Ionic conduction through heterogeneous solids: Delineation of the blocking and space charge effects

The conductivities of an ionic polycrystalline solid lithium iodide (LiI) and covalent, polycrystalline lithium aluminum titanium phosphate (LATP) glass-ceramic material with Al₂O₃ and Ba_0.6Sr_0.4TiO₃ (0.6BST) additions were investigated. It was determined that blocking and space charge effects coexist in these heterogeneous solids. However, their magnitudes differ from one system to another. The most pronounced blocking effect was evident in the LATP–Al₂O₃ system, whereas a dominant space charge effect was observed in the LiI–Al₂O₃ system. The higher dielectric constant of 0.6BST enhanced space charge effect in the LATP–0.6BST system. The space charge effect was also found to be temperature dependent.     

Monitoring the Channel Formation in Organic Field‐Effect Transistors via Photoinduced Charge Transfer

Conducting channel formation in organic field‐effect transistors (OFETs) is considered to happen in the organic semiconductor layer very close to the interface with the gate dielectric. In the gradual channel approximation, the local density of accumulated charge carriers varies as a result of applied gate bias, with the majority of the charge carriers being localized in the first few semiconductor monolayers close to the dielectric interface. In this report, a new concept is employed which enables the accumulation of charge carriers in the channel by photoinduced charge transfer. An OFET employing C₆₀ as a semiconductor and divinyltetramethyldisiloxane‐bis(benzocyclobutene) as the gate dielectric is modified by a very thin noncontinuous layer of zinc‐phthalocyanine (ZnPc) at the semiconductor/dielectric interface. With this device geometry, it is possible to excite the phthalocyanine selectively and photogenerate charges directly at the semiconductor/dielectric interface via photoinduced electron transfer from ZnPc onto C₆₀. Thus the formation of a gate induced and a photoinduced channel in the same device can be correlated.     

Space Charge Signature and Its Effects on Ionic Transport in Heterogeneous Solids

The Arrhenius plots of heterogeneous solids comprising of lithium aluminum titanium phosphate (LATP) glass–ceramic, Al₂O₃, and Ba_0.6Sr_0.4TiO₃ (0.6 BST) exhibit an inflection or peak around 27°C, which is interpreted as a signature of space charge. The space charge is formed by the adsorption of lithium ions onto the dielectric phases below 27°C. The space charge is also a source of an electric field, which influences the transport of conducting ions. The adsorbed ions are desorbed above 27°C, resulting in a reduction or elimination of the space charge effect. A high dielectric constant phase, 0.6 BST, retains the space charge effect even at temperatures greater than 27°C.     

Applied whispering gallery modes on ZnO nanorods coated glass for humidity sensing application

In this letter, a humidity sensor is demonstrated by applying a whispering gallery mode (WGM) from a microsphere resonator onto the ZnO nanorods coated glass surface. The diameter of the microsphere was 234 µm and the glass surface was coated with ZnO nanorods using the hydrothermal method at growth duration of 12 h. A significant response to humidity level ranging from 35%RH to 85%RH has been observed with the sensitivity of 0.014 2 nm/%RH. The proposed humidity sensor has successfully employed to enhance interaction between the whispering gallery mode evanescent and surrounds analyte with the assistance of ZnO nanorods coated glass.     

Internal fluid motion and particle transport in externally heated sessile droplets

Experiments and numerical simulations were carried out for an evaporating sessile droplet. The droplet was confined in the narrow gap between two glass plates, making it a “Hele‐Shaw” droplet and particle image velocimetry technique was used. In case of the evaporating droplet with pinned contact line and exposed to ambient condition, two symmetric but counterrotating convection cells were observed. After complete evaporation, the particles deposited on the substrate near the contact line. The direction of the flow was reversed for a droplet placed on uniformly heated substrate, and the final deposition pattern was a large spot at the center with a thin line at the periphery. For asymmetrically heated substrate a single convection cell appeared, and the final deposition was also asymmetric. When the liquid was subjected to localized heating, the contact line no longer remains pinned and a relatively uniform deposition was obtained after complete drying. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1308–1321, 2016     

Composite effect in superionically conducting lithium aluminium germanium phosphate based glass-ceramic

Superionically conducting lithium aluminum germanium phosphate (LAGP) glass-ceramic and barium strontium titanate, Ba_0.6Sr_0.4TiO₃ (0.6BST)-doped specimens were processed and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and AC impedance techniques. The XRD patterns exhibited the existence of LiGe₂(PO₄)₃ as the primary phase with impurity phases AlPO₄ and Li₂O. SEM images revealed the presence of large LAGP crystals. The highest conductivity (5.08 × 10⁻³ S cm⁻¹) at 27 °C was obtained for the glass-ceramic sheet specimen crystallized at 850 °C for 12 h. Pelletized specimens prepared from the glass-ceramic powder and sintered at 850 °C for 9 h exhibited a slightly lower conductivity (4.62 × 10⁻³ S cm⁻¹) at 27 °C. The nonlinearity in the Arrhenius plots of total conductivity was attributed to the impurity phases, AlPO₄ and Li₂O and mediated the transport of lithium ion which is associated with higher activation energy. Doping of dielectric 0.6BST to the LAGP led to the shifting of the temperature of inflection towards the higher temperature in the Arrhenius plot of total conductivity and enhanced the space charge effect.     

Heterogeneous electrolyte (YSZ–Al2O3) based direct oxidation solid oxide fuel cell

Bilayers comprised of dense and porous YSZ–Al₂O₃ (20 wt%) composite were tape cast, processed, and then fabricated into working solid oxide fuel cells (SOFCs). The porous part of the bilayer was converted into anode for direct oxidation of fuels by infiltrating CeO₂ and Cu. The cathode side of the bilayer was coated with an interlayer [YSZ–Al₂O₃ (20 wt%)]: LSM (1:1) and LSM as cathode. Several button cells were evaluated under hydrogen/air and propane/air atmospheres in intermediate temperature range and their performance data were analyzed. For the first time the feasibility of using YSZ–Al₂O₃ material for fabricating working SOFCs with high open circuit voltage (OCV) and power density is demonstrated. AC impedance spectroscopy and scanning electron microscopy (SEM) techniques were used to characterize the membrane and cell.     

Space Charge-Mediated Ionic Transport in Yttria-Stabilized Zirconia–Alumina Composite Membranes

This paper reports ionic conductivity of yttria-stabilized zirconia (YSZ)–Al₂O₃ composite membranes. The tape cast specimens were subjected to binder burnout (500°C) and sintering (1550°C) processes to obtain 200–300 μm thick membranes. The ionic conductivity and microstructure of the membranes were characterized and are discussed in this paper. The ionic conductivity of the composite specimens was enhanced and was correlated with the number of charge carrier and their mobility. The solubility of Al₂O₃ in YSZ was minimal and nanosize Al₂O₃ of the batch sintered into microsize and existed as a distinct phase. The scanning electron microscopy micrographs revealed that YSZ and Al₂O₃ grains were strained.     

Ionically Conducting Composite Membranes from the Li2O–Al2O3–TiO2–P2O5 Glass–Ceramic

This paper reports processing of lithium ion-conducting, composite membranes comprised of 14Li₂O·9Al₂O₃·38 TiO₂·39P₂O₅ glass–ceramic and polyethylene. The processing involved tape casting of 14Li₂O·9Al₂O₃·38TiO₂·39P₂O₅ glass powder with organic additives into tapes, subjecting the green tape to binder burnout and thermal soaking in the temperature range of 950°–1100°C, and finally infiltrating the porous tape with polyethylene solution. The ionic conductivity and microstructure of 150–350 μm thick membranes were characterized and are discussed in this paper. The crystallites of the glass–ceramic show liquid-like conductivity at ambient temperature, whereas the grain boundary conductivity is lower by a factor of five. The lower grain boundary conductivity is explained on the basis of crystallographic mismatch and the existence of AlPO₄ at the grain boundary. The polyethylene infiltration in the porous membrane improved mechanical resilience with a minor adverse effect on conductivity.