Conductivity studies of lithium zinc silicate glasses with varying lithium contents

The electrical conductivity of lithium zinc silicate (LZS) glasses with composition, (SiO₂)_0.527 (Na₂O)_0.054(B₂O₃)_0.05(P₂O₅)_0.029(ZnO)_0.34−x (Li₂O) _x (x = 0.05, 0.08, 0.11, 0.18, 0.21, 0.24 and 0.27), was studied as a function of frequency in the range 100 Hz–15 MHz, over a temperature range from 546–637 K. The a.c. conductivity is found to obey Jonscher’s relation. The d.c. conductivity (σ _d.c.) and the hopping frequency (ω _h), inferred from the a.c. conductivity data, exhibit Arrhenius-type behaviour with temperature. The electrical modulus spectra show a single peak, indicating a single electrical relaxation time, τ, which also exhibits Arrhenius-type behaviour. Values of activation energy derived from σ _d.c., ω _h and τ are almost equal within the experimental error. It is seen that σ _d.c. and ω _h increase systematically with Li₂O content up to 21 mol% and then decrease for higher Li₂O content, indicating a mixed alkali effect caused by mobile Li⁺ and Na⁺ ions. The scaling behaviour of the modulus suggests that the relaxation process is independent of temperature but depends upon Li⁺ concentration.     

Fast ion conducting lithium glasses—Review

For the last few years fast ion conducting lithium glasses are being studied due to their potential use in advanced electrochemical devices. A number of glass systems containing oxides, sulphides and other lithium compounds prepared by both conventional cooling and rapid quenching techniques have been reported. In this paper we review the transport properties of lithium ion conducting glasses. The special features of the ionic conduction process have been highlighted and some experimental techniques to study transport properties have been described. Some of the common observations of the properties have been discussed and finally some important problems for future development have been pointed out.     

Near ideal electrical switching in fast ion conducting glasses: Evidence for an electronic process with chemical origin

Bulk AgI based fast ion conducting (FIC) glasses have been prepared by a novel microwave technique. Electrical switching characteristics of these glasses have been investigated for the first time. It has been found that AgI based FIC glasses exhibit a current-controlled high speed memory electrical switching behaviour. SEM, EDAX and ESR investigations have been performed on the virgin and switched sampies to understand the nature of the conducting state. A chemical model is proposed to explain the switching behaviour of these glasses, which is consistent with the observed results.     

Deposition temperature effect on the electric and dielectric properties of InSbSe3 thin films

Thin films of InSbSe₃ compound were obtained by thermal evaporation on to clean glass substrates maintained at various deposition temperatures from 423 to 593 K. At deposition temperature T_d?473 K, the films have an amorphous structure, while those prepared at T_d>473 K have a polycrystalline structure identified by X-ray diffraction analysis. The DC electrical conductivity of the films increases as T_d increases, whereas activation energy decreases with increasing T_d, which reflects a change in the degree of disorder. AC conductivity was studied as a function of frequency in the range (10²-10⁵ Hz) and as a function of deposition temperature. The dependence of T_d on the frequency exponent s in the conductivity-frequency relation confirmed that the mechanism of AC conductivity is correlated barrier hopping with a single polaron hopping mechanism. The discrepancy between DC and AC activation energies was studied as a function of deposition temperature. The maximum barrier height W_m and the density of defect states N were also determined. Finally, the dependence of dielectric constant and dielectric loss on T_d were studied. A Debye-like relaxation of dielectric behavior was observed for crystalline films and is found to be a thermally activated process. The position of maximum dielectric loss is shifted towards higher temperature with T_d treatment and there by reduces the relaxation time.     

Li<Superscript>+</Superscript> ion conductivities in boro-tellurite glasses

Lithium ion conductivity has been investigated in a boro-tellurite glass system, LiCl.LiBO₂.TeO₂. In the absence of LiCl, the conductivity increases with increasing non-bridging oxygen (NBO) concentration. LiCl addition has little influence on total conductivity although the observed barriers are low. Formation of LiCl clusters appears evident. In the a.c. conductivity and dielectric studies, it is observed that the conductivity mechanism remains the same in all compositions and at all temperatures. A suggestion is made that Li⁺ ion transport may be driven by bridging oxygen ↔r non-bridging oxygen (BO ↔r NBO) switching, which is why the two different types of Li⁺ ions in the clusters and in the neighbourhood of NBOs, do not manifest in the conductivity studies.     

A new approach for understanding ion transport in glasses; example of complex alkali diborate glasses containing lead, bismuth and tellurium oxides

Mechanism of ion transport in glasses continues to be incompletely understood. Several of the theoretical models in vogue fail to rationalize conductivity behaviour when d.c. and a.c. measurements are considered together. While they seem to involve the presence of at least two components in d.c. activation energy, experiments fail to reveal that feature. Further, only minor importance is given to the influence of structure of the glass on the ionic conductivity behaviour. In this paper, we have examined several general aspects of ion transport taking the example of ionically conducting glasses in pseudo binary, yNa₂B₄O₇·(1?y) M _a O _b (with y = 0·25–0·79 and M _a O _b = PbO, TeO₂ and Bi₂O₃) system of glasses which have also been recently characterized. Ion transport in them has been studied in detail. We have proposed that non-bridging oxygen (NBO) participation is crucial to the understanding of the observed conductivity behaviour. NBO–BO switching is projected as the first important step in ion transport and alkali ion jump is a subsequent event with a characteristically lower barrier which is, therefore, not observed in any study. All important observations in d.c. and a.c. transport in glasses are found consistent with this model.     

Electronic transport and optical properties of thin oxide films

In this work, we present optical characterization of films of two transparent conductive oxides (ITO: indium tin oxide and ZnO: zinc oxide) including absorption coefficient and optical gap energy. We have also investigated the transport properties of ITO and ZnO films through measurements of electrical conductivity and thermoelectric power versus temperature. These measurements enabled us to investigate conduction mechanisms for metal-nonmetal transitions. Undoped ZnO thin films show a metal-semiconductor transition at temperatures beyond 350 K. We have conducted a similar study on ITO films where we demonstrated, for the first time, the existence of a conductivity transition below 400 K, which indicates a high absolute thermoelectric power at temperatures above the transition temperature.     

Relaxation processes in a glassy polymer containing methanol molecules

The interaction of small guest molecules with the molecular degrees of freedom of a glassy polymer matrix is investigated, i.e. (i) the dynamics of these guest molecules and (ii) their effect on the secondary ‘β’ and main ‘’ relaxations of the host polymeric matrix. The system considered here is the glassy poly(methyl metacrylate) modified by introduction and desorption of methanol. The dynamics of the system is observed by means of low-frequency mechanical and wide band dielectric spectroscopies. The presence of small molecules in the PMMA glassy matrix induces several effects, namely (i) a strong relaxation peak develops at low temperature (near 120 K at 1 Hz and called _m in the following), (ii) the strength of the β relaxation is increased while the temperature of the maximum shifts towards the low temperatures, (iii) a sharp peak appears superimposed on the β peak, and finally (iv) the relaxation shifts towards the low temperatures. Dielectric and mechanical spectroscopies results are in agreement and make it possible to capture the dynamical behavior in a wide frequency range (eight decades). The experimental results are explained on the basis of physical concepts recently introduced in the physics of glassy matter: cooperativity and nanoheterogeneity. In particular, the low-temperature relaxation process _m is attributed to cooperative motions in methanol clusters which form in the nanoheterogeneous polymeric matrix, in agreement with small angle X-rays scattering and low-frequency Raman scattering observations recently reported.     

Non-ohmic transport behavior in ultra-thin gold films

Structure and local lateral electrical properties of Au films of thicknesses ranging from 10 to 140 nm are studied using conductive atomic force microscopy. Comparison of current maps taken at different thicknesses reveals surprising highly resistive regions (10¹⁰-10¹¹ Ω), the density of which increases strongly at lower thickness. The high resistivity is shown to be directly related to discontinuities in the metal sheet. Local I-V curves are acquired to show the nature of electrical behavior relative to thickness. Results show that in Au films of higher thickness the electrical behavior is ohmic, while it is non-ohmic in highly discontinuous films of lower thickness, with the transition happening between 34 and 39 nm. The non-ohmic behavior is explained with tunneling occurring between separated Au islands. The results explain the abrupt increase of electrical resistivity at lower thin film thicknesses.     

Electrical properties of glasses in the Na2O–MoO3–P2O5 system

A range of coloured electronic or mixed ionic–electronic glasses has been evidenced in the Na₂O–MoO₃–P₂O₅ system. The properties of these glasses have been studied along different composition lines corresponding either to a fixed Na₂O content or a constant Mo/P ratio. An EPR spectroscopy investigation of these glasses has allowed to determine the Mo⁵⁺ ion percentages in these materials. The electrical properties of these glasses have been studied by impedance spectroscopy, and the electronic and ionic contributions have been evaluated. The properties of these sodium glasses have been compared with those of lithium glasses with the same compositions.     

Coupling of conductivity to the relaxation process in polymer electrolytes

Conductivity relaxation using modulus formalism has been used to explore the coupling of ionic conductivity to dielectric relaxation in polymer electrolyte based on polyethylene oxide complexed with various content of LiAsF₆. The temperature dependence of conductivity followed the VTF behavior suggesting close correlation between conductivity and the segmental relaxation process in polymer electrolytes. The coupling of conductivity to the segmental process has been discussed in terms of coupling index. For all compositions studied, the coupling index was within the range of 1–11 in the temperature range of investigation, which was in agreement with the coupled systems.     

Copper substitutions in synthetic miargyrite α-AgSbS2 mineral: Synthesis,characterization and dielectrical properties

The nominal compositions Ag_0.8Cu_0.2SbS₂ and Ag_0.7Cu_0.3SbS₂ have been synthesized by conventional ceramic solid-state reaction at high temperature. X-ray diffraction (XRD) and scanning electron microscopy chemical analysis (SEM-EDAX) revealed single phases, isostructural to the natural miargyrite α-AgSbS₂ mineral. Examination of the lattice parameters shows a decrease in the cell volume with increasing copper substitutions. The Raman analysis displays absorptions which may be assigned to the Sb–S stretching vibrations of the SbS₃ pyramids. The impedance-frequency analysis showed grain boundary and electrode interface contributions in non-Debye type relaxation, following Jonscher's universal power law. The giant permittivity response is attributed to extrinsic effects without evidence of a ferroelectric transition. Summerfield scaling, leading to the superposition of impedance analysis, implies that the relaxation is thermally activated, without introducing more than one underlying transport mechanism.     

聚合物电解质膜中离子输送过程的模拟理论

综述了离子在聚合物电解质中输送过程的模拟,讨论了电解质中动态键渗透理论、格子重排扩散模型、一维跃迁模型等基本的模拟方法及其主要特点．     

Studies on the electronic transport properties of some organic semiconductors in thin films

The investigated compounds are some derivatives of orthotolidin-N,N-bis (4-aminobenzene-2-sulphonic) acid. The temperature dependences of the electrical conductivity and Seebeck coefficient are studied on the thin films deposited from dimethylformamide solution onto glass substrates. It is known that the investigated compounds have typical semiconducting properties. The values of some important parameters of the films (thermal activation energy of electrical conduction, concentrations and mobilities of charge carriers) have been determined. The correlations between some of these parameters and molecular structure of the respective compounds are discussed.     

Spectroscopic and transport studies of Cu2+ ion doped in (40 —x)Li2O—xLiF—60Bi2O3 glasses

The preparation of (40-x)Li₂O-xLiF-60Bi₂O₃ glassy system and spectroscopic and transport studies of this system are reported. IR results show that this glass consists of [BiO₃] units and indicate formation of Bi-F bonds with the addition of LiF. From the ESR spectra of Cu²⁺ ion, the effectiveg values are found to vary slightly with increasing concentration of fluorine ion. The optical absorption peak corresponding to Cu²⁺ increased linearly with increasing concentration of LiF between 620 nm and 728 nm except at 2.5 mole% of LiF where its value is 729 nm. This peculiar behaviour is attributed to the varying structural coordination of fluorine as the concentration of lithium fluoride is increased. The ionic conductivity measurements indicate that the conduction is due to adiabatic hopping of polarons and the activation energies are found to be temperature and concentration dependent     

Charge carrier transport in Cu(COOH)2 organic molecular single crystal

The temperature dependences of the d.c. electrical conductivity (σ) and thermoelectric power (TEP) of low-dimensional Cu(COOH)₂ single crystal have been studied. The electrical conductivity is highly anisotropic (σ_‡/σ = 3.0 × 10²) and the crystal undergoes a Peierls transition at 208 K and two polymorphous phase transitions, namely → β and β → at 327 and 377 K respectively. The conductivity in this crystal is found to be mainly due to a non-adiabatic hopping mechanism. TEP measurements carried out at various temperatures show that the conductivity is due to the mobility of holes.     

Preparation and mobile ion transport studies of Ta and Nb doped Li6Zr2O7 Li-fast ion conductors

Pure and doped Li_6−x(Zr_2−xM_x)O₇, M = Nb and Ta; x = 0, 0.15 compounds have been prepared by the urea combustion method followed by annealing at 950 °C for 8 h. The samples are characterized by X-ray diffraction and impedance spectroscopy. Ionic conductivities, σ_ionic, were determined in the temperature range of 60-360 °C by impedance spectroscopy. We observe that the Ta doped Li₆Zr₂O₇ has a measurable σ_ionic at ∼160 °C, and at 300 °C exhibits a conductivity value of 1 × 10⁻³ S/cm. The temperature dependence of the conductivity in the range 100-360 °C obeys an Arrhenius relation, yielding an activation energy of E_a = 0.95 eV (for M = Ta and x = 0.15).The bond valence approach has been used to visualise Li⁺ ion migration pathways and the conductivity mechanism in these compounds. The lowest energy pathway is found to extend along the [0 1 2] direction. The Bond valence analysis also indicates a significantly anisotropic Li-ion conductivity in compounds with Li₆Zr₂O₇ type structure, predicting activation energies of 1.1 and 0.9 eV for the low energy pathway in undoped and doped Li₆Zr₂O₇.     

Study of electronic transport properties of some new N-(p-R-phenacyl)-1,7-phenanthrolinium bromides in thin films

The electrical conductivity (σ) and thermoelectric power (S) of six newly synthesized high resistivity organic salts, N-(p-R-phenacyl)-1,7-phenanthrolinium bromides (T compounds), were investigated as a function of temperature.     

Density effects in internal-energy transport in polyatomic gases

The revised Enskog theory is used in a heuristic way to modify the Wang Chang-Uhlenbeck quantum kinetic equation for polyatomic gases close to thermodynamic equilibrium. The density effects predicted for the total and internal thermal conductivities are in qualitative agreement with recent molecular dynamic calculations, suggesting that inelastic effects should be included in dense fluid transport theory. Paper dedicated to Professor Edward A. Mason.     

Enhancement in electrical conductivity of Li<Subscript>2</Subscript>O: B<Subscript>2</Subscript>O<Subscript>3</Subscript>: V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The study of electrical conductivity of 30Li₂O: (70 − x) B₂O₃: xV₂O₅ glass samples has been carried out. The results have been explained by dividing the temperature range into two regions. In region I, conductivity shows Arrhenius behaviour for all the samples. The conductivity increases with addition of V₂O₅. The results have been explained in the light of Anderson and Stuart Model. In region II, an anomalous enhancement in the conductivity is observed for all the samples up to certain temperature beyond which the conductivity decreases. The enhancement in the conductivity in the annealed glass sample has been attributed to nanocrystallization.