Thermoelectric generators (TEGs) make use of the Seebeck effect in semiconductors for the direct conversion of heat to electrical energy. The possible use of a device consisting of numerous TEG modules for waste heat recovery from an internal combustion (IC) engine could considerably help worldwide efforts towards energy saving. However, commercially available TEGs operate at temperatures much lower than the actual operating temperature range in the exhaust pipe of an automobile, which could cause structural failure of the thermoelectric elements. Furthermore, continuous thermal cycling could lead to reduced efficiency and lifetime of the TEG. In this work we investigate the long-term performance and stability of a commercially available TEG under temperature and power cycling. The module was subjected to sequential hot-side heating (at 200°C) and cooling for long times (3000 h) in order to measure changes in the TEG’s performance. A reduction in Seebeck coefficient and an increase in resistivity were observed. Alternating-current (AC) impedance measurements and scanning electron microscope (SEM) observations were performed on the module, and results are presented and discussed.

Cathode powders of the Li–Mn–Ni–O system have been prepared at a Mn/(Mn+Ni) ratio varying from 0 to 1. The solid state reaction method was used to obtain the cathode materials by mixing MnO2, LiCO3 and NiO. A 20% excess of lithium was used in the precursors. The materials produced were examined by X-rays to identify their structure. Batteries were assembled by using these materials as cathode with a liquid electrolyte consisting of EC/DΜC 1:1, 1Μ LiPF6 and Li anode. Their capacity, cycle fading and charge-discharge conditions were evaluated.

. 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.

Metallic Li anode present serious problems, so we are applying the concept of an inert matrix to shield a battery anode, proposed by Huggins 15 years ago (Wang et al., 1986); Today, carbon anode based Li-ion polymer electrolyte batteries' technology is enjoying wide commercial success. However certain carbon material forms as well as liquid electrolyte interfacial (Winter et al, 1999) electrode complexities keep the anode part of the Li-ion batteries still open. Lithium alloys possess high capacity and energy densities (Wang et al., 2000). Silicon was used at elevated temperatures lithium batteries (Weydanza et al., 1999). Bulk silicon's lithiation of at room temperature presents very slow kinetics (Weydanza et al., 1999). The morphology of silicon as candidate lithium anode material seems to be a key parameter since silicon films presented good perfomance (Bourderau et al., 1999). In this work we present a new form of microcrystalline ceramic silicon prepared from pure silicon powders as candidate lithium anode at room temperature.

Lithiated spinel manganese dioxide was synthesised from electrochemical MnO2 and Li2CO3 with deficiency or excess lithium (LixMnxO4, 0.8 < x < 1.3) for use in Li/LixMn2O4 and Li-ion cells. Micron-sized Li1.05Mn2O4 prepared at 730 degrees C showed high Li utilization, excellent cyclability and good rate capability with an initial discharge capacity of 123 mA h/g and 10% discharge capacity reduction after 20 cycles. Different types of commercial carbonaceous materials were also investigated with respect to their electrochemical performance vs. Li. Unoptimised Li-ion cells, using Li1.05Mn2O4 prepared at 730 degrees C as the cathode material, EC-DMC-LiPF6 electrolyte and carbon fibres, showed promising performance characteristics. (C) 1998 Elsevier Science S.A. All rights reserved.

Magnetic properties of a series of Mg-doped granular samples were studied by means of vibrating-sample and SQUID magnetometry. The equilibrium moment measured after the sample demagnetization gave evidence that the surface barrier effects can be neglected up to 60 K. Slope of the high-field dependence was used for determination of the temperature dependence of the penetration depth and its extrapolation to T = 0, . The latter quantity was found to be significantly affected by the expression used for the data fit. The irreversible moment deduced from the magnetic hysteresis loops showed a pronounced fishtail effect. In the temperature range 50-60 K, the curve was found to scale in a similar manner as in (RE)-123 single crystals. The conventional relaxation rate dramatically changes at the fields around the remanent state. The field range of this anomaly coincides with the central peak width, and we attribute this effect to redistribution of the magnetic flux in the sample. A simple non-monotonic dependence was observed of the fishtail maximum position on the nominal Mg content. A similar but mirror dependence was found of .

The off-state current in n- and p-channel polycrystalline silicon thin-film transistors (polysilicon TFTs) is investigated systematically by conduction measurements at various temperatures and low-frequency noise measurements at room temperature. It is demonstrated that the leakage current is controlled by the reverse biased drain junction. The main conduction mechanisms are due to thermal generation at low electric fields and Poole–Frenkel accompanied by thermionic filed emission at high electric fields. The leakage current is correlated with the traps present in the polysilicon bulk and at the gate oxide/polysilicon interface which are estimated from the on-state current activation energy data. Analysis of the leakage current noise spectral density confirms that deep levels with uniform energy distribution in the silicon band gap are the main factors in determining the leakage current. The density of deep levels determined from noise analysis is in agreement with the value obtained from conductance activation energy analysis. The substantially lower leakage current observed in the n-channel polysilicon TFT is explained by the development of positive fixed charges at the interface near the drain junction which suppress the electric field.

The characterization and optimization of synthesized spinel LixMn2O4 cathode material with respect to its lithium utilization, cyclability and rate capability by controlling the synthesis conditions and the particle size of the prepared material is reported. Lithiated spinel manganese dioxide was prepared from EMD and Li containing compounds at different synthesis temperatures (450-850 degrees C) and with deficiency or excess lithium (LixMn2O4, 0.8<x<1.3). The prepared material was single phase LiMn2O4 within the range 1.1<x<1.25 while at temperatures below 730 degrees C Mn2O3 was present. Li1.05Mn2O4 prepared at 730 degrees C and ground to micron sized particles in a vibrating ball mill, showed a high initial discharge capacity (123mAh/g), excellent capacity retention (similar to 11% discharge capacity reduction after 100 cycles) and small capacity reduction for relatively high current rates (similar to 5% from C/8 to 1C).

The intercalation process of Li in molybdenum trioxide (MoO3), a layered transition metal oxide that has been proposed as candidate cathode material for rechargeable batteries, is examined in relation to the crystallinity and the growth method of the pristine material. Atomic Force Microscopy (AFM) is used for surface roughness calculations. Roughness is enhanced with intercalation at the early stages and as the process proceeds, randomly scattered domains merge into ordered clusters, and finally a fragmented surface is formed.

Single crystals of the layered structure wide band semiconductor MoO3 were grown and Al was intercalated electrochemically. Intercalation was monitored by X-ray microprobe analysis. Optical transmission measurements in the fundamental energy gap region indicate a shift of the absorption edge which is attributed to the intercalated Al species. In the vibrational spectra in the FIR region, no new peaks are observed although the relative intensity and bandwidth are modified, indicating that the chemical nature of the pristine material is not altered upon intercalation.

Indium selenide films are formed on silica slides and silicon wafers using a flash evaporation technique in which the material source stoichiometry is modified to obtain InpSeq films with various compositions. The structural and optical properties of indium selenide films are reported. These characterizations have shown that, using different growth conditions, either single phases, such as InSe, In4Se3 or In2Se3, are formed or a mixture of these compounds is present in the film structure. The products are examined by X-ray diffraction, and Raman and IR spectroscopies. The electrochemical properties of lithium-intercalated films are presented. It is observed that the morphology and stoichiometry play an important role in the lithium insertion process. The thermodynamics and kinetics of the insertion reaction are reported. Li/Li+ -borate glass/InSe microbatteries have been built, and their characteristics are reported and discussed using a Butler-Volmer relationship.

Rechargeable cells with alkali metal anode and solid solution cathode are considerably promising for high energy density batteries and micro-batteries1 based on an intercalation reaction. Under appropriate conditions a topochemical reaction of specific particles and a pre-existing structure having a large number of certain energy states may proceed as an intercalation reaction. An intercalation system exists as far as the increase in internal energy of the structure-host is less than any other non reversible process. The final criteria for the existence of an intercalation system are the observation of one (or more) single phas in the chemical potential u. vs. x, the intercalant concentration in the host -by a proper titration- and the high reversibility of the reaction. The theoretical background below an intercalation process for a lamellar host (TMD) with a high number of electron states has been developed2 and clarified3–4 already. Later on, the successful intercalation of alkali metals in more general host structures, like the 2D and 3D oxides5, presented the necessity of simultaneous consideration for ions and electrons as intercalant particles due to the limited number of electron states not far from the initial Fermi level. The origin of the “lattice gas model” for intercalation can be found in certain models of statistical mechanics for a similar to intercalants quantum assembly.

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We have investigated the electrochemical and transport properties of lithium-intercalated NiPS3. Thermodynamic and kinetic results have been obtained by the modified galvanostatic intermittent titration technique for the long-time regime in the compositional range 0 ⩽ x ⩽ 1.5. The chemical diffusion coefficient of lithium in LixNiPS3 is composition dependent and the average value is 10−9 cm2 s−1 at room temperature. The partial ionic conductivity is estimated from the experimental determination of D∗ and W and a value of σite(Li) is 2 × 10−3 ω−1 cm−1 at x = 1.0. These transport properties are compared with those obtained in a galvanic cell with a composite electrode, i.e. a mixture of active material, solid electrolyte, acetylene black and polytetrafluoroethylene. Electrochemical titration during the discharge under moderate current drain shows lower values for the transport properties in a medium which is out of equilibrium.

This work reports a study of the optical and electrical properties of tin monoselenide SnSe and tin dichalcogenides SnX2 with X = S and Se. The semiconducting character of the single crystals is investigated by means of resistivity and Hall effect in the temperature range from 90 to 300 K. The energy gap data are obtained by absorption measurements. The far-infrared reflectance spectra of the tin chalcogenide compounds have been measured. The experimental data are fitted using a four-parameter dispersion model based on the factorized form of the dielectric function.

We present a study of the transport measurements on lithium intercalated InSe single crystals. Lithium intercalant acts as a donor species and after intercalation the resistivity falls below 0.02 Ω cm with an increase in the carrier density. At low temperature pure InSe exhibits a two-dimensional conductivity owing to weak localization as a consequence of the weak disorder introduced by the large concentration of stacking faults. The logarithmic temperature dependence is found to be general and the classical formalism of the weak localization is applied. Upon intercalation the presence of Li atoms destroys the electronic interference waves and the weak localization disappears completely. The change in the electrical properties is discussed and an electronic band model is proposed.