Selected findings of ongoing investigations of variable light-transmission electrochromic devices using electronically conducting polymers as electrochromic materials are presented and discussed.

An obvious requisite for electrochromic windows is an all-solid configuration with polymer electrolyte; in this connection testing data of a new hybrid electrolyte based on a polymer network including a plasticizer are reported and discussed.

Thin films of polypyrrole were synthesized using both chemical oxidative and electrochemical methods. The resulting oxidized films were characterized by UV/VIS spectroscopy, contact angle and conductivity measurements. In vitro studies suggest that extracellular matrix molecules, such as fibronectin, adsorb efficiently onto polypyrrole thin films and that 3T3 Balb/c mouse fibroblasts attach and spread normally on polypyrrole.

Poly(carbon disulfide) was studied by cyclic voltammetry using glassy carbon and platinum macro- and microdisk electrodes. The electron transfer kinetic is significantly faster at glassy carbon electrodes than at Pt electrodes. It is chemically reversible with moderate electron transfer rates. Voltammetric results of poly(carbon disulfide) are in good agreement with our battery testing data. The k0 value measured at a Pt microdisk electrode is 7×10−3 cm/sec. Electrochemical data suggest that PCS can be a potential cathode material for low current density lithium batteries.

Ion diffusion across material interfaces is considered in a sequence of approximations with increasing complexity. First, the one-dimensional lattice gas model of particle diffusion is generalized to include a finite width interface region, and the possible existence of an energy barrier at the interface. Overvoltage measurements on InSe, and dielectric loss measurements on B2O3 - 0.5Li20 - 0.15Li2SO4 are used to determine the field-free hopping rates in the two materials. It is shown that the energy barrier is a dominant parameter. This model is then modified by considering the disorder of the glass structure and the blocking effect resulting from the ion interaction. Next, a more rigorous treatment is presented by solving the Poisson equation with appropriate boundatry conditions, and a self-consistent theory of the ionic diffusion is proposed. To clarify this problem, an intermediate step and two additional models with increasing sophistication are considered: first, the potential φ(x) of the moving charge density n(x) is calculated and it is shown that φ(x) is not negligible. Then, a feed-back is provided by including this potential in the diffusion equation. This treatment is already self-consistent and more realistic but leads to long computations even for the simple one dimensional lattice-gas model. A remedy of this difficulty is proposed whereby the theory is reformulated in order to guarantee from the beginning the self-consistency of the solution of the non-linear diffusion problem. Straightforward extensions to the two-dimensional case are then possible. The results of the computations are illustrated with numerical examples for different values of the physical parameters.

Although there has been much success in theoretical modelling of fast ion conductors with molecular dynamics simulations, there has been less attention paid to development of a chemical understanding of fast ion conduction. In this paper we explore the importance of core level interactions and the role that they play in constructing high diffusivity paths in solids. In particular, we have carried out molecular orbital calculations (using the self-consistent-field X-alpha scattered-wave method) on AgI clusters to examine the orbital interactions of the filled Ag 4d level. We hypothesize that it is the interaction of the d electrons that is responsible for fast ion conduction in AgI and other Ag and Cu binary fast ion conductors. The results of these calculations will be compared with other electronic structure calculations and XPS data.

Based on the examination of the relaxation process of the motion of a single particle in the assembly of particles of the same species, it is shown that the relaxation process of the motion of a particle in a lattice gas model is intrinsically non-Debye. The origin of this effect is traced to the deviation of the motion of particles from equilibrium immediately after their jumps.

Many disordered materials both crystalline and glasses show universal dynamic response [1], which is characterized by appropriate power-laws. The ac-conductivity as a function of frequency, is given by: σ(ω)=σ(0)+ Aωs where σ(0) is the dc-conductivity and the exponent s (≤1) generally decreases with increasing temperature. In previous work on ionically conducting crystals and glasses, we have observed two ranges in which s = constant, independent of temperature: at high temperatures, s=so (a value between 0.5 and 0.6) and, at low temperatures, s = 1. Further for the s = so region, the parameter A is activated with activation energy related to that of σ(0), while for the s = 1 region, A varies only slowly with temperature. For the cases of borate and silicate glasses as well as for crystalline CaTiO3 doped with 30% A13+, careful analysis was carried out over the region in which the effective s falls from 1.0 to so. The results show that this region can be described by the relation: σ(ω)= σ(0) + Aωs0 + A'ωl.0 with parameters A and A’ consistent with those obtained from the high and low- temperature regions, respectively. Thus, we conclude that two separate types of universal behavior are superimposed throughout the entire temperature region; each is described by a constant value of s, and is due to an independent mechanism of non-Debye relaxational behavior.

Using the molecular dynamics (MD) method, the nature of crystalline fragments in SiSe2 glass (a-SiSe2) at normal pressure, structural transformation and the loss of intermediate range order in SiO2 glass at very large positive pressures, and the modification of SiO2 glass network at very large negative pressures have been investigated. Implementations of the MD algorithm on the Connection Machine and Intel iPSC/860 machine are discussed.

Molecular dynamics (MD) simulations of porous silica, in the density range 2.2 - 0.1 g/cm3, are carried out on a 41,472 particle system using two- and three-body interatomic potentials. Calculated results for fractal dimension and small-angle neutron scattering data are in good agreement with neutron scattering experiments. Results for structural correlations reveal crossovers from the short- to intermediate range (< 8 Å) and fractal to large-scale regime (10 ∼ 100 Å).

The MD program simulations are carried out on distributed-memory MIMD computers using a domain-decomposition algorithm. The algorithm employs the linked-celllist method and separable three-body force calculation. The force calculation is accelerated by the multiple-time-step method. The parallel algorithm is highly efficient (parallel efficiency = 0.974), as it involves only 3 % communication overhead.

On the basis of a previously described structural model for the Yttria-Stabilized Zirconia, the conductivity for this material can be calculated. A fixed number of clusters is generated in a structure of 70×28 polyhedra to simulate different Y contents in the structure. The results are compared with the experimental results obtained by others and discussed.

Pressure-induced structural transformation from tetrahedral to octahedral coordination and the destruction of intermediate-range order (IRO) are studied in silica glass (a-SiO 2) using the molecular-dynamics (MD) method. Changes in the position and height of the first sharp diffraction peak (FSDP) in the static structure factor, bond lengths, coordination numbers, bond-angle distributions, and statistics of rings are investigated as a function of density. Modifications of the vibrational density of states and participation ratio are also discussed.

Molecular-dynamics simulations are performed to investigate structures, vibrational spectra, and fragmentation channels of silicon microclusters ranging in size from 32 to 52 atoms. Structural information is derived from pair-distribution functions, bond-angle distributions, and the structure and statistics of rings. Molecular-dynamics simulation results for energetics suggest that 33, 39, 45 and 51 atom clusters are highly stable. These magic-number clusters have predominantly five and six membered rings. With an increase in “temperature”, most clusters tend to fragment by loosing one atom at a time. Vibrational densities of states of 32-52 atom silicon clusters show only minor deviations from the bulk behavior.

The sol-gel process offers new opportunities for the synthesis of ionic materials, specially in the shape of thin films. Hydrous oxides are obtained which exhibit specific properties arising from strong interactions betwwen adsorbed water molecules and the oxide network. Sol-gel derived coatings are good candidates as electrode materials for lithium batteries or electrochromic devices. Their open structure allows easier diffusion of Li+ ions in the liquid phase while electrons are delocalized through the oxide network. Moreover, water molecules favor the formation of ordered phases leading to the deposition of layers with preferred orientation. Electrochemical insertion can then be described as an intercalation process between solid particles.

H-PFG-NMR diffusion and proton conductivity data for NAFION® 117 is presented as a function of temperature and water content. From this, H2O diffusion on a molecular scale is concluded to be similar to the one in bulk water. But “geometrical” restrictions of diffusion lead to a decreasing pre-exponential factor, i.e. decreasing macroscopic diffusion coefficient with decreasing water content. It is shown that proton conductivity is correlated with water diffusion for low degrees of hydration (vehicle mechanism). With increasing hydration there is an increasing contribution from “structure diffusion” culminating in an amplification factor of A = 2.5 for fully hydrated protonic NAFION® 117 at room temperature. The bonding of water in NAFION® as well as the local environment (hydration) of the acidic proton are concluded to be similar as in acidic aqueous solutions.

The properties of various proton conducting solid electrolytes were investigated by electrochemical galvanic cell and ac impedance type measurements for applications as high temperature (T>200°C) humidity sensors. The basic characteristics of proton conductors required for humidity sensing are reviewed. Results of ionic conductivity and EMF measurements and their implications for the mechanism of ion transport are discussed for two prototype ceramic humidity sensors: β-Ca(PO3)2 and a NASICON-type ceramic composite, HZr2P3O12/ZrP2O7.

Compounds that consist of intergrowths between the Aurivillius phase Bi4Ti3O12 and brownmillerite-like slabs of BaMO2.5were synthesized and their oxygen ion conductivities investigated. Both BaBi4Ti3ScO14.5 and BaBi4Ti3InO14.5 display a discontinuity in their Arrhenius plots that appears to be caused by an oxygen vacancy order-disorder transition. Conductivity data for two Aurivillius phases BaBi4Ti4O15 and BaBi2Nb2O9 are included for comparison.

We have investigated ruthenium doped gadolinium titanate, Gd2(RuxTi1-x)2O7-δ with 0 ≤ x ≤ 0.2, to determine the role of variable valent Ru in influencing the defect structure and transport properties of the pyrochlore host. We have developed a defect chemical model to interpret electrical conductivity, thermoelectric power, and thermogravimetry data. We have found that Ru acts as an acceptor compensated in large part by oxygen vacancies, resulting in enhanced ionic conduction at low values of x. For larger values (x ≈ 0.05), electronic conductivity predominates which we attribute to electron migration by hopping through a Ru-derived defect band.

Brownmillerite-perovskite intergrowths of the type m(A2B2O5)*n(ABO3), where m = 1 and n = 1, were investigated with respect to cation ordering. It was found that Sr31n2ZrO8, Sr31n2HfO8, Ba3Sc2TiO8 and Ba31n2TiO8 form in a disordered cubic structure, while Sr3Sc2ZrO8 and Ba3Sc2ZrO8 form an ordered cation arrangement. The Arrhenius plots of the oxygen ion conductivity of Ba3Sc2ZrO8, Sr31n2HfO8, and Ba31n2TiO8 contain discontinuities that appear to be caused by an oxygen vacancy order-disorder transition. High temperature powder-X ray diffraction did not show any evidence for cation ordering that might otherwise have created the changes in activation energy in the conductivity plots.

The reaction of crystalline lithium-stabilized Na-β”-Alumina with zirconium(IV) chloride at 400°C for 303h has caused sodium ions to exchange with zirconium ions. An X-ray crystal diffraction study of both the parent lithium stabilized Na-β”-alumina (1) and the partially zirconium exchanged product (2) have been made at 147 K. Crystal data for 1: rhombohedral, R 3 m, a = 5.6037 (3), c = 33.6210 (86) Å, V = 914.31 (24) Å3. Crystal data for 2: rhombohedral, R 3 m, a = 5.5994 (5), c = 33.7711 (51) Å, V = 916.96 (16) Å3. Zirconiums in 2 reside, predominately, in the Beevers-Ross type site.

The electrical response of a self -supported film (CaUP) in contact with different electrolyte media was studied by impedance spectroscopy for electrolyte concentrations ranging between 10−4 M and 10−2 M.The film was placed separating two aqueous solutions of the generating electrolytes, at the same concentrations, and two systems: i) UO2(NO3)2/CaUP/H3PO4; ii)Ca(NO3)2/CaUP/H3PO4, were considered.

The film equivalent circuit and characteristic parameters (Rf and Wf) for both systems were determined. Result show an important dependence of Rf values with concentration, whlckis related to the electrolyte invasion into the film matrix, but no significant changes in Wf values were found. Due to the film nature, the ionic diffusion process associated to this circuit element is mainly attributed to the protons.