of aqueous electrolytes. However, their formulation strongly depends on the solubility of the chosen salts, imposing a stringent restriction on the number of possible WiS systems. This issue becomes more severe for aqueous Na-ion batteries (ANIBs) owing to the relatively lower solubility of sodium salts compared to its alkaline cousins (Li, K, and Cs). A new class of the inert-cation-assisted WiS (IC-WiS) electrolytes containing the tetraethylammonium (TEA⁺) inert cation is reported. The Na IC-WiS electrolyte at a superhigh concentration of 31 mol kg^–1 exhibits a wide electrochemical window of 3.3 V, suppresses transition metal dissolution from the cathode, and ensures singular intercalation of Na into both cathode and anode electrodes during cycling, which is often problematic in mixed alkali cation systems such as K–Na and Li–Na. Owing to these unique advantages of the IC-WiS electrolyte, the NaTiOPO₄ anode and Prussian blue analog Na_1.88Mn[Fe(CN)₆]_0.97·1.35H₂O cathode can be coupled to construct a full ANIB, delivering an average voltage of 1.74 V and a high energy density of 71 Wh kg⁻¹ with a capacity retention of 90% after 200 cycles at 0.25C and of 76% over 800 cycles at 1C.     

Efficiency and stability of polymer light-emitting diodes

The operation characteristics of polymer light-emitting diodes (PLEDs) are strongly dependent on materials, processing and the structure of the device. The device structure developed at Philips Research is presented together with some typical results for brightness, efficiency, response times and stability. The PLEDs typically operate at a voltage of 3–4 V for a brightness of 100 cd m^-2 and have an efficiency ranging from 2 cd A^-1 for orange emitting polymers (610 nm) up to 16 cd A^-1 for green emitting polymers (550 nm). The response time under conditions for display operation is determined by the charge carrier transport properties and amounts to 43 ns. Lifetimes of several thousand hours have been obtained for large orange emitting devices of 8 cm² for daylight visibility at room temperature.     

Drug release from heat-treated polyvinyl alcohol films

Abstract

Polyvinyl alcohol (PVA) films containing 10% w/w of a model drug, sulphathiazole, were cast from aqueous solutions and subjected to heat treatment at specific temperatures for known periods of time. Heat treatment at temperatures above the T_g of the PVA films slowed down the rate of drug release from the films. Increasing the temperature of heat treatment from 120°C to 160°C further decreased the rate of drug release. On the other hand, if the heat treatment were conducted at a temperature below the T_g e.g. at 80°C, there were insignificant differences between the release profile of sulphathiazole from heat-treated films and that from untreated films. The duration of heat treatment affected the rate of drug release to a smaller extent compared to the temperature of heat treatment. These results correlated with the heat induced changes in the morphology of, and in the extent of water uptake by the PVA films.     

Electron doping into the surface of SrTiO3 single crystal by using a field effect transistor structure having a polyvinyl alcohol gate insulator layer

We fabricated an n-channel accumulation-type field-effect transistor (FET) on a SrTiO₃ single crystal having a polyvinyl alcohol (PVA) layer and a Na⁺-doped PVA layer as a gate insulator. Both devices show an n-type FET performance having a response time of 10 - 100 second order. This slow response is due to the gradual formation of an electric double layer by solvated Na⁺ ions moving through the water absorbed in the PVA layer towards the surface of SrTiO₃ by applying a gate voltage (V_G), which is manifested by the fact that Na⁺-doping into the PVA layer dramatically reduces the driving voltages and the response time. In these devices, metallic or semiconducting behaviors are observed if the applied V_G is large enough to form a conducting channel during cooling of the devices. These results indicate that electrons are certainly doped into the surface of SrTiO₃ by applying V_G in both devices.     

Morphology, thermal, electrical and electrochemical stability of nano aluminium-oxide-filled polyvinyl alcohol composite gel electrolyte

In the present work, an attempt has been made to develop nano aluminium oxide (Al₂O₃)-filled polyvinyl alcohol (PVA) composite gel electrolytes. Surface morphological studies, thermal behaviour, electrochemical stability and electrical characterization of these composite gel electrolytes have been performed. An increase in the concentration of Al₂O₃ in composite gel electrolytes increases the amorphous characteristics of pure PVA. Bulk conductivity of composite gel electrolytes increases by an order of magnitude on addition of a nano filler. Maximum conductivity of 5·81 × 10^?2 S/cm is observed for 6 wt% Al₂O₃-filled polymer gel composite electrolytes. Temperature dependence of electrical conductivity shows a combination of Arrhenius and Vogel-Tamman-Fulcher (VTF) nature. Maximum current stability during oxidation and reduction cycle is noticed for 6 wt% Al₂O₃-filled PVA composite electrolyte, viz. ±1·65 V.     

Fabrication of Pt, Pt–Cu, and Pt–Sn nanofibers for direct ethanol protonic ceramic fuel cell application

Poly(vinyl pyrrolidone) with a M _w of 1.3 × 10⁶ g/mol (PVP) or 4 × 10⁴ g/mol (PVP_Low) was used as a polymer to fabricate PVP–Pt, PVP–Pt–Cu, and PVP_Low–Pt–Sn composite fibers by electrospinning. The effect of varying the electrospinning conditions on the fiber morphology was investigated, and the solution composition and electrospinning parameters were optimized to obtain composite fibers with a minimal bead formation. Pt, Pt–Cu, and Pt–Sn metal nanofibers were then obtained by heat treatment of the respective PVP–metal or PVP_Low–metal composite fibers at 300, 350, and 450 °C, respectively, in air for 5 h. Single cells of a direct ethanol protonic ceramic fuel cell were subsequently fabricated by applying the metal nanofibers, or a commercial Pt paste, as the anode on the surfaces of BaY_0.2Zr_0.8O_3?δ pellets and Pt paste as the cathode. The I–V polarization results showed that the metal nanofiber-based anode single cells provided higher maximum power densities than that of the Pt paste anode, with the Pt nanofiber-based anode single cell producing the highest maximum power density of 0.58 mW/cm² at 550 °C.     

Effects of transition metal (Cu,Zn, Mn) doped on leakage current and ferroelectric properties of BiFeO<Subscript>3</Subscript> thin films

BiFeO₃ (BFO) and transition metal (Cu, Zn, Mn) doped BFO thin films were successfully fabricated on indium tin oxide (ITO)/glass substrate using sol–gel process, spin coating and layer by layer technique. Compared to the pure BFO thin film, improved ferroelectric and leakage current properties were observed in the transition metal doped BFO thin films. The transition metal (Cu, Zn, Mn) doped BFO thin films have varying degrees of lower leakage current compared with the pure BFO film. The substitution of Cu and Zn increase the remnant polarization of BFO thin films. The values of remnant polarization (2Pr) were 120.6 and 126.7 μC/cm² at 933 kV/cm for Cu-doped and Zn-doped BFO thin film, respectively.     

Efficient white organic electroluminescent devices consisting of blue- and red-emitting layers

We report the fabrication and the characterization of white-organic-light-emitting devices consisting of a blue-emitting layer of 1,4-bis(2,2-diphenyl vinyl)benzene (DPVBi) and a red-emitting layer of 4-dicyanomethylene-2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-8-yl)vinyl]-4H-pyran (DCM2) doped into either 4,4′bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (α-NPD) or tris(8-hydroxyquinoline) aluminum (Alq₃). The spectral emission depends on both the doping location of DCM2 and its doping concentration. The electroluminescence (EL) spectra consist of two broad bands around 460 nm (DPVBi) and 560 nm (α-NPD:DCM2) or 590 nm (Alq₃:DCM2). We obtained an efficient white-light emission from the devices with the 0.2% DCM2 doping in α-NPD layer. The device shows the CIE coordinates of (0.33, 0.36), an external quantum efficiency (QE) of about 3.1%, and a luminous efficiency of 3.75 lm/W at luminance 100 cd/m². The maximum luminance of about 41,000 cd/m² was obtained.     

Composition optimization of extruded starch foams using response surface methodology

Response surface methodology (RSM) was used to analyse the effect of polyvinyl alcohol (PVA) and calcium carbonate (CaCO₃) on the objective attributes (shipping bulk density, radial expansion ratio, compressibility and spring index) of a biodegradable cushioning extrudate. A rotatable central composite design (CCD) was used to develop models for the objective responses. The experiments were run at 105°C with a feed rate of 27.8 l/h, screw speed 500 r.p.m. and die diameter 3.92 mm. Responses were most affected by changes in polyvinyl alcohol (PVA) levels and to a lesser extent by calcium carbonate (CaCO₃) levels. Individual contour plots of the different responses were overlaid, and regions meeting the optimum shipping bulk density of 6.00 kg/m³, radial expansion ratio of 3.30, compressibility of 43.71 N, and spring index of 0.91 were identified at the PVA level of 20.23% and the CaCO₃ level of 7.89%, respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

Studies on structural,electrical and dielectric properties of nickel ion conducting polyvinyl alcohol based polymer electrolyte films

Polyvinyl alcohol (PVA) complexed with different weight percent ratios of Nickel Bromide (NiBr₂) salt were prepared by using solution cast technique. X-ray diffraction analysis confirmed the complexation of the salt with the polymer. Differential scanning calorimetry was used to determine the glass transition and melting temperatures of pure PVA and PVA:NiBr₂ complexed films. Electrical conductivity was measured using ac impedance analyzer in the frequency and temperature range 1 Hz–1 MHz and 303–373 K respectively. It was observed that the magnitude of electrical conductivity increases with NiBr₂ salt concentration as well as temperature. Frequency dependence electrical conductivity of the complexed polymer electrolyte films follows the Jonscher’s equation. The dielectric behavior was analyzed using dielectric permittivity\(\left( {{\varepsilon ^\prime}} \right)\) and loss tangent \(\left( {\tan \delta } \right)\) of the samples. Relaxation time was determined from the variation of loss tangent with frequency at different temperatures. The modulus spectra indicated the non-Debye nature of the material.     

Improved cycling stability of the capping agent-free nanocrystalline FeS<Subscript>2</Subscript> cathode via an upper cut-off voltage control

Transition metal chalcogenides such as FeS₂ are promising electrode materials for energy storage. However, poor rate performance and low cycling stability hinder the practical application of FeS₂ cathode in secondary batteries. In this study, highly pure pyrite FeS₂ nanocrystals (NCs) with octahedral shape and 200–300 nm size have been synthesized via a facile and environmentally benign approach based on a surfactant-free aqueous reaction. Combined with a compatible ether electrolyte, the prepared FeS₂ NCs, despite their dimension far beyond the quantum confined regime, could achieve high utilization and reversibility as a cathode active material due to the well-defined crystal structure and the uncapped rough surfaces. Furthermore, we find that the last charging voltage step of FeS₂ only contributes a minor capacity but caused severe capacity fading due to the formation of soluble polysulfides. By suppressing this step through setting a proper upper cut-off voltage, the cycle life of the Li/FeS₂ cell is dramatically improved. The Li/FeS₂ cell running over a voltage window of 1.0–2.4 V at 1C delivers an initial capacity of 486.1 mA h g^?1, slightly lower than that running over 1.0–3.0 V (561.1 mA h g^?1), but outperforms the latter substantially after 500 cycles (367 mA h g^?1 vs 315 mA h g^?1), corresponding to a capacity decay rate as low as 0.048% per cycle. Our results provide a meaningful approach for the development of not only the advanced FeS₂ material for long-life rechargeable batteries, but also other transition metal chalcogenide nanomaterials for a variety of potential applications.