Ac Conductivity Studies Research Articles

AC conductivity studies of silver based fast ion conducting glassy materials for solid state batteries

Glasses of various compositions of silver based fast ion conductors in the AgI–Ag 2O–( XSeO 2+(1− X)As 2O 5) (SSA) glassy system have been prepared using the melt quenching method. In the present system, the dopant salt (AgI) and network modifier (Ag 2O) contents were fixed, while the contents of the network formers ( XSeO 2+(1− X) As 2O 5) have been varied to prepare various compositions of the glassy compounds. The glassy nature of the compounds have been characterised by X-ray diffraction. The electrical conductivity measurements have been carried out at 1 kHz as well as in the frequency range of 5 Hz–13 MHz and temperature range of 295–350 K. The measured impedance data were analysed using the Boukamp equivalent circuit software and the dc (bulk) as well as frequency dependent conductivity were obtained for all the compositions of the SSA glassy compounds. Solid state batteries were fabricated using the highest conducting SSA glass with different types of cathode materials. The open circuit voltage, polarisation and discharge characteristics have been measured to estimate the life time of the batteries.

AC conductivity studies of composite polymeric electrolytes

Ac conductivity studies carried out over a temperature range of 0–100°C for polymeric electrolytes from the PEO-LiClO 4- α-Al 2O 3 system are reported. Electrolytes of various salt concentrations and containing 15 mass% α-Al 2O 3 are studied. The contribution of charge carrier concentration and ion mobility to the dc ionic conductivity of these composite polymeric electrolytes is discussed. A change in the temperature dependence of ionic conductivity is observed around the melting point of the crystalline phase of the composite electrolytes. An increase in dielectric constant following this phase transition is also observed. Above the melting temperature, an increase in the conductivity depends either on an increase in ionic mobility (samples with low salt concentration) or on the creation of charge carriers (samples with high salt concentration).

Effect of PEO addition on the electrolytic and thermal properties of PVDF-LiClO 4 polymer electrolytes

Polymer electrolyte membranes comprising poly(vinylidene fluoride), PVDF, Poly(ethylene oxide), PEO, and LiClO 4 were prepared and characterised with respect to ambient temperature ionic conductivity ( σ i). The miscibility studies were performed using XRD and DTA in order to best understand the chemical compatibility between PVDF and PEO. Structural characterisation was carried out on the polymer electrolyte thin film membranes using XRD. The ac-conductivity studies were performed to evaluate the ambient temperature conductivity of the polymer electrolyte membranes. The conductivity and mechanical integrity of PVDF:LiClO 4 polymer electrolyte complex were studied as a function of PEO concentration. The addition of PEO into PVDF:LiClO 4 complex enhances the room temperature conductivity and mechanical stability of the thin film electrolyte membrane. The maximum conductivity at 30°C was found to be 2.62×10 −5 S cm −1 for (PVDF-LiClO 4):PEO (80:20) w/o which is two orders of magnitude higher compared to PVDF-LiClO 4 system.

Electronic conduction in Bi‐modified amorphous thin films of Ge20Te80‐x Bi x exhibiting an absence of a p‐n transition

Abstract Ac conductivity and dielectric relaxation studies of well‐characterized Bi‐modified amorphous thin films of Ge20Te80‐x Bi x (x=0, 0.19, 2.93 and 7.35) prepared by flash evaporation, exhibiting an absence of p‐n transitions in the frequency range 500 Hz‐10 kHz and the temperature span 180 K‐450 K, are reported. The ac conductivity, σ ac(ω), is found to be proportional to ωs. The temperature dependences of σ ac(ω), and the exponent s are interpreted using the correlated‐barrier hopping model. It is revealed that electronic conduction takes place via bipolaron/single polaron hopping processes at low/high temperatures in all the compositions. At a lower Bi concentration (x=0.19), Bi‐induced defects that take part in single polaron hopping are produced. Further increases in the Bi concentration (x=2.93 and 7.35) cause little change in the density of such defects. The density of defect states taking part in bipolaron conduction is not significantly affected by addition of Bi atoms to the alloy. This fe...

Ac conductivity and transport studies in phosphate glasses with NASICON-type chemistry

ac conductivity studies conducted on glasses with NASICON-type chemistry reveal many universalities in their behaviour. It is found that the total conductivity of all the glasses at all temperatures can be fitted well with a double power law using s 1 = 0.5 and s 2 = 1.0. It is found that the plots of reduced conductivity (with respect to the dc conductivity) versus reduced frequency (with respect to M″ peak frequency) are superimposable for all the glasses at all temperatures, indicating that the ionic conductivity in these materials is independent of a number of factors like the nature and concentration of the cation and structure of the glass.

Ac and dc conductivity study of natural zeolitic material of the clinoptilolite type and its iodine forms

Natural zeolitic material of the clinoptilolite type and its iodine forms have been investigated by X-ray powder diffractometry, IR, X-ray photoelectron spectroscopy, thermal analysis and ac-dc conductivity as well as by EMF measurements. The ac conductivity of the natural zeolitic material was measured in the temperature range from 20 to -25°C at different relative humidities (75 to 11%). The conductivity of the iodine forms (10 −5 S cm −1, on average, at 20°C and 53%RH) was one order of magnitude higher than that of the natural zeolitic material, and turned out to be dependent on the iodine content. XPS measurements showed that the iodine forms contain iodine ions and other iodine species (I 2 and/or I − 3 ions) which are removed by heating at 200°C. Conductivity measurements, carried out before and after heating at 200°C, indicated that the presence of iodine species on the surface of the particles is probably responsible for the higher conductivity of the iodine forms. The electronic conductivity of the iodine forms, as well as that of the natural zeolitic material, was found to be negligible in comparison with ionic conductivity.

High-temperature conductivity study on single-crystal C60

We report about dc, ac (100Hz≦v≦100kHz) and contactless microwave (10 GHz) conductivity studies on C60 crystalline bulk material from room temperature to 850 K. The high temperature regime is governed by an activated behavior with a frequency and sample independent activation energy of about 0.9 eV. The low temperature regime exhibits a frequency dependent and weakly temperature dependent conductivity due to extrinsic properties.

Application of the “universal power law” to the studies of ac conductivity of polymeric electrolytes

The universal power law describing the relation between dc and ac conductivities is applied to the data obtained for various polymeric electrolytes. Changes of activation energy of conduction, hopping rate, activation energy for ion hopping and activation energy of charge carriers creation are analyzed according to the West-Almond formalism. The obtained results are correlated with the phase structure of the polymeric electrolyte and its ambient temperature ionic conductivity. We find that high conductivity values are measured for systems for which the activation energy of ion hopping is considerably lower compared to the activation energy of charge carrier's creation.

Electrical Properties of Silver‐Doped As2S3

AbstractTemperature and frequency dependent ac conductivity studies are made for silver‐doped a‐As2S3. The temperature dependence of σac for the As2S3‐Ag system can be well explained by correlated barrier hopping model. Numerical calculations agree well with the experimental results. The energy levels and the concentration of charged defects are also estimated for these materials.

A zinc trifluoromethane sulphonate polymer electrolyte

Conductivity, transport and interfacial studies on an amorphous methoxy-linked poly(ethylene oxide)/Zn(CF 3SO 3) 2 system over the O:Zn range 100:1 to 10:1 are reported. A passivating layer on the zinc electrode has been studied and a convenient technique of electrochemical polishing has been devised to reduce its impedance. Standard ac conductivity and DSC studies have been supplemented by dc polarization measurements using the symmetric cell Zn|polymer electrolyte|Zn. Preliminary results of transference number determination using the Hittorf method suggest that transport of zinc in a concentration gradient is augmented by motion of neutral ionic complexes.

Ac conductivity and dielectric relaxation studies in AgI-based fast ion conducting glasses

ac conductivity and dielectric relaxation in AgI-based fast ion conducting glasses have been examined in four systems: AgI-Ag 2MoO 4, AgI-Ag 3AsO 4, AgI-AgPO 3 and AgI-Ag 2O-V 2O 5. Dielectric relaxation is examined using modulus formalism. Suitability of stretched exponential relaxation function has been investigated. Inverse relation has been found to exist between the stretching exponent and the structural unpinning number which characterizes fast ion conduction. Physical origin of correlated states, relevance of cluster-tissue model of glasses and the role ofstructural unpinning concept have been examined in the light of dielectric behavior of AgI-based glassy fast ion conductors.

Super ionic conduction in alkali metal hexachloro niobates and tantalates

ac-conductivity, DSC, and neutron diffraction studies of the ionic conductors KNbCl 6 and KTaCl 6 are presented. The first order phase transitions to the super ionic state occur at temperatures in the range 299–334°C. Conductivities up to 0.35 S/cm are observed. The lowest transition is from a hexagonal to a cubic fcc structure, whereas no definite conclusions could be drawn concerning the structure of the super ionic phases, since only three diffraction peaks were observed in the diffractograms.

Magnetotransport studies in charge density wave conductors

We have performed transport studies on the lower charge density wave (CDW) state of NbSe 3 in the presence of applied magnetic (H) fields of up to 75 kG. Dc conductivity and narrow band noise measurements show that the spectacular magnetoresistance which occurs in the lower CDW state is associated with conversion of normal carriers into CDW carriers. Ac conductivity studies indicate that the CDW continues to behave overdamped in an H-field, but the crossover frequency increases. These results are compared to the predictions of Balseiro and Fallicov for an anistropic system with imperfect nesting.

Ac Conductivity and conductivity relaxation studies in the CeO 2−Y 2O 3 system

The electric modulus and ac conductivity of CeO 2−Y 2O 3 solid solutions were studied as a function of Y 2O 3 concentration (0.05 to 20 m/o Y 2O 3) and temperature (∽400–650 K). A minimum relaxation time and maximum conductivity were identified at ∽ 3 m/o Y 2O 3 in CeO 2.

EPR and AC conductivity studies of the structural phase transition in CsCuCl3

EPR and AC conductivity data on CsCuCl3 single crystals are reported for the temperature range from 291 to 465K. The spectroscopic behaviour of the g-factor versus temperature has been explained by hypothesising that, for T<or=351K, Cu2+ ions are in effect tetrahedrally coordinated, while, in the temperature range 351<or=T<or=420K, they are octahedrally coordinated with an associated evolution from the static to the dynamic Jahn-Teller effect. Above 420K a single g EPR signal is observed. Support for such an interpretation is given by AC conductivity data which show, in the same temperature ranges, three thermally activated behaviours characterised by different activation energies.

Experimental study of the three-dimensional ac conductivity and dielectric constant of a conductor-insulator composite near the percolation threshold.

We measured the ac conductivity and dielectric constant of a three-dimensional randomly mixed conductor-insulator system consisting of amorphous carbon and Teflon powder in the frequency range from 10 Hz to 13 MHz. Near the percolation threshold, these two quantities varied as a power of \ensuremath{\omega}, such as \ensuremath{\sigma}\ensuremath{\sim}${\ensuremath{\omega}}^{x}$, and \ensuremath{\epsilon}\ensuremath{\sim}${\ensuremath{\omega}}^{\mathrm{\ensuremath{-}}y}$. The values of x and y were found to be 0.86\ifmmode\pm\else\textpm\fi{}0.06 and 0.12\ifmmode\pm\else\textpm\fi{}0.04, respectively. These values are compared to the present percolation theories. We also measured the dc conductivity exponent t and dielectric constant exponent s to complete the study. Our data yielded t=1.85\ifmmode\pm\else\textpm\fi{}0.25 and s=0.68\ifmmode\pm\else\textpm\fi{}0.05.

AC conductivity, calorimetric, X-ray, and Raman study of the hexagonal phase TlInS2-III

X-ray, calorimetric, and Raman studies show definitely that black hexagonal TlInS2-III is stable from 20 to 785 K, whereas the yellow monoclinic TlInS2-I exists as solid at temperatures from 785 K to the melting point (1050 ± 5 K). Yellow TlInS2-I can be obtained in a metastable state also at room temperature and is transformed irreversibly into TlInS2-III by annealing. The transformation of TlInS2-I into TlInS2-III leads to a change in the electric conductivity, which is about three orders of magnitude higher in the hexagonal phase. The activation energies of the conductivity in the monoclinic and hexagonal phase are (133 ± 10) and (184 ± 5) meV, respectively. The Raman measurements support the space group assignment (P63/mm c  D6h4) of TlInS2-III. Röntgen-, kalorimetrische und Ramanuntersuchungen zeigen definitiv, daß schwarzes hexagonales TlInS2-III von 20 bis 785 K stabil ist, während das gelbe monokline TlInS2-I als Festkörper bei Temperaturen von 785 K bis zum Schmelzpunkt (1050 ± 5 K) existiert. Gelbes TlInS2-I kann im metastabilen Zustand auch bei Zimmertemperatur erhalten werden und wird durch Tempern irreversibel in TlInS2-III transformiert. Der übergang von TlInS2-I in TlInS2-III führt zu einer änderung der elektrischen Leitfähigkeit, die etwa drei Größenordnungen höher ist in der hexagonalen Phase. Die Aktivierungsenergien der Leitfähigkeit in der monoklinen und hexagonalen Phase betragen (133 ± 10) bzw. (184 ± 5) meV. Die Ramanmessungen bestätigen die Zuordnung von TlInS2-III zur Raumgruppe (P63/mm c  D6h4).

Electrical transport studies in AsSe glasses

The DC and AC conductivity studies of AsSe glasses over a wide range of compositions have been reported and discussed. The contribution to conductivity from transport among extended states has been delineated and the possible existence of a characteristic temperature is indicated. Two conductivity maxima have been observed as a function of composition in AC conductivities at lower temperatures.

Numerical studies of the AC conductivity of hopping systems. I. Effects of space and energy disorder

Results are presented of exact numerical calculations of the AC conductivity of a simple, physically useful model of a hopping system. The model consists of a finite one-dimensional lattice of sites with the carrier hopping by a phonon assisted process between states localized on the lattice sites. It is shown that the frequency dependence of a finite lattice of regularly spaced sites of equal energy is of the Debye type, with a 'relaxation time' which can be related to the transit time of a carrier along the finite chain. For a lattice of equal energy sites randomly distributed in space, the conductivity saturates at high frequency and at lower frequencies can be represented by sigma ( omega )=A omega s, where s<or approximately=1. For a regular lattice of sites with a random distribution of energy levels, similar frequency dependence is observed with the value of s changing systematically with temperature.

Transition from Ionic to Electronic Conduction in Pure ThO2 Under Reducing Conditions

Open‐circuit emf and ac conductivity studies were conducted on two batches of dense polycrystalline ThO2. The open‐circuit emf data were used to delineate the low‐po2 ionic domain boundary for “pure” ThO2, which is presented as a log Pθ line on a log Po2‐1/T diagram. In addition the ionic conductivity, σion, and the high‐Po2 log Pθ boundary were also determined, mainly from ac conductivity measurements, which also confirmed the Po2I/4 dependence of σp, the p‐type electronic conductivity, shown by other investigators. The main results are, for the first batch, log Pθ= 12.7−220.2 × 103/4.575T, log σion= 1.9−44.3×103/4.575T, and log Pθ=−1.0−31.4 × 103/4.575T; for the second batch, log Pθ=11.2−219.7 × 103/4.575T, log σion= 1.7−41.6 × 103/4.575T, and log Pθ=0.6−40.4 × 103/4.575T. The oxygen permeability of ThO2 tubes and the oxidation rate constant of Th were predicted from the conductivity and emf data and compared with direct measurements previously reported. The calculated and previously measured permeabilities agreed very well; however, the correlation between the predicted and previously measured oxidation kinetics was somewhat less satisfactory.