Using resistor-capacitor networks, sources of experimental artifacts in impedance spectroscopy were investigated, such sources include machine limitations, rig/cabling contributions at high frequencies, and artifacts due to high impedance reference electrodes and their geometrical placement. In the instance of electrode placement, computer simulations with a pixel-based model were in agreement with the experimental observations. Remedies for these artifacts such as rig shielding/grounding, geometrical adjustments, and null corrections are also discussed.

The factors determining electrical characteristics using immittance data of heterogeneous systems are not identical to those established with devices based on single-crystal/single-junction (SCSJ) technology. The ”state of normalization” using ”physical geometrical factors” of the asmeasured immittance quantities does not provide a SCSJ-like straightforward interpretation of simultaneously operative phenomena. The normalization procedure can the vitiate identity of each phenomenon occurring within the series-parallel microstructural network of electrical paths. The advantage of using the as-measured immittance data in delineating simultaneously operative phenomena is emphasized. An approach to data-handling/analyzing is proposed considering the limitations and conditions of utilizing the as-measured immittance data. The ”state of normalization” using ”physical geometrical factors” can only be executed for a specific type of phenomenon when isolated from the total electrical behavior.

Two techniques for measurement of local electrical conductivity of inhomogeneous materials are described. I) A novel variant of the impedance technique for thin/thick film characterization was developed; due to the two-dimensionality of the cell set up, at different frequencies different parts of the material are probed. The technique was experimentally verified by measuring the position coordinate of a Ag strip artificially added to a AgCl film. Its application to the Ag/AgCl boundary is touched upon. II) Micro-electrodes were used to probe surface conductances and local subsurface conductivities. The technique was implemented by a home-made high impedance adapter and combined with AFM to measure the contact area. Several examples of application are shown, viz. measurements of a) the enhanced surface conductivity of mechanically polished AgCl crystals, b) the interdiffusion coefficient of Cd2+ in AgCl, and c) the grain conductivity of polycrystalline AgCl.

Coating failure initiates as a local event at defects which can result from chemical heterogeneities in the resin or physical defects such as bubbles, underfilm deposits, or pinholes. The ability to detect, map the location, as well as make quantitative in-situ measurements of coating heterogeneities will help identify the source of failure (i.e. coating chemistry, method of application, cure schedule, etc.) and provide insight into the mechanisms of coating degradation. This study used a 5 electrode arrangement to perform local electrochemical impedance spectroscopy (LEIS) on coated steel substrates. Using single frequency measurements, LEIS could successfully detect and map both intentional chemical heterogeneities and physical defects such as subsurface bubbles, underfilm deposits, and pinholes. Efforts to optimize probe design and instrumentation are ongoing.

Impedance spectroscopy has been widely used to analyze polarization phenomena in dielectric, ferroelectric and solid electrolyte materials. In this paper, we review its extension to ferromagnetic materials, and discuss its application to the case of irreversible domain wall displacements which lead to ferromagnetic hysteresis phenomena.

A six-electrode impedance chamber is used to perform wide-bandwidth (10 Hz − 3 MHz), sensitive impedance measurements to evaluate the electrical properties of living cells under normal physiologic conditions. The high sensitivity in these measurements, compared to cell suspension techniques, is accomplished by embedding the cells into the pores of a filter, creating a “pseudoepithelium” and markedly reducing the current shunt pathways around the cells. The shunt resistance for each cell is between 6 − 7 × 107 Ω. The cellular geometry and the portion of cell membrane under measurement are precisely controlled in this method. This technique produces a multi-parallel, whole-cell, patch-clamp like structure for 3.3 × 105 cells. The advantages of this technique, general insights, and improvements in impedance measurements will be discussed. Effects of bandwidth mismatch between high-input impedance amplifiers, reference point drift due to solution resistivity changes, and the use of porous electrodes will be covered. Lastly, the ability to electroporate the cell membrane contributes another unique way to study the impedance of living cells.

The improvement of process yields and efficiency are often dependent upon the availability of sensors that allow real-time in-process control. The sensitivity of impedance techniques to physical, chemical, and microstructural features of a material system offers significant potential in developing real-time sensors. Two examples of how impedance techniques can be used to follow changes in materials throughout out a process are discussed. The first of these involves monitoring the processibility and viability of solder pastes used in surface mount technology. The second example deals with monitoring the state of an ion exchange resin bed as used in water softeners.

Immittance spectroscopy [IS] involves the measurement of the small-signal frequency response of dielectrics, semiconductors, electrolytes, biological cells, and polycrystalline, amorphous, and single-crystal electrically conducting materials. Analysis of such data to provide insight into the detailed, microscopic, physicochemical processes present in the full electrode and bulk material system is a crucial part of IS. Background information on IS and a discussion of its strengths and weaknesses are presented. The use of weighted, complex, nonlinear-least-squares for direct data fitting and for the solution of the ill-posed inversion problem of estimating continuous distributions of activation energies for important response models and for experimental data is illustrated. Replacements for the widely used, but incorrect, complexelectric- modulus data-analysis relations proposed long ago by C. T. Moynihan and associates for disordered ionic conductors, are presented and discussed. Recent proposals for various kinds of universal response behavior are examined and found to be unjustified. The present analysis methods are illustrated by applying them to 24°C data on a lithium aluminosilicate glass and to data over a wide temperature range on single-crystal CaTiO3:30%Al3+

The dynamics of densely packed interacting systems including glass-forming materials and glassy ionic conductors of various chemical and micro structures have been investigated experimentally by many workers, covering an immense time range from microscopic times shorter than 10−12 s to macroscopic times as long as 104 s. The short time dynamics is fundamental because it can directly reveal the microscopic mechanism of the relaxation. Several experimental investigations of structural relaxation in glass-forming substances have found that the short time dynamics shows exponential relaxation with a correlation function well described by exp(−t/τo) for t<tc where tc is temperature insensitive and has the order of magnitude of a picosecond. The correlation function then crosses over at tc to assumes the stretched exponential form, exp[−(t/τ)β], for t>tc. The relaxation times τ and τo are related by the expression τ = [tc−(1−β)τo]1/β. In this work, we focus on glassy ionic conductors and ionic glass-forming materials and experiments that employ dielectric spectroscopic and conductivity relaxation techniques, the theme of this Symposium. We show that these experimental data exhibit the same feature as described above for structural relaxation and are in accord with the predictions of the coupling model proposed by one of the authors.

The behavior of the frequency dependence of the conductivity, σ(ω), of numerous crystalline materials and glasses is close to an ω1.0 dependence in the limit of low temperatures and/or high frequencies (referred to as the “nearly constant loss”, or NCL, regime). Detailed analysis of this behavior, including the frequency dependence of both ε′ and ε″, shows that it can be described phenomenologically as produced by a broad distribution of asymmetric double-well potentials (ADWPs) with low activation energies. In order to obtain an understanding of the atomic origins of such potentials, we investigate the composition dependence of this behavior in such materials as crystalline CeO2:1%Y3+ ceramics with variable [Y3+] and alkali germanate glasses with variable alkali concentration. The appearance of a discrete loss peak in CeO2: 1%Y3+ helps us understand the ADWPs as due to “off-symmetry” configurations that undergo wiggling motion between adjacent minimum-energy positions.

The concurrent multiple complex plane representation of the single/multiple semicircular relaxation(s) for the same immittance data provides a choice of selecting simultaneously operative phenomena within a heterogeneous system. The origin of this representation and the selection criteria of the phenomena are highlighted via structure-property-processing relationships. These include the development of a single equivalent circuit model by acquiring knowledge on the type of aterials, history, chemistry, composition, processing variables, microstructures, etc. The correspondence within the complex planes is attributed to the relative magnitudes of the contributing elements in the equivalent circuit model and dominance of the operative phenomena. The limitations concerning the transformation of the data from one complex plane to the other are reviewed, considering Debye/non-Debye conduction processes within the series-parallel microstructural network of electrical paths.

In conductivity spectroscopy, ionic conductivities of solid electrolytes are measured continuously from a few Hertz up to the mid-infrared, i.e., in a frequency range covering more than twelve decades. In this paper we present experimental conductivity spectra of various cryst alline and glassy ionic conductors. Tracing the characteristic patterns of the spectra back to their generic processes provides a powerful means for probing the motion of the ions on atomic scales of space and time. The technique is particularly useful for exploring the single-particle potentials felt by the ions and, hence, for elucidating details of the surrounding structure. In our examples we discuss widths, anisotropies, and geometrical arrangements of sites in crystals as well as the existence of non-equivalent sites in glass.

The dependence of dc electrical conductivity of a series of rubidium germanate glasses on rubidium oxide concentration is correlated with the structural information obtained from extended x-ray absorption fine structure analysis, density, x-ray photoelectron, Raman and far infrared absorption spectroscopy. Previously macroscopic molar or excess volume showed the most obvious correlation with the activation energy of conductivity. The present results demonstrate additional importance of the intermediate range structure.

The structure of PbSnF4 is derived from that of fluorite-type β-PbF2 The replacement of half the lead by tin results in a thousand-fold increase of the fluoride ion mobility, even though tin-fluorine bonds are strongly covalent. This is due to an increase of fluoride ion disorder on some sites. The structure of α-PbSnF4 can be interpreted as resulting from the insertion of two layers of [SnF]+ cations between each pair of layers of PbF8 cubes. This has profound bearings on the texture and properties of this material, since the tin(II) stereoactive lone pairs create very effective cleavage planes. In addition, the fluorine covalently bonded to tin occupy all vacant sites used to create Frenkel defects. However, superionicity is observed by complex impedance measurements. Transport number measurements show that fluoride ions are the charge carriers.

Complete ionic conductivity spectra have been taken of solid silver chloride and silver bromide at various temperatures. The spectra contain two new dynamic features: i) a thermally activated Debye-type relaxation which is explained by the frequent hopping of silver ions from their regular lattice sites to adjacent interstial sites and back again, and ii) conductivity maxima at about 500 GHz which are attributed to high-amplitude individual vibrational motions, mostly of the silver ions. – We also report results of a neutron scattering study on silver bromide. These contain thermally activated quasielastic contributions caused by the localized cation back-and-forth hopping and also give evidence of fast correlated movements of neighboring ions.

The ceramic Sr-Fe-Co-O has potential use as a membrane in gas separation. This material exhibits high conductivity of both electrons and oxygen ions. It allows oxygen to penetrate at high flux rates without other gas components. Electrical properties are essential to understanding the oxygen transport mechanism and defect structure of this material. By using a gas-tight electrochemical cell with flowing air as the reference environment, we were able to achieve an oxygen partial pressure (P02) as low as 10−16 atm. Total and ionic conductivities of Sr-Fe-Co-O have been studied as a function of P02 at elevated temperature. In air, both total and ionic conductivities increase with temperature, while the ionic transference number is almost independent of temperature, with a value of ≈0.4. Experimental results show that ionic conductivity decreases with decreasing P02 at high P02 (≥10−6 atm). This suggests that interstitial oxygen ions and electron holes are the dominant charge carriers. At 800°C in air, total conductivity and ionic conductivity are 17 and 7 S/cm, respectively. Defect dynamics in this system can be understood by means of the trivalence-to-divalence transition of Fe ions when P02 is reduced. By using the conductivity results, we estimated oxygen penneation through a ceramic membrane made of this material. The calculated oxygen permeability agrees with the experimental value obtained directly from an operating methane conversion reactor.

Compounds of IVb and Vb transition metals and carbon are electronically conductive, hard materials that crystallize in the NaC1 structure but are very nonstoichiometric (carbon-poor), as in TiCx, where x is the carbon/metal ratio and is less than unity. Carbon atom vacancies are randomly located in the fcc carbon sublattice and act as scattering centers for conduction electrons. Data on the electrical resistivity as a function of the concentration of these point defects could be used in the opposite sense–i.e., to determine the defect concentration, (l-x), through a measurement of resistivity. The chemical composition (carbon/metal ratio) is then given directly by x. The random vacancies can be ordered by slow cooling from high temperatures, thereby eliminating the residual resistivity. The carbon/metal ratios of these ordered phases are either 3:4, 5:6 or 7:8 and thus can specify the chemical composition precisely.

Deep levels in II-VI compounds were investigated by complementary junction and optical spectroscopy methods to assess the characteristics of the traps as well as the limits and the reliability of the techniques applied. The electrical properties have been investigated by current and capacitance transient spectroscopy, while the optical properties have been studied by cathodoluminescence. A critical and comparative analysis of the results obtained with the various methods allowed the determination of the parameters and the nature (majority or minority carrier trap) of most of the detected levels.

Spectroscopic ellipsometry (SE) is a powerful optical tool for non-destructively depth-profiling the dielectric function of samples with a resolution in the Ångstrom range. In this work, the characterization of graded composition layers in transparent materials by SE is described. In modeling studies on the sensitivity limits of the technique, it has been shown that for known index profile shapes, the depth sensitivity can be quite high. For example, diffusion of Na2O into the surface of a vitreous silica sample can be detected for layers as thin as 100Å when the maximum refractive index contrast is only 0.005. The sensitivity of the technique increases as the diffusion depth and refractive index contrast increases. The accuracy of the thickness determination depends on the total thickness of the graded layer; for a given system, the accuracy of the composition measurements do not depend on the surface concentration.

Leached alkali-aluminosilicate and modified lead silicate glasses were examined by SE to experimentally confirm the modeling predictions on the composition depth profiling. Extremely good correlation between the SE-determined depth profile and SIMS measurements on similar samples was obtained for the case of the modified lead silicate glass. For the aluminosilicate glass, simultaneous roughening of the glass surface during etching makes composition profiling more difficult.

We used the Kramers-Kronig transformation to investigate the local dielectric function of barium titanate, BaTiO3 from regions of sub-micrometer scale. Further the effect of dopants, in this case, Nb, on the dielectric function was investigated to assess the level of its local partitioning in the BaTiO3 lattice. The transmission electron energy loss spectroscopy technique was used to obtain dielectric function by placing a small electron probe in isolated regions of the electron transparent BaTiO3 samples. We observed an anomalous, but consistent, shift in the volume plasmon in all regions of the doped sample (compared to the pure one) indicating a uniform incorporation of the dopant within the lattice.