Decrease In Dc Conductivity Research Articles

Effect of TeO2 Addition on the Mobility of Silver Ions in Ag2O-B2O3-P2O5-TeO2 Glasses

The effect of adding TeO2 into (100-x)[0.5Ag2O−0.1B2O3−0.4P2O5]−xTeO2 glasses, with 0−80 mol% TeO2, on the structural changes and electrical properties has been investigated. The structure was studied by Raman spectroscopy and electrical properties have been studied over a wide temperature and frequency range by impedance spectroscopy. The addition of the third glass former, TeO2, to the glass network causes the structural transformation from TeO3 (tp) to TeO4 (tbp) which contributes to the changes in conductivity. The glasses with low TeO2 content show only a slow decrease in dc conductivity with addition of TeO2 due to the increase of the number of non-bridging oxygens, which increases the mobility of Ag+ ions. The steep decrease in conductivity for glasses containing more than 40 mol% TeO2 is a result of decrease of the Ag2O content and stronger cross-linkage in glass network through the formation of more Te-eqOax-Te bonds in TeO4 tbp units. The glasses obey scaling of the ac conductivity with respect to temperature indicating that the dynamic process is independent of temperature. However, the scaling of the spectra for different glasses revealed deviations from the Summerfield scaling due to the local structural disorder caused by structural transition in tellurite glass network.

Effect of substituting iron on structural, thermal and dielectric properties of lithium borate glasses

Glasses with composition xFe2O3·(30−x)Li2O·70B2O3 (x=0, 2, 5, 7 and 10mol%) were prepared via melt-quenching technique and their physical, thermal and dielectric properties are discussed. XRD was carried out to confirm the amorphous nature of prepared glasses. Density (ρ) and molar volume (Vm) were found to increase with increase in Fe2O3 content. Infrared absorption spectra depicted that Fe2O3 is acting as a network modifier. DTA has been carried out to determine glass transition temperature (Tg) and crystallization temperature (Tx). Electrical properties have been studied using impedance spectroscopy and dc conductivity. The dc conductivity decreases and activation energy increases on replacing Li+ ions with Fe3+. The impedance measurements reveal that the total conductivity obeys Jonscher’s power law. Study of the equivalent circuit analysis up to a temperature of 523K shows a significant change in the equivalent circuitry with change in temperature and composition.

Electrical mobility of silver ion in Ag2O-B2O3-P2O5-TeO2 glasses.

The effect of adding TeO(2) into (100 - x)[0.5Ag(2)O - 0.1B(2)O(3) - 0.4P(2)O(5)] - xTeO(2), with 0-80 mol % TeO(2) glass, on the structural changes and electrical properties has been investigated. DSC and thermodilatomery were used to study their thermal behavior, structure was studied by Raman spectroscopy, and electrical properties have been studied by impedance spectroscopy over a wide temperature and frequency range. The introduction of TeO(2) as a third glass former to the glass network causes the structural transformation from TeO(3) (tp) to TeO(4) (tbp) which contributes to the changes in conductivity. The glasses with low TeO(2) content show only a slow decrease in dc conductivity with addition of TeO(2) due to the increase of the number of nonbridging oxygens, which increases the mobility of Ag(+) ions. The steep decrease in conductivity for glasses containing more than 40 mol % TeO(2) is a result of decrease of the Ag(2)O content and stronger cross-linkage in glass network through the formation of more Te-(eq)O(ax)-Te bonds in TeO(4) tbp units. The glasses obey ac conductivity scaling with respect to temperature, implying that the dynamic process is not temperature dependent. On the other hand, the scaling of the spectra for different glass compositions showed the deviations from the Summerfield scaling because of the local structural disorder which occurs as a result of the structural modifications in the tellurite glass network.

Effect of MoO3 on electron paramagnetic resonance spectra, optical spectra and dc conductivity of vanadyl ion doped alkali molybdo-borate glasses

Alkali molybdo-borate glasses having composition xMoO3·(30−x)M2O·70B2O3 and xMoO3·(70−x)B2O3·30M2O (M=Li, Na, K) with 0⩽x⩽15 (mol%) doped with 2.0mol% of V2O5 have been prepared in order to study the influence of MoO3 on electrical conductivity, electron paramagnetic resonance (EPR) and optical spectra. From EPR studies it is observed that V4+ ions in these samples exist as VO2+ ions in octahedral coordination with a tetragonal compression and belong to C4V symmetry. The tetragonal nature and octahedral symmetry of V4+O6 complex increase as well as decrease depending upon the composition of glasses with increase in MoO3 but 3dxy orbit of unpaired electron in the VO2+ ion expands in all the glasses. The decrease in optical band gap suggests that there is an increase in the concentration of non-bridging oxygen’s. From the study of optical transmission spectra it is observed that for all the glasses the degree of covalency of the σ-bonding decreases with increase in MoO3 content and the degree of covalency of the π-bonding also varies. These results based on optical spectroscopy are in agreement with EPR findings. It is found that dc conductivity decreases and activation energy increases with increase in MoO3:M2O (M=Li, Na, K) ratio in MoO3·M2O·B2O3 glasses, whereas the conductivity increases and activation energy decreases with increase in MoO3:B2O3 ratio in xMoO3·B2O3·M2O glasses, which is governed by the increase in nonbridging oxygen’s. The variation in theoretical optical basicity, Λth is also studied.

Local atomic structure and electrical properties of Ge20Se80−xTex (x=0, 5, 10, and 15) glasses doped with Ho

Abstract Measurements of ac and dc conductivities, complex electrical modulus, static permittivity, dielectric relaxation, and X-ray diffraction of the glassy system Ge20Se80−xTex (x = 0, 5, 10, and 15), “pure” and doped with 1000–2000 wt.-ppm Ho (added as metal or oxide), are presented and discussed. Influence of crystallization and/or phase separation on these properties is described. Temperature dependences of the dc conductivity are Arrhenius-like; their conduction activation energy increases (0.73–0.84 eV) and the dc conductivity decreases (1.5×10−6−8×10−8 S/m, at 60 °C) with decreasing concentration of Te. Doping with Ho3+ ions in a metallic form decreases the conduction activation energy. Relative static permittivity of glasses ranges from 9.6 to 12.8. The highest values are found in heavily doped, partly crystallized glasses. The lowest values are found in “pure” glasses with a high content of Te. At 1000 wt.-ppm Ho, modular diagrams are almost semicircular, modular spectra are Debye-like, and their shape is independent on temperature. At 2000 wt.-ppm Ho, two relaxation processes appear and the shape of both modular diagrams and modular spectra depend on temperature. A partial crystallization takes place in these glasses. For heavily doped glasses (1500 and 2000 wt.-ppm Ho), XRD experiments, using high-energy photons, show distinct Bragg peaks stemming from a tiny fraction (about 0.25%) of crystalline phases. Crystalline component is rather homogeneously distributed within the sample. Changing level of Ho doping affects the short-distance arrangement in glasses. A higher level of Ho doping implies shortening of the inter-atomic distances, higher mean atomic density, and higher coordination numbers what suggests better atomic packing.

Li+ ion conduction mechanism in poly (ε-caprolactone)-based polymer electrolyte

In this work, solid polymer electrolytes based on poly(ɛ-caprolactone) (PCL) with lithium bis(oxalato)borate as a doping salt were prepared by solution cast technique using DMF as a solvent. The electrical DC conductivity and dielectric constant of the solid polymer electrolyte samples were investigated by electrochemical impedance spectroscopy over a frequency range from 50 Hz to 1 MHz. It was found that the DC conductivity increased with increase in the salt concentration to up to 4 wt% and thereafter decreased. Dielectric constant versus salt concentration was used to interpret the decrease in DC conductivity with increase in salt concentration. The DC conductivity as a function of temperature follows Arrhenius behavior in low temperature region, which reveals that ion conduction occurs through successful hopping. The curvature of DC conductivity at high temperatures indicates the contribution of segmental motion to ion conduction. High values for dielectric constant and dielectric loss were observed at low frequencies. The plateau of dielectric constant and dielectric loss at high frequencies can be observed as a result of rapid oscillation of the AC electric field. The HN dielectric function was utilized to study the dielectric relaxation. The experimental and theoretical data of dielectric constant are very close to each other at low temperatures. At high temperatures, the simulated data are more deviated from the experimental curve of dielectric constant due to the dominance of electrode polarization. The non-unity of relaxation parameters (α and β) reveals that the relaxation processes in PCL-based solid electrolyte is a non-Debye type of relaxation.

Non-Ohmic and dielectric properties of CaCu3Ti4O12-MgO nanocomposites

Graphical abstractDisplay Omitted Highlights? Addition of 5vol.% MgO can improve dielectric and nonlinear properties of CCTO. ? The low-frequency tan? of CCTO-MgO (5vol.%) was greatly reduced. ? e' of CCTO-MgO (5vol.%) is higher than 104 in the frequency range of 102-105Hz. ? Addition of 5vol.% MgO can enhance breakdown voltage and nonlinear coefficient. In this work, CaCu3Ti4O12-xMgO (x=0, 5, and 10vol.%) nanocomposites were prepared by a conventional mixed oxide method using CaCu3Ti4O12 and MgO nanopowders with particles sizes of about 100-300nm and 36-50nm, respectively. The dielectric and electrical properties of CaCu3Ti4O12 and CaCu3Ti4O12/MgO ceramics were investigated. The results revealed that addition of 5vol.% MgO can improve both dielectric and electrical nonlinear properties. The low-frequency loss tangent was greatly reduced; while, the dielectric constant was found to be higher than 104 in the frequency range of 102-105Hz. The decrease in a low-frequency loss tangent is caused by a decrease in DC conductivity. Addition of 5vol.% MgO can also enhance significantly the breakdown voltage and nonlinear coefficient of CaCu3Ti4O12 ceramic. Using impedance spectroscopy analysis, the increase in the breakdown voltage is attributed to an increase in the resistance of grain boundaries.

Synthesis, structural, optical and electrical properties of metal nanoparticle–rare earth ion dispersed in polymer film

Cu-nanoparticles have been prepared by ablating a copper target submerged in benzene with laser pulses of Nd:YAG (wavelength: 355, 532 nm and 1,064 nm). Colloidal nanoparticles have been characterized by UV–Vis spectroscopy and transmission electron microscopy. The obtained radius for the nanoparticles prepared using 1,064 nm irradiation lies in the range 15–30 nm, with absorption peak at 572 nm. Luminescence properties of Tb3+ ions in the presence and absence of Cu-nanoparticles have been investigated using 355 nm excitation. An enhancement in luminescence of Tb3+ by local field effect causing increase in lifetime of 5D4 level of Tb3+ ion has been observed. Frequency and temperature-dependent conductivity of Tb3+ doped PVA thin films with and without Cu-nanoparticles have been measured in the frequency range 20 Hz–1 MHz and in the temperature range 318–338 K (well below its melting temperature). Real part of the conductivity spectra has been explained in terms of power law. The electrical properties of the thin films show a decrease in dc conductivity on incorporation of the Cu-nanoparticles.

Microstructure and modified giant dielectric response in Ga‐doped La1.5Sr0.5NiO4 ceramics

The aim of this work is to improve the dielectric properties of giant permittivity La1.5Sr0.5NiO4 ceramics. The microstructure and dielectric properties of Ga‐doped La1.5Sr0.5NiO4 ceramics prepared by a solid state reaction method were investigated. It was found that Ga3+ doping ions have a remarkable influence on the microstructural evolution. La1.5Sr0.5Ni1−xGaxO4 (x=0, 0.1, and 0.3) ceramics exhibited giant dielectric constant with ε′~3.3–4.7×105 at 20°C and 1kHz. Interestingly, ε′ of La1.5Sr0.5Ni1−xGaxO4 ceramics was enhanced by doping with Ga3+; whereas, the loss tangent (tanδ) decreased significantly. Reduction of tanδ is attributed to the increase in the total resistance, which is mainly governed by the sample–electrode contact resistance, and caused by a decrease in dc conductivity.

Electrooptic and Dielectric Studies in Cadmium Sulphide Nanorods/Ferroelectric Liquid Crystal Mixtures

We present the results based on the electrooptic and dielectric studies in cadmium sulphide (CdS) nanorods/ferroelectric liquid crystal mixtures. Doping of CdS nanorods increases the spontaneous polarization and response time, which due to large dipole-dipole interaction and increase in anchoring energies exists between nanorods and FLC molecules. Dielectric measurements revealed a decrease (~40% for 0.3% CdS in FLC) in permittivity and dielectric strength in doped sample cell than pure FLC mixture. A decrease in dc conductivity and relaxation frequency with doping concentration was also noticed. The preexponent factor and fractional exponent factor are found as predicated by existing theories.

DC Conductivity and Dielectric Behaviour of Glassy Se<sub>100–x</sub>Zn<sub>x</sub> Alloy

The DC conductivity and dielectric properties of glassy Se100–xZnx 2 ≤ x ≤ 20 alloys have been investigated in the temperature range 303 - 487 K with frequency range 100 Hz – 1 MHz. It is observed that DC conductivity decreases and the activation energy increases with Zn content in Se-Zn system. Dielectric dispersion is observed when Zn incorporated in Se-Zn glassy system. The results are explained on the basis of DC conduction mechanism and dipolar-type dielectric dispersion.

Electrical and dielectric properties of glass system NaPO 3–KHSO 4

Glass samples have been prepared in the NaPO 3–KHSO 4 binary system with the classical melting, casting and annealing steps. Electrical and dielectrical properties of glass samples were studied. Measurements of DC and AC conductivity and complex electrical permittivity of xNaPO 3–(100 − x)KHSO 4 glass system were carried out at temperatures ranging from room temperature to temperature located 15 °C below glass transition temperature T g. Results showed that changes of NaPO 3 concentration considerably affect values of observed parameters. DC conductivity of glass increases as NaPO 3 concentration grows until concentration x = 60. However, beyond this value a sharp decrease of DC conductivity was observed. In addition relaxation times showed abrupt changes at concentration x = 60, corresponding to the lowest relaxation times at the temperature 90 °C.

Study of DC conductivity and relative magnetic permeability of nanoparticle NiZnFe 2O 4/PPy composites

The DC conductivity and the relative magnetic permeability have been measured as functions of temperature for five powder samples of nanoparticle ferrites (Ni x Zn 1− x Fe 2O 4; x=0, 0.25, 0.5, 0.75 and 1), a pure polypyrrole (PPy) powder sample and many composite samples prepared by mixing different ratios of the ferrites to PPy. By comparing the results it is found that there is an obvious increase in DC conductivity of the ferrite/PPy composite samples compared to the corresponding pure ferrite samples, whereas compared to the pure PPy sample there is a decrease in DC conductivity. On the contrary, the magnetic permeability of the composites is higher than that of the pure PPy sample and lower than that of the pure ferrite samples as was expected.

Mixed polaronic-ionic conduction in lithium borate glasses and glass-ceramics containing copper oxide

The effect of electric field strength on conduction in lithium borate glasses doped with CuO with different concentration was studied and the value of the jump distance of charge carrier was calculated. The conductivity measurements indicate that the conduction is due to non-adiabatic hopping of polarons and the activation energies are found to be temperature and concentration dependent. Lithium borate glasses are subjected to carefully-programmed thermal treatments which cause the nucleation and growth of crystalline phases. X-ray diffraction analysis confirmed the amorphous nature for the investigated glass sample and the formation of crystalline phase for annealed samples at 650 °C. The main separated crystalline phase is Li2B8O13. The scanning electron micrographs of some selected glasses showed a significant change in the morphology of the films investigated due to heat treatment of the glass samples. It was found that the dc-conductivity decreases with an increase of the HT temperature. The decrease of dc conductivity, with an increase of the HT temperature, can be related to the decrease in the number of free ions in the glass matrix. There is deviation from linearity at high temperature regions in the logσ-1/T plots for all investigated doped samples at a certain temperature at which the transition from polaronic to ionic conduction occurs. The hopping of small polarons is dominant at low temperatures, whereas the hopping of Li+ ions dominates at high temperatures.

Dielectric behavior and impedance spectroscopy of bismuth iron phosphate glasses

The electrical and dielectrical properties of Bi2O3–Fe2O3–P2O5 glasses were measured by impedance spectroscopy in the frequency range from 0.01Hz to 4MHz and over the temperature range from 303 to 473K. It was shown that the dc conductivity strongly depends on the Fe2O3 content and Fe(II)/Fetot ratio. With increasing Fe(II) ion content from 17% to 34% in the bismuth-free 39.4Fe2O3–59.6P2O5 and 9.8Bi2O3–31.7Fe2O3–58.5P2O5 glasses, the dc conductivity increases. On the other hand, the decrease in dc conductivity for the glasses with 18.9mol% Bi2O3 is attributed to the decrease in Fe2O3 content from 31.7 to 23.5mol%, which indicates that the conductivity for these glasses depends on Fe2O3 content. The conductivity for these glasses is independent of the Bi2O3 content and arises mainly from polaron hopping between Fe(II) and Fe(III) ions suggesting an electronic conduction. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency the dispersion was investigated in terms of dielectric loss. The thermal activated relaxation mechanism dominates the observed relaxation behavior. The relationship between relaxation parameters and electrical conductivity indicates the electronic conductivity controlled by polaron hopping between iron ions. The Raman spectra show that the addition of up to 18.9mol% of Bi2O3 does not produce any changes in the glass structure which consists predominantly of pyrophosphate units.

Solution grown Pb 1− xCo xS semiconductor nanoparticle films

Pb 1− x Co x S ternary alloy films were grown using solution growth technique. X-ray fluorescence spectroscopy was used for compositional analysis. X-ray diffraction and atomic force microscopy analysis indicate the presence of nanometer-size grains in the films. Size dependence of optical band gap ( E g) is observed in the ternary nanoparticle films. Increase in E g and decrease in DC-conductivity with increase in Co concentration is also observed.

Effect of Bi 2O 3 on EPR, optical transmission and DC conductivity of vanadyl doped alkali bismuth borate glasses

Glasses with composition xBi 2O 3·(30− x)M 2O·70B 2O 3 (M=Li, Na) containing 2 mol% V 2O 5 have been prepared over the range 0≤ x≤15 ( x is in mol%). The electron paramagnetic resonance spectra of VO 2+ of these glasses have been recorded in the X-band (≈9.3 GHz) at room temperature (RT≈300 K). Spin Hamiltonian parameters, g ∥, g ⊥, A ∥, A ⊥, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. The molecular orbital coefficients, α 2 and γ 2, have been calculated by recording the optical transmission spectra. In xBi 2O 3·(30− x)Li 2O·70B 2O 3 glasses there is decrease in the tetragonality of the V 4+O 6 complex for x up to 6 mol% whereas for x≥6 mol%, tetragonality increases. In xBi 2O 3·(30− x)Na 2O·70B 2O 3 glasses there is increase in the tetragonality of the V 4+O 6 complex with increasing x. The 3d xy orbit expands with increase in Bi 2O 3:M 2O ratio. Values of the theoretical optical basicity, Λ th, have also been reported. The DC conductivity increases with increase in temperature. The order of conductivity is 10 −5 ohm −1 m −1 at low temperature and 10 −3 ohm −1 m −1 at high temperature. The DC conductivity decreases and the activation energy increases with increase in Bi 2O 3:M 2O ratio.

Ionic conductivity and the mixed alkali effect inLixRb1−xPO3glasses

The temperature and frequency dependent ionic conductivity in ${\mathrm{Li}}_{x}{\mathrm{Rb}}_{1\ensuremath{-}x}{\mathrm{PO}}_{3}$ glasses has been studied using dielectric spectroscopy. The dc conductivity decreases by more than six orders of magnitude on mixing the alkali ions in the glass structure, that is, a strong mixed alkali effect on the dc conductivity was observed. The results show that the mixed alkali effect on the dc conductivity diminishes as the temperature is increased. An ac conductivity mixed alkali effect can be observed up to high frequencies, although it gradually becomes weaker as the frequency is increased. A quantitative analysis of the conductivity spectra shows that the number of mobile cations in the single alkali glasses is, within experimental uncertainty, temperature independent. The results are discussed in relation to a detailed microscopic structural model taking into account the random mixing of alkali ions [Phys. Rev. B 63, 132202 (2001)].

Percolation-Limited Ionic Diffusion in Li0.5-xNaxLa0.5TiO3 Perovskites (0 ≤ x ≤ 0.5)

The dependence of ionic transport properties on the structure and composition of perovskites Li0.5-xNaxLa0.5TiO3 (0 ≤ x ≤ 0.5) has been analyzed by means of ND, XRD, NMR, and impedance spectroscopy. Local lithium mobility is shown to decrease progressively by 2 orders of magnitude along the series; however, long-range dc conductivity decreases sharply at x = 0.2 more than 6 orders of magnitude. The decrease of dc conductivity from values typical of fast ionic conductors, 10-3 S/cm at room temperature, to values of insulators, 10-10 S/cm, is discussed in terms of a three-dimensional percolation model for lithium diffusion. As deduced from XRD and ND data, the number of vacant sites in conduction pathways is controlled by the amount of Na and La in the perovskite.

Electrical properties of sodium phosphate glasses containing Al 2O 3 and/or Fe 2O 3. Part II

The electrical properties for three series of glasses: xNa 2O–(40− x)Al 2O 3–60P 2O 5, (20⩽ x⩽35), (NAP); 20Na 2O– xAl 2O 3–(20− x)Fe 2O 3–60P 2O 5, (5⩽ x⩽15), (NAFP), and xNa 2O–(40− x)Fe 2O 3–60P 2O 5, (20⩽ x⩽35), (NFP) glasses were measured by impedance spectroscopy in the frequency range from 1 Hz to 1 MHz and over the temperature range from 303 to 473 K. It was shown (in Part I) that the addition of Fe 2O 3 has significant effects on the structure of these glasses and Fe ions play a different structural role in phosphate network than that of Al ions. Such effects reflect changes in the origin of electrical conduction. With increasing Fe 2O 3 content in NAFP and NFP glasses the dc conductivity depends upon distance between iron ions and the activation energy of 53.1 kJ mol −1 indicates electronic conduction. On the other hand, the decrease in dc conductivity and activation energy for glasses in NAP series is attributed to the decrease in Na 2O content from 35 to 20 mol%. The activation energy varies from 80.1 to 72.4 kJ mol −1 for NAP glasses suggesting ionic conduction. The impedance analysis for these glasses shows that the changes in the electrical conduction mechanisms coincide with the changes in the structure.