Direct current bias studies on (Bi2O3)0.8(Er2O3)0.2 electrolyte and Ag–(Bi2O3)0.8(Er2O3)0.2 cermet electrode

20 mol% erbia stabilized bismuth oxide (ESB) in the cubic fluorite structure is one of the highest oxygen ion conductors known. On annealing at temperatures below the transition temperature (∼600 °C), a fast continuous decay in oxygen ion conductivity occurs which has been attributed to the occupational and positional ordering on the oxygen ion sublattice. The reverse transition is characterized by the enthalpy required to disorder the ordered lattice. This study looked into the effect of direct current bias on the ordering kinetics of ESB solid electrolytes using symmetrical cells consisting of Ag–ESB cermet electrodes. Electrochemical impedance spectroscopy studies showed that on isothermal annealing at 500 °C, the current bias does not have a significant effect on the conductivity decay, though the differential scanning calorimetry (DSC) studies showed that under bias the endotherm related with the reverse transition appeared at shorter annealing time periods. Ag–ESB electrodes showed good performance, though were unstable at 625 °C under higher bias currents due to the Ag electromigration along with the oxygen flux.     

Study of phase transition of TiO<Subscript>2</Subscript>–CaO system

Electrical conductivity of TiO₂ doped with CaO has been measured at different temperatures for various molar ratios. The conductivity after initially remaining constant till about 140 °C increases with temperature due to the migration of vacancies created by doping. After attaining a maximum value at 240 °C, conductivity decreases due to the collapse of fluorite framework. A second rise in conductivity at high temperature beyond 400 °C indicates the phase transition of TiO₂, from anatase to rutile, which is confirmed by the differential scanning calorimetry results. X-ray powder diffraction, impedance measurements, and Fourier transform infrared spectral studies were also carried out for confirming the doping effect and phase transitions in TiO₂. Doping of TiO₂ with CaO shifts the transition to lower temperatures.     

Ac-conductivity and dielectric relaxations above glass transition temperature for parylene-C thin films

45% semi-crystalline parylene-C (–H₂C–C₆H₃Cl–CH₂–) _n thin films (5.8 μm) polymers have been investigated by broadband dielectric spectroscopy for temperatures above the glass transition (T _g =90°C). Good insulating properties of parylene-C were obtained until operating temperatures as high as 200°C. Thus, low-frequency conductivities from 10⁻¹⁵ to 10⁻¹² S/cm were obtained for temperatures varying from 90 to 185°C, respectively. This conductivity is at the origin of a significant increase in the dielectric constant at low frequency and at high temperature. As a consequence, Maxwell–Wagner–Sillars (MWS) polarization at the amorphous/crystalline interfaces is put in evidence with activation energy of 1.5 eV. Coupled TGA (Thermogravimetric analysis) and DTA (differential thermal analysis) revealed that the material is stable up to 400°C. This is particularly interesting to integrate this material for new applications as organic field effect transistors (OFETs). Electric conductivity measured at temperatures up to 200°C obeys to the well-known Jonscher law. The plateau observed in the low frequency part of this conductivity is temperature-dependent and follows Arrhenius behavior with activation energy of 0.97 eV (deep traps).     

Synthesis,deposition and characterization of tin selenide thin films by thermal evaporation technique

Tin selenide alloy was synthesized by following simple chemical reaction method, at comparatively lower temperature of 100 °C, from alkaline medium using SnCl₂.2H₂O and selenium as source materials. Powder X-ray diffraction analysis reveals that the particle size of the synthesized product is in nanometer scale. Using the reaction product as source material, the SnSe films were deposited on glass substrates at room temperature, 150 °C, 250 °C, 350 °C and 450 °C. Structural, elemental, optical, surface morphological and electrical properties of the as deposited films were studied by X-ray diffraction, Energy Dispersive X-ray Analysis, UV-Vis-NIR, Scanning Electron Microscopy and Hall effect measurement techniques and the relevant details have been obtained.     

High-temperature proton conductivity in acceptor-doped LaNbO4

The conductivity of acceptor-doped LaNbO₄ has been investigated in the temperature range 300 to 1200 °C as a function of the oxygen pressure and water vapor pressure by means of impedance spectroscopy and EMF measurements. The conductivity is predominantly ionic below 800 °C in air and for higher temperatures under reducing conditions. Protons are the major ionic charge carrier in the presence of water vapor. A maximum in proton conductivity of ∼ 0.001 S/cm was obtained at 950 °C in atmospheres containing ca 2% H₂O. At high temperatures (> 1000 °C) under oxidizing conditions, electron hole conduction prevails. The conductivity has been modeled assuming that oxygen vacancies and protons compensate the acceptor doping. Transport coefficients describing mobility of defects and thermodynamic constants for the incorporation of protons have been derived.     

Effect on ion dissociation in MWCNT-based polymer nanocomposite

Polymer nanocomposite has been proven to improve the property of polymer salt complex. Organo-modified clay and inorganic oxides are the most commonly used filler for polymer nanocomposite (PNC). However, single wall carbon nanotube (SWCNT)/multiwall carbon nanotube (MWCNT) are becoming popular filler for PNC for their high surface area and high mechanical stability. In this work, a series of PNC sample has been prepared by using polyethylene oxide (PEO)-polydimethylsiloxane (PDMS) blend as polymer matrix, an optimized salt stoichiometry of Ö/Li ~15, and surface-modified MWCNT as filler. The effect of ion-polymer and ion-MWCNT interaction in the polymer nanocomposite has been investigated by using XRD, SEM, FTIR, and electrical study. X-ray diffraction pattern confirms the dispersion of MWCNT inside the polymer chain and modifies the structural parameter of the polymer matrix. FTIR spectra indicate inclusion of MWCNT inside the polymer salt complex which changes the ion dissociation/association in the polymer host matrix. Further, the changes in structural, thermal, and electrical property of the polymer salt complex system have been studied by using SEM, DSC, and impedance analysis. Dc conductivity study shows that optimized PNC sample has conductivity of 8.04 × 10⁻⁵ S cm⁻¹. This is almost two order enhancement from pure polymer salt system (10⁻⁶ S cm⁻¹).

     

Effect of temperature on the hybrid supercapacitor based on NiO and activated carbon with alkaline polymer gel electrolyte

A hybrid supercapacitor was fabricated with NiO and activated carbon as positive and negative electrode, PVA–KOH–H₂O containing 5 M KOH as alkaline polymer gel electrolyte, respectively. Cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements were applied to investigate the dependence of the hybrid supercapacitor on the temperatures from − 20 to 40 °C. The results demonstrated that the capacitive performance of the hybrid supercapacitor turned even better with the temperatures rising up from − 20 to 40 °C. The increase of temperature improved the conductivity of the alkaline polymer gel electrolyte, decreased the charge-transfer resistance and made the better contact at the interface between the electroactive materials and the alkaline gel electrolyte at higher operating temperature. The maximum of the specific capacitance and energy density of the hybrid supercapacitor were 73.4 F/g and 26.1 Wh/kg at the current density of 0.1 A/g and the operating temperature of 40 °C, respectively.     

Studies on PEO-based sodium ion conducting composite polymer films

A sodium ion conducting composite polymer electrolyte (CPE) prepared by solution-caste technique by dispersion of an electrochemically inert ceramic filler (SnO₂) in the PEO–salt complex matrix is reported. The effect of filler concentration on morphological, electrical, electrochemical, and mechanical stability of the CPE films has been investigated and analyzed. Composite nature of the films has been confirmed from X-ray diffraction and scanning electron microscopy patterns. Room temperature d.c. conductivity observed as a function of filler concentration indicates an enhancement (maximum) at 1–2 wt% filler concentration followed by another maximum at ∼10 wt% SnO₂. This two-maxima feature of electrical conductivity as a function of filler concentration remains unaltered in the CPE films even at 100 °C (i.e., after crystalline melting), suggesting an active role of the filler particles in governing electrical transport. Substantial enhancement in the voltage stability and mechanical properties of the CPE films has been noticed on filler dispersion. The composite polymer films have been observed to be predominantly ionic in nature with t _ion ∼ 0.99 for 1–2 wt% SnO₂. However, this value gets lowered on increasing addition of SnO₂ with t _ion ∼ 0.90 for 25 wt% SnO₂. A calculation of ionic and electronic conductivity for 25 wt% of SnO₂ film works out to be ∼2.34 × 10⁻⁶ and 2.6 × 10⁻⁷ S/cm, respectively.     

Growth and characterization of l-histidine cadmium chloride monohydrate a semiorganic nonlinear optical crystals

l-histidine cadmium chloride monohydrate (LHCCM), a semiorganic nonlinear optical material was grown from aqueous solution by slow solvent evaporation method at room temperature. The LHCCM crystals were characterized by X-ray powder diffraction analysis. The presence of functional groups was identified through fourier transform infrared spectroscopy. Thermogravimetric and differential thermal analysis confirms that the crystal is stable up to 277 °C. The dielectric constant was studied as a function of frequency for various temperatures. The mechanical properties of the grown crystals have been studied using Vickers microhardness tester. The second harmonic generation behavior of LHCCM crystal was tested by modified Kurtz–Perry powder technique.     

Structural and dielectric properties of Ba3V2O8 ceramics

Polycrystalline sample of Ba₃V₂O₈ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction (XRD) analysis confirms the formation of single-phase compound of hexagonal (rhombohedral) crystal structure at room temperature. Microstructural analysis by scanning electron microscope (SEM) shows that the compound has well defined grains, which are distributed uniformly throughout the surface of the sample. The dielectric properties of the compound studied in a wide frequency range (10²–10⁶ Hz) at different temperatures (25–400 °C), exhibits that they are temperature dependent. Detailed analysis of impedance spectra showed that the electric properties of the material are strongly dependent on frequency and temperature. The activation energy, calculated from the temperature dependence of ac conductivity (dielectric data), was found to be 0.23 eV at 50 kHz in the higher temperature region.     

Impedance spectroscopy and dielectric analysis in KH2PO4 single crystal

Optical observation, differential scanning calorimetry, thermogravimetric analysis, and differential thermogravimetric measurements have been carried out on KH₂PO₄ single crystals. As compared with the optical observation of crystal under polarizing microscope, the dehydration process occurred gradually over the crystal surface at temperatures above 195 °C and then the interior of the sample. The ac impedance measurements were performed as a function of both frequency and temperature. The electrical conduction and dielectric relaxation have been studied. The activation energy of migration is 1.02 eV in the temperature range between 150 and 179 °C. The conduction mechanism in this temperature range is attributed to the hopping of proton among hydrogen vacancies. At temperatures above 186 °C, a higher conductivity activation energy with 2.94 eV is obtained. In addition to the proton conduction, the migration of the heavier ions (such as potassium ion) is also suggested.     

Green synthesis of silver-graphene nanocomposite-based transparent conducting film

In the present work, silver nanoparticles (Ag NPs)/graphene nanocomposite has been synthesized successfully by simple solvothermal method via green route. Citric acid is used as green reducing agent for the reduction of graphene oxide (GO) and Ag ions. Silver nitrate is used as a precursor material for Ag NPs. As synthesized Ag NPs/graphene nanocomposite has been characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infra-red spectroscopy, UV–vis spectroscopy, thermal gravimetric analysis, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. Experimental results confirm the reduction of GO and the successful formation of Ag NPs decorated graphene nanosheets. In addition, spray coating technique is employed for the fabrication of transparent conducting films. Enhancement in the optoelectrical signatures has been achieved using thermal graphitization of fabricated films. Thermal graphitization at 800 °C for 1 h marks the best performance of fabricated film with sheet resistance of ~3.4 kΩ/□ and transmittance (550 nm) of ~66.40%, respectively.     

Effects of inert fillers on the mechanical and electrochemical properties of lithium salt-poly(ethylene oxide) polymer electrolytes

The effects of adding an inert filler (α-alumina) to lithium perchlorate-poly(ethylene oxide) polymer electrolytes have been investigated. It was found that additions of 10 vol. % α-alumina had a negligible effect on the ionic conductivity of the polymer but gave a significant improvement in the mechanical stability of the material at temperatures in excess of 100°C. A.C. measurements on samples containing 0 and 10 vol. % α-alumina gave values of 0.2 to 0.3 for the transport number of the lithium ions between 110 and 130°C.     

Thermal conductivity of high-porosity biocarbon preforms of beech wood

This paper reports on measurements performed in the temperature range 5–300 K for the thermal conductivity κ and electrical resistivity ρ of high-porosity (cellular pores) biocarbon preforms prepared by pyrolysis (carbonization) of beech wood in an argon flow at carbonization temperatures of 1000 and 2400°C. X-ray structure analysis of the samples has been performed at 300 K. The samples have revealed the presence of nanocrystallites making up the carbon matrices of these biocarbon preforms. Their size has been determined. For samples prepared at T _carb = 1000 and 2400°C, the nanocrystallite sizes are found to be in the ranges 12–25 and 28–60 κ(T) are determined for the samples cut along and across the tree growth direction. The thermal conductivity κ increases with increasing carbonization temperature and nanocrystallite size in the carbon matrix of the sample. Thermal conductivity measurements conducted on samples of both types have revealed an unusual temperature dependence of the phonon thermal conductivity for amorphous materials. As the temperature increases from 5 to 300 K, it first increases in proportion to T, to transfer subsequently to ∼T ^1.5 scaling. The results obtained are analyzed.     

Analysis of phase transition behavior of BaCeO3 with thermal analyses and high temperature X-ray diffraction

Structural phase transitions in BaCeO₃ have been investigated with combination of differential scanning calorimetry (DSC), dilatometry and high temperature X-ray diffraction with high sensitivity and resolution. In DSC curve at heating procedures, baseline shift, endothermic peak and another baseline shift were observed at 260 °C, 385 °C and 895 °C, respectively. From DSC curve at cooling procedure, it was revealed that all the baseline shifts and peak were reversible. No hysteresis was observed in the both baseline shifts indicating second order phase transition at 260 °C and 895 °C with variation of specific heat capacity, ΔC_p, of 10 J/mol K and 7 J/mol K, respectively; whereas the order of the phase transition at 385 °C was revealed to be the first since hysteresis was detected around 370–385 °C. Variation of enthalpy, ΔH, at the phase transition was 45 J/mol. High temperature X-ray diffraction measurements have revealed that the crystal structure of BaCeO₃ changes from primitive orthorhombic perovskite through body-centered one, rhombohedral distorted one to cubic one around 280 °C, 400 °C and 900 °C, showing correspondence with DSC curves. Dependence of molar volume on temperature estimated from high temperature X-ray diffraction showed agreement with thermal expansion behavior observed with dilatometry.     

Silver-induced activation for improving the electrical characteristics of GaN-based vertical light-emitting diodes

Silver (Ag) contacts are important reflectors for vertical-structure GaN-based light-emitting diodes (LEDs). The Ag contacts produce good electrical and optical properties at different annealing temperatures. Thus, in order to best optimize the reliability of LEDs, we introduced an Ag activation process before performing normal annealing treatments. In other words, after removing 200-nm-thick Ag layers on p-GaN that were annealed at 500 °C for 1 min, Ag films were deposited on the Ag-activated p-GaN, which were subsequently annealed at 300 °C for 1 min. The activated LEDs fabricated with the 300 °C-annealed Ag contacts reveal better electrical properties than the reference LEDs. For example, the activated LEDs give a forward voltage of 2.92 V at an injection current of 20 mA, whereas the reference LEDs with the 300- and 500 °C-annealed Ag contacts yield 3.02 and 2.98 V at 20 mA, respectively. The activated LEDs yield 4.9% and 17% higher output power (at 30 mW) than the reference LEDs with the Ag contacts annealed at 300 and 500 °C. The activation-induced electrical improvement is briefly described and discussed.     

Enhanced blue photoluminescence and new crystallinity of Ag/organic rubrene core-shell nanoparticles through hydrothermal treatment

Light-emitting organic semiconductors have attracted considerable attention for the nanoscale fabrication of organic-based displays and their potential application in optoelectronics, plasmonics, and photonics. In this study, core-shell hybrid nanostructures of organic rubrene coated on Ag nanoparticles (NPs) have been synthesized using a chemical reduction method. The thickness of the rubrene shell was 2.6–6.0 nm and the diameter of the Ag core was 30–70 nm. The optical and structural properties of the Ag/rubrene core-shell NPs were tuned by hydrothermal (HT) treatment at 190 °C. The Ag/rubrene core-shell NPs were characterized by high-resolution transmission electron microscopy and energy-dispersive X-ray (EDX) spectroscopy before and after the HT treatment, and their structural properties were confirmed through X-ray diffraction (XRD) analysis. XRD peaks related to an orthorhombic phase were observed along with the original triclinic crystal structure of the rubrene shell, and the triclinic crystal domain size increased from 28.2 nm to 30.8 nm owing to the HT treatment. Interestingly, the green light emission (λ_em = 550 nm) of the Ag/rubrene core-shell NPs changed to blue light emission (λ_em = 425 nm), increasing in intensity through the HT treatment. This is caused by the crystal change with H-type aggregation and enhanced energy transfer from a surface plasmon resonance.     

Properties of Bi2O3 thin films prepared via a modified Pechini route

Thin bismuth oxide films have been prepared by a modified Pechini route on glass substrate and annealed at temperatures ranging between 400 °C and 700 °C using bismuth nitrate as raw material. The thin films were then characterized for structural, surface morphological, optical and electrical properties by means of X-ray diffraction (XRD), Atomic force microscopy (AFM), scanning electron microscopy (SEM), optical absorption and d.c. two-probe, respectively. Structural investigations indicated that as-prepared bismuth oxide films were polycrystalline and multiphase, and annealing temperatures played a key role in the composition and optical properties of these films. AFM and SEM images revealed well defined particles which are highly influenced by annealing temperatures. The optical studies showed a direct band gap which varied with annealing temperatures between 3.63 eV and 3.74 eV. The electrical measurement showed that the electrical resistivity increased with annealing temperatures and the films were typical semiconductors. As catalyst, bismuth oxide films annealed at 550 °C had the best photocatalytic performance for photodegradation of methyl orange.     

Structural characterization,spectroscopic, thermal,AC conductivity and dielectric properties and antimicrobial studies of (C8H12N)2[SnCl6]

A new inorganic-organic hybrid material produced from 2,6-dimethylanilinium cations and tin halide (SnCl₆)^2? has been synthesized and structurally determined by X-ray diffraction method. The title compound crystallizes in the monoclinic system, space group C2/m with a = 19.8772(4), b = 6.9879(1), c = 8.3001(2) Å, β = 98.487(2)° and V = 1140.26(4) ų. The crystal structure is built up of sheets of (SnCl₆)^2? octahedral anions and 2,6-xylidinium cations. The optical band gap was calculated and found to be 4.11 eV. At high temperature this compound exhibits a structural phase transition at 338 K. This has been characterized by differential scanning calorimetric and dielectric studies. Measurements of AC conductivity as a function of frequency at different temperatures indicated the hopping conduction mechanism. The bioassay results showed that the structure exhibits significant antibacterial activity.     

Effect of thermal history and characterization of plasticized,composite polymer electrolyte based on PEO and tetrapropylammonium iodide salt (Pr4N+I-)

The search for anionic conductors based on solid polymer electrolytes is important for the development of photo-electrochemical (PEC) solar cells due to their many favourable chemical and physical properties. Although solid polymer electrolytes have been extensively studied as cation, mainly lithium ion, conductors for applications in secondary batteries, their use as anionic conductors have not been studied in greater detail. In a previous paper we reported the application of a PEO based iodide ion conducting electrolyte in a PEC solar cell. This electrolyte had the composition PEO: Pr₄N⁺I^? = 9:1 with 50 wt.% ethylene carbonate (EC). In this work we have studied the effect of incorporating alumina filler on the properties of this electrolyte. The investigation was extended to electrical and dielectric measurements including high frequency impedance spectroscopy and thermal analysis.In the DSC themograms two endothermic peaks have been observed on heating, one of these peaks is attributed with the melting of the PEO crystallites, while the other peak with a melting temperature ~ 30 °C is attributed to the melting of the EC rich phase. The melting temperature of both these peaks shows a marked variation with alumina content in the electrolyte. The temperature dependence of the conductivity shows that there is an abrupt conductivity increase in the first heating run evidently due to the melting of the EC rich phase. High conductivity values are retained at lower temperatures in the second heating. Conductivity isotherms show the existence of two maxima, one at ~ 5% Al₂O₃ content and the other at ~ 15%. The occurrence of these two maxima has been explained in terms of the interactions caused by alumina grains, the crystallinity and melting of the PEO rich phase. As seen from latent heat of melting, the crystallinity of the electrolyte has reduced considerably during the first heating run. In contrast to the conductivity enhancement caused by ceramic fillers in PEO-based cation containing electrolytes, no conductivity enhancement has been observed in the present PEO based anionic conducting materials by adding alumina except at low temperatures.