In this work specific film structures of Li–Nb–O/Li/Li–Nb–O are investigated by AC Impedance Spectroscopy measurements at different temperatures. This gives the opportunity to investigate properties of the material itself and, at the same time, to consider the influence of the grain boundaries on the ionic behavior of the polycrystalline Lithium Niobate. On the other hand, LiNbO3/Li/Cu multi-layers are studied as electrolyte/anode bi-layers and potential parts of “Li-free” microbatteries. The Li deficiency in the as deposited Li–Nb–O films is cured by forming a “sandwich” of Li–Nb–O/Li/Li–Nb–O, which after annealing becomes ionic conductor. The electrical behavior of an annealed film depends on two sources. The first is due to properties of the material itself and the second is based on the network of the grain boundaries. The average size of the grains is strongly influenced by the structure of the ohmic-contact/substrate. The electrical behavior of the electrolyte/anode interface of the “Li-free” structure LiNbO3/Li/Cu/Au is very similar to the impedance measurements of the single LiNbO3 single films. The whole multilayer structure, though, presents a third relaxation time which is consistent of a small resistance. This resistance is independent of temperature and it seems that is due to the metallic interface Li/Cu/Au.

The presence of crystalline phase in low and medium lithium content boron oxide glasses xLi2O–B2O3, with x=0.3–2.5, has been detected by combined infrared and impedance measurements. The borate glass samples apparently consist of one single phase, the vitreous. However, characteristic absorption bands appearing in infrared spectra of samples with x≥0.8 indicate the presence of crystalline Li2O. Further evidence is provided by the gradual appearance and disappearance with increasing temperature of an additional electrical relaxation in impedance spectra, corresponding to the crystalline phase present in the borate glasses, which is associated with Li2O.

Infrared and impedance measurements have been carried out on high lithium content boron oxide solid electrolytes xLi2O–B2O3, with x=3.0–4.5, in order to establish the correlation between their structural and electrical properties. The samples are two-phase materials, in which crystalline islands are scattered throughout the vitreous background phase. The evolution of structural and electrical properties with increasing x exhibits a marked differentiation around x=4.0, which is associated with increasing crystallization in the material.

e-Gun deposited bi-layer structures of LiCoO2/(Li2O)x·(B2O3) cathode material and solid electrolyte have been investigated by SEM and impedance spectroscopy. The crystallinity of the substrates, on which the structures are deposited, influences the extent of crystallization, and consequently the ionic conductivity, of the electrolyte layer. Comparison of impedance spectra between bi-layers and electrolyte single layers indicates that the total ionic conductivity of the electrolyte in the bi-layer is decreased with respect to the single layer, due to higher crystallization.

LiNbO3 thin films, deposited by e-gun evaporation, show lithium deficiency, which is cured by “Li doping”. The “Li doping” of the films was achieved by preparing a structure of Li-Nb-O/Li/Li-Nb-O, which after annealing forms a homogenized LiNbO3 layer because of diffusion of Li in the two Li-Nb-O layers. The LiCoO2/LiNbO3 bi-layers were prepared either on Stainless Steel/TiN or on Al2O3/Co/Pt substrates/ohmic-contacts by depositing first either the cathode LiCoO2 or the electrolyte LiNbO3. The Nyquist plots of the AC impedance measurements of all structures showed that the interfaces prepared on Stainless-Steel/TiN consisted of two semicircles. The structures deposited on Al2O3/Co/Pt showed a third semicircle, which is probably due to the roughness of the substrate. It is important that the ionic properties of the bi-layers with the cathode material deposited first, a usual structure in a microbattery, are improved compared to the other structures. The quality of the LiNbO3 layer depends very much on the substrate. It can be evaluated from Arrhenius plots that the activation energy of this layer is considerably lower when the whole structure is deposited on Stainless Steel/TiN. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An equivalent circuit model is introduced to account for the impedance properties of solid state ionic conductors, composed of two distinct phases. The model is developed on the basis of physical arguments, regarding the micrometer-scale structure of the two-phase material system and the comparison of different possible equivalent circuit representations. The final equivalent circuit reduces to two simpler circuits, suitable for fitting experimental impedance spectra. Computer simulations are provided to demonstrate the non-Arrhenius behaviour, which is observed in the temperature dependence of the ohmic elements of the equivalent circuits used for data analysis. This complex dual-slope behaviour of the Arrhenius plot is in agreement with the predictions of the model. Finally, with the aid of mathematical calculations and illustrated by computer simulations, a modified Arrhenius plot evaluation procedure was developed to derive correctly the electrical properties of the individual constituent phases from impedance measurements.

The equivalent circuit model of two-phase ionic conductors, introduced in Part I of this work, was applied to a set of x Li 2 O–B 2 O 3 fast-ion conducting glasses, with x ranging from 3.0 to 4.5. The shape of Arrhenius plots, constructed by equivalent circuit fitting of impedance spectra measured at various temperatures, turned out to be in agreement with the predictions of the model. The analysis procedure, which was developed by mathematical investigation in accordance with the implications of the model, was employed to determine the activation energies of the two present phases and the total DC ionic resistivity of the examined glasses.

Lithium mobate LiNbO3 was prepared as a thin film layered structure deposited on stainless steel substrate using e-gun evaporation. The Li doping was provided for by the formation of Li-Nb-O/Li/LiNb-O sandwich structure and annealing at about 250 degrees C. AC impedance spectroscopy measurements were performed on the samples at temperatures from the interval between 28 and 165 degrees C and in a frequency range of 10(-3) to 10(6) Hz. Using the values Z' and Z'' at different frequencies, the dielectric parameters - parts of the complex permittivity epsilon' and epsilon'' and loss tangent tan 8 were calculated. The results prove validity of the proposed equivalent circuit containing parallel RC elements connected in series where the first RC element represents the bulk of material and the second RC element belongs to the double layer at the metal interface. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lithium niobate, LiNbO3, thin films are mostly known for their technological applications in electrochromic displays or in all solid state thin film microbatteries. Various methods have been used for preparation of LiNbO3 thin films. Lithium niobate was prepared as a thin film layered structure using e-gun evaporation for this study. Metallic films of Li between two Li-Nb-O layers provided "Li doping" after some thermal treatment. The real and imaginary parts of the complex impedance, Z' Z", were measured and the loss tangent was calculated from the measured values of Z' and Z". Two different polarization processes were estimated from the acquired frequency dependencies of the loss tangent. An equivalent circuit, describing the behaviour of the samples, was proposed and the transport processes in the prepared samples are discussed.

The introduction of Co, Al, and Ti into LiMn2O4 cathode powders has been studied in this work. The substitution of 25% Mn with either of these metals is expected to improve the cycle ability of the cathode, while the Jahn–Teller effect is suppressed. The solid-state reaction method is used in order to produce the cathode materials, which are prepared at 750 or 800 °C. The materials are characterized by X-ray data and, electrochemically, by galvanostatic cycling at the 4-V range. Their capacity fading behavior is evaluated, and a further investigation into cycling at a higher voltage range is also presented.

Thin film bilayers of LiNbO 3 /C have been formed on substrates of stainless steel/TiN and Al 2 O 3 /Co/Pt. These samples have been treated thermally and measured with an AC impedance analyzer in order to evaluate their ionic behavior. Subsequently, solid state microbatteries, using LiCoO 2 as cathode material, have been prepared on the same substrates. Both the LiCoO 2 /LiNbO 3 /C and the inverse structure have been fabricated. AC impedance spectroscopy reveals that deposition of the electrolyte on the cathode layer is more active, while the substrate of the whole structure influences significantly the ionic resistivity of the electrolyte.

An interlayer of metallic Li was formed between two layers of Li–Nb–O. Annealing of the structure results to diffusion of Li into the two layers of Li–Nb–O, improving the ionic conductivity. The thickness of the metallic interlayer is a crucial parameter, as well as the temperature and time of annealing. The substrate strongly influences the electrical and structural properties of the films. Stainless-steel/TiN substrate seems to improve considerably the ionic conductivity of the films, the relaxation time of which is similar to that of the Lipon electrolyte.

Lithiated boron oxide glasses of the family xLi2O-B2O3, with x ranging from 1.0 to 4.5, were prepared by melting at high temperatures and shaped in the form of slabs. The glasses’ properties were evaluated by Complex Impedance Spectroscopy and Scanning Electron Microscopy techniques. The variation of lithium-ion conductivity at room temperature as a function of the glasses’ lithium content is found to exhibit a maximum at a molar ratio of x=3.5. This maximum in the ionic conductivity is correlated to the formation of crystalline regions in the vitreous structure of the material as the lithium concentration is increased.

. In this paper, thin film bi-layers of LiCoO 2 cathode material and xLi 2 O-B 2 O 3 electrolyte glasses were prepared by e-gun evaporation. The ionic conductivity of the electrolyte films was measured by employing impedance spectroscopy technique and the results, for different chemical compositions of the electrolyte, are compared. Auger electron spectroscopy was employed to examine the successive thin-film layers of the bi-layer devices.

CCII-based electronic circuits which allow independent scaling of the voltage and current in the terminals of electronic elements are presented. The proposed circuits can compensate the nonidealities inherent in the V-I characteristics of an electronic element, thus improving the performance of the circuit in a which the element is employed. An illustrative example by PSPICE simulation shows satisfactory results.