A. Lusis

Electrochromic colour centres in amorphous tungsten trioxide thin films

Abstract Amorphous tungsten trioxide films, investigated by the Raman scattering method, are shown to be composed of a spatial network of tightly bound (WO6)n·mH2O clusters with a large number of terminal oxygen W=O and W-O-W bonds between clusters. The injected electrons in an amorphous tungsten trioxide film are localized in the tungsten 5d orbitals in an axially distorted octahedron, as is shown by ESR analysis. The optical absorption of a coloured amorphous tungsten trioxide film, as has previously been proposed, can be satisfactorily described by an intervalence charge-transfer transition between localized W5+ and W6+ states.

Proton conducting composite electrolytes based on antimonic acid

Abstract This report concerns a composite proton electrolyte suitable for use in electrochromic devices. The electrolyte consists of nanosize pyrochlore antimonic acid particles suspended in a poly(vinyl acetate) matrix by a gel route. It was found possible to substitute the antimonic acid by inert oxides of aluminum and silicon, thus making the electrolyte less harmful to the oxide electrodes of the electrochromic devices without considerably decreasing the conductivity. The proton conductivity of the antimonic acid electrolyte was ∼10 −4 S/cm at room temperature, practically independent of its amount of absorbed water.

Antimonic acid hydrate xerogels as proton electrolytes

Abstract Two high stability types of protonic solid electrolytes based on antimonic acid hydrate xerogels have been obtained by the sol-gel technique: Sb 2 O 5 ·(3–4)H 2 O (colloidal) and Sb 2 O 5 ·5H 2 O (polymeric). The first one is a white compact material with conductivity 0.40 mS/cm (298 K) for n =3.7. The last one is transparent for visible light with a conductivity of 0.80 mS/cm. An electrochromic system based on the colloidal gel electrolyte in the form of paste has good performance-more than 10 7 cycles and a lifetime of more than five years.

Electrochromism in tungsten oxyfluoride films made by chemically enhanced dc sputtering

Tungsten oxyfluoride films were prepared by reactive dc sputtering in plasmas containing O2+CF4.. The deposition rate was large, particularly when chemical sputtering was promoted by heating the target. The films could show large charge insertion/extraction and high coloration efficiency.

Sol-gel produced humidity sensor

Abstract The sol-gel produced polycrystalline Prussian Blue thick films as planar humidity sensors have been investigated by impedance spectroscopy. The equivalent circuit used allows simulation in all the investigated r.h. range (10–100%). The region of changes of sample resistance is about five orders, which is enough for high measuring sensitivity.

Gas-sensitive gap formation by laser ablation in In2O3 layer: application as humidity sensor

Abstract A new method of preparing a gas-sensitive device by laser ablation of a thin gap in a thin conducting In2O3 layer has been discovered. In the bottom of the gap no products from In2O3 are found, thereby indicating that the reorganized surface of the glass substrate is responsible for the humidity sensitivity. Impedance spectra of the gap processed by a laser beam are measured in the humidity range RH25–100% at temperatures T0–45°C, where a linear dependence of the logarithm of resistivity on the values of humidity is estimated.

Electric and dielectric properties of nanostructured stoichiometric and excess-iron Ni?Zn ferrites

In this paper, we report a study of the effect of excess iron on structural, microstructural, electric and dielectric properties of the nanostructured Ni–Zn ferrites Ni1−xZnxFe2+zO4−δ of different compositions with x = 0, 0.3, 0.5, 0.7, 1 and z = 0, 0.1. The structural and microstructural properties are estimated from x-ray diffraction and atomic force microscopy (AFM) data. The average grain size, evaluated from AFM topographical analysis, is found to be below 70 nm. The samples exhibit low values of dielectric constant and dielectric loss and a high resistivity. Contrary to earlier conclusions regarding microstructured Ni–Zn ferrites, in nanostructured Ni–Zn ferrites sintered at relatively low temperature and duration, the excess of iron in the composition increases the electrical resistivity and reduces the dielectric constant and loss tangent.

Nature of fundamental absorption edge of WO3

The fundamental absorption edge of amorphous, polycrystalline and crystalline tungsten trioxide (WO3) thin films obtained by different techniques (thermal evaporation, rf plasma sputtering, chemical gas transport) was investigated. Special attention was paid to correct measurements of absorption values of all WO3 thin films taking into account the scattered light, interference effects and reflection losses. The indirect edge at 2.70 eV was determined for crystalline WO3, but for crystal WO3:Ti the direct edge in the same place (2.72 eV) was found. For polycrystalline WO3 thin film first edge transition located at 2.76 eV had a quadratic dependence similar to the amorphous film at a higher photon energy (3.26 eV). Localized states are involved in these transitions with quadratic dependence. The gap energy shift from crystalline to amorphous WO3 is explained by changes in the first coordination sphere of octahedral WO3 cluster. Higher direct allowed transition at 4.1 eV is estimated both for amorphous and polycrystalline thin WO3 films.

Gaseous sensors based on solid proton conductors

Abstract he chemical sensors for different gaseous (alcohol, acetone, ammonia, water vapour) detection at room temperature are developed by using polycrystalline β-alumina and xerogel of antimonic acid hydrate (AAH). The sensitivity and selectivity of sensors depend on the ion-exchange and preparative methods. The possibility of producing different types of potentiometric, amperometric, voltammetric and resistance sensors on the basis of these ion-conducting materials is shown. More success is achieved by producing ammonia-sensitive devices on β-alumina as well as on AAH xerogel.

Characterization of LiFePO4/C Composite Thin Films Using Electrochemical Impedance Spectroscopy

The composite LiFePO4/C thin films were prepared on steel substrate by radio frequency (RF) magnetron sputtering. Electrochemical properties of the obtained thin films were investigated by cyclic voltammetry charge-discharge measurements and electrochemical impedance spectroscopy (EIS). The films annealed at 550 °C exhibited a couple of redox peaks at 3.45 V vs. Li/Li + characteristic for the electrochemical lithium insertion/extraction in LiFePO4. At low current rate such composite thin film showed a discharge capacity of over 110 mAh g -1 . The dependence of charge transfer resistance, double layer capacitance and lithium diffusion coefficients on applied electrode potential were calculated from EIS data. Determined values of lithium diffusion coefficient were in the range from 8.3·10 -13 cm 2 s -1 to 1.2·10 -13 cm 2 s -1 at 3.4 V and 3.7 V, respectively.