Dielectric relaxation and ion transport in silver–boro-tellurite glasses

Glass systems of composition xAg₂SO₄–20Ag₂O–(80?x) [0.50 B₂O₃–0.50 TeO₂], where x = 5, 10, 15, 20, 25 and 30 mol% have been prepared by melt-quenching technique. Frequency- and temperature-dependent conductivity measurements have been carried out in the frequency range 10 Hz to 10 MHz and at a temperature range of 303–353 K, respectively. DC conductivities exhibit Arrhenius behavior over the entire temperature range with a single activation barrier. Addition of Ag₂SO₄ expands the glass network and, consequently, conductivity increases. This suggests that the structure and network expansion are the key parameters for enhancing conductivity. Impedance spectra of these glasses show a single semicircle, indicating one type of conduction. AC conductivity behavior of the glasses was analyzed using both single power law and Kolhrauh–William–Watts (KWW) stretched exponential relaxation function. The power law exponent (s) is temperature-dependent, while the stretched exponent (β) is insensitive to temperature. Scaling behavior has also been carried out using reduced plots of conductivity with frequency, which suggests the ion transport mechanism remains unaffected by temperature and composition.     

Dielectric behavior of sodium borate glasses

The dielectric constant and the electrical conductivity of the transparent glasses in the composition 3Na₂O-7B₂O₃ (NBO) were investigated in the 100 Hz–10 MHz frequency range at various temperatures. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 0.76 ± 0.02 eV, close to that (0.74 ± 0.02 eV) obtained from DC conductivity studies. The frequency-dependent electrical conductivity was analyzed using Jonscher’s power law. Temperature-dependent behavior of the frequency exponent (n) suggested that the correlated-barrier hopping model was the most appropriate to rationalize the electrical transport phenomenon in NBO glasses.     

On the power-law behavior of the AC conductivity of the mixed crystal (NH4)3H(SO4)1.42(SeO4)0.58

A power law used to describe the AC conductivity from 299 to 393 K of the mixed crystal (NH₄)₃H(SO₄)_1.42(SeO₄)_0.58 led to fractional exponent values ranging from 1.08 to 0.91, depending on structural changes induced on temperature variation [B. Louati, M. Gargouri, K. Guidara and T. Mhiri, J. Phys. Chem. Solids 66 (2005) 762]. In the present note, we suggest that the fractional law exhibits features of lattice relaxation. Despite the structural changes, the parameters of the power law are mutually interconnected to yield a temperature independent phenomenon. Such behavior is probably of general validity and characterizes the universal fractional dispersion of the AC conductivity, as it was also observed in glasses of different composition.     

Transport properties of hexanoyl chitosan-based gel electrolyte

Films of hexanoyl chitosan-based polymer electrolyte were prepared by the technique of solution casting. The effect of plasticizer on the transport properties of hexanoyl chitosan:lithium trifluoromethanesulfonate (LiCF₃SO₃) electrolytes have been investigated. The plasticizer used was ethylene carbonate (EC). The highest room temperature conductivity achieved in the EC-plasticized hexanoyl chitosan-based electrolytes is 2.75×10⁻⁵ S cm⁻¹. The Rice and Roth model was used to explain the variations in the dc conductivity observed. The exponent, s, in Jonscher’s universal power law equation σ(ω)=σ _dc+Aω ^s , was analyzed as a function of temperature for the sample containing 30 wt% of EC. The analysis suggests that the conduction mechanism follows that proposed by the overlapping large polaron tunneling model.     

Investigation of the Ag2SO4 — BaSO4 binary system from an SOx sensor point of view

The binary phase diagram of Ag₂SO₄ — BaSO₄ system is proposed using X-ray powder diffraction, thermal analysis (DTA/DSC), scanning electron microscopy, and electrical conductivity results. About 5 mol-% BaSO₄ is soluble in β-Ag₂SO₄. The two-phase (Ag₂SO₄+BaSO₄) mixture exists for 10–90 mol-% of BaSO₄ between room temperature and 578 °C. An eutectic of 578 °C exists of the composition 70Ag₂SO₄+30BaSO₄ The conductivity maximum within the solid solubility limits is due to the generation of extrinsic vacancies and lattice expansion as a result of partial substitution of the bigger aliovalent Ba²⁺ for the Ag⁺-ions. The eutectic composition shows the maximum conductivity in the entire binary system due to the minimum in grain size, thereby providing a maximum surface ion conducting path. About 1 min response time of the sensor based on using the eutectic composition, as solid electrolyte, is much shorter than that of the sensor with pure Ag₂SO₄.     

Dielectric behaviour and AC conductivity of LiCF3SO3 doped H-chitosan polymer films

H-chitosan that exhibited solubility in THF was prepared by acyl modification of chitosan. Films of H-chitosan containing LiCF₃SO₃ were prepared by the solution cast technique. The effect of salt concentration on the frequency-dependent dielectric properties of H-chitosan: LiCF₃SO₃ complexes were investigated by impedance spectroscopy, in the temperature range from 243 to 373 K. The dielectric properties and ac conductivity of the samples prepared have been analyzed. The dielectric constant increases sharply with temperature in the low frequency region. At higher frequencies, the effect of temperature on the dielectric constant is negligible. The values of dielectric constant were also found to increase with increasing conductivity of the samples. The imaginary part, M_i of electrical modulus shows the formation of dispersion peak. Relaxation times for the ionic charge carriers were extracted from the loss tangent maximum peak at various temperatures. The plot of relaxation times as a function of temperature shows Arrhenius type behaviour. The ac conductivity was found to obey the universal power law and as the temperature increases, the feature of σ(θ) α θⁿ is more predominant. The temperature dependence of the power law exponent n is reasonably interpreted by the overlapping large polaron tunneling (OLPT) model.     

Electrical conductivity of binary sulphates of lithium sulphate

To engineer lithium sulphate based material with high ionic conductivity at lowest possible temperature, the electrical conductivity of binary sulphates of Li₂SO₄ with Na₂SO₄, K₂SO₄, MgSO₄, ZnSO₄ and Ag₂SO₄ has been measured in the temperature range from 513 K to 773 K. The results are interpreted on the basis of different phases present therein. Li₂SO₄:Ag₂SO₄(40:60) mol % has high ionic conductivity = 2.17×10^-3(ohm cm)^-1 at 606 K which could be utilized in power sources.     

Dielectric properties and conductivity in CuO and MoO3 doped borophosphate glasses

A novel set of glasses of the type (B₂O₃)_0.10-(P₂O₅)_0.40-(CuO)_0.50−x-(MoO₃)_x, 0.05≤x≥0.50, have been investigated for dielectric properties in the frequency range 100 Hz-100 kHz and temperature range 300-575 K. From the total conductivity derived from the dielectric spectrum the frequency exponent, s, and dc and ac components of the conductivity were determined. The temperature dependence of dc and ac conductivities at different frequencies was analyzed using Mott's small polaron hopping model, and the high temperature activation energies have been estimated and discussed. The observed initial decrease in conductivity (ac and dc) and increase in activation energy with the addition of MoO₃ have been understood to be due to the hindrance offered by the Mo⁺ ions to the electronic motions. The observed peak-like behavior in conductivity (dip-like behavior in activation energy) in the composition range 0.20-0.50 mol fractions of MoO₃ may be due to mixed transition effect occurring in the present glasses. The temperature dependence of frequency exponent, s, has been analyzed using different theoretical models. It is for the first time that the mixed transition metal ion (TMI) doped borophosphate glasses have been investigated for dielectric properties and conductivity over wide temperature and frequency ranges and the data have been subjected to a thorough analysis.     

Effective exponents for de almeida-thouless line

The experimental irreversibility line at the magnetic phase diagram H-T of spin glasses is often approximated using a power law Hα (T_G-T)^φ/2. The mean field theory of de Almeida and Thouless predicts φ=3 for temperatures T close to the spin-glass transition temperature T_G . For a range of reduced temperature involved in an experiment one should use, however, effective exponents (φ>3) obtained by fitting the power law to the exact expression for de Almeida-Thouless line. These compare favorably with experimental values of φ obtained for different spin glasses. The increase of effective exponent up to φ=7 on approaching the spin-glass-ferromagnetism multicritical point is also considered.     

Structural and electrical investigation of (Ag3AsS3)x(As2S3)1?x superionic glasses

Structural studies of (Ag₃AsS₃) _x (As₂S₃)_1−x chalcogenide superionic glasses in the compositional range x = 0.3–0.9 were performed by scanning electron microscopy. Temperature and compositional dependences of transmission coefficient, electrical conductivity, and activation energy were investigated     

Electrical properties of Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-based composite systems

Composite electrolytes are well-known multiphase systems and exhibit maxima in the conductivity at certain second-phase concentration. An attempt has been made to investigate a number of sodium sulfate (Na₂SO₄)-based composite systems. The dispersoids that have been used are MgO, Al₂O₃, and SiO₂. The samples have been characterized using impedance spectroscopy, X-ray diffraction, and differential scanning calorimetry. The maximum conductivity has been observed for MgO dispersed system, and the percolation threshold has been observed at 30-mol% dispersoid, MgO concentration. Interestingly, two maxima have been observed in case of the Na₂SO₄–SiO₂ and Na₂SO₄–Al₂O₃ composite systems. In the Na₂SO₄–SiO₂ system, the first maximum occurs at lower concentration, i.e., in the range between 10 and 20 mol%, whereas the second occurs at the 40-mol% dispersoid concentration. For the Na₂SO₄–Al₂O₃ system, although slightly indistinguishable, two peaks in the conductivity vs composition plot have been observed around 12- and 30-mol% Al₂O₃ concentrations.     

Ion transport studies in zinc/cadmium halide doped silver phosphate glasses

A number of samples of silver phosphate glasses Ag₂O−P₂O₅−Zn/CdX₂ (X=Cl, Br or I) with 1, 5, 10 and 20 mol-% zinc or cadmium halides have been prepared. Control samples of undoped silver phosphate glasses were also prepared. These glasses were characterized by elemental analysis, X-ray diffraction, IR spectra, differential scanning calorimetry, transference number measurements and electrical conductivity studies. These glasses were found to be essentially ionic conductors. The undoped silver phosphate glass (Ag₂O−P₂O₅) has a low σ value in comparison to the doped ones. The conductivity (σ) in the doped glasses increases substantially with increasing concentration of dopant salts Zn/or CdX₂ and as the anions of the dopants are changed from Cl⁻ to I⁻. It is found that the σ values of the ZnX₂ doped glasses are slightly greater than those of the CdX₂ doped ones, and the silver phosphate glasses doped with (20 mol-%) Zn/CdI₂ yielded maximum conductivity. The results have been discussed and explained on the basis of changes in the structure of the glass matrix by the addition of dopant ions of different sizes, IR spectra and thermal studies.     

Frequency dependent magnetoconductivity and conductivity study in Ni-dispersed silica nano-composite produced by sol-gel technique

The low frequency (20 Hz to 1 MHz) ac conductivity and magnetoconductivity behaviour of ceramic nanocomposite (Ni-SiO₂) at low temperature down to 77 K are reported. The frequency dependent conductivity followed the power law, σ(ω) ∝ ω ^s . The fractional exponent s is a function of temperature and was found to increase with increasing temperature. This type of variation may be attributed to small polaron hopping. A peak present in the loss tangent indicates the presence of a Debye relaxation process. The magnetoconductivity of the samples is positive, which strongly depends on frequency. A firm theoretical explanation of frequency dependent magnetoconductivity is still lacking.     

Sol–gel synthesis,structural and ion transport studies of lithium borosilicate glasses

Lithium borosilicate (LBS) glasses of different modifier to formers (m/f) ratios were synthesized through sol–gel process. Structural characterisation of LBS glasses were made using XRD, FTIR and DSC techniques. XRD pattern of LBS samples showed amorphous phase for gels heat treated between 573 and 698 K and further heat treatment above 698 K showed the formation of crystalline multiphases. FTIR spectra for dried LBS gels between 338 and 443 K showed the presence of hydroxyl group on the surface of silicate and borates matrix and on heat treatment, the FTIR spectra revealed the formation of silicate and borate linkages in LBS glassy matrix. DSC curve confirmed the presence of adsorbed water molecules in LBS glassy matrix. Impedance measurements were carried out on LBS samples of different m/f ratios as a function of temperature and data were analyzed using Boukamp equivalent circuit software. The conductivity of LBS glasses at different temperatures was calculated from analyzed impedance data. Activation energy (E_a) is obtained from Arrhenius plots of the dc conductivity and it is found to be 0.64 (±0.02) eV for high conducting sample. ac conductivity is calculated from impedance data and analyzed using Jonscher's power law (JPL) exponent (s) for m/f ratios of LBS samples at different temperatures. The power law exponent s of LBS glasses exhibited a non-linear behavior with temperature. The electric modulus data were fitted with Kohlraush–William–Watts (KWW) stretched exponential function and the modulus formalism is used to study the ionic relaxation behavior in LBS samples.     

Elastic properties of TeO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Ag<Subscript>2</Subscript>O glasses

A series of glasses [(TeO₂) _x (B₂O₃)_1−x ]_1−y [Ag₂O] _y with x = 70 and y = 10, 15, 20, 25 and 30 mol% were synthesised by rapid quenching. Longitudinal and shear ultrasonic velocity were measured at room temperature and at 5 MHz frequency. Elastic properties, Poisson's ratio, microhardness, softening temperature and Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental results indicate that the elastic constants depend upon the composition of the glasses and the role of the Ag₂O inside the glass network is discussed. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Comparison between the experimental elastic moduli data obtained in the study and the calculated theoretically by the mentioned above models has been discussed.     

AC Conductivity,XRD and transport properties of melt quenched PbI<Subscript>2</Subscript>–Ag<Subscript>2</Subscript>O–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Composite materials used for electrode and electrolyte materials have been intensely studied in view of their advantages such as higher conductivity and better operational performance compared to their single-phase counterparts. The present work aims at studying the electrical and structural characteristics of a new composite electrolyte namely, (PbI₂) _x  − (Ag₂O–Cr₂O₃)_100−x where x = 5, 10, 15, 20, and 25 mol%, respectively, prepared by the melt quenching technique. The room temperature X-ray diffraction spectra revealed certain crystalline phases in the samples. AC conductivity analysis for all the prepared samples was carried out over the frequency range 1 MHz–20 Hz and in the temperature window 297–468 K. The room temperature conductivity values were calculated to be in the order of 10⁻⁵–10⁻³ Scm⁻¹. An Arrhenius dependence of temperature with conductivity was observed, and the activation energies calculated were found to be in the range 0.27–0.31 eV. Furthermore, the total ionic transport number (t _i) values obtained for all these indicated the ionic nature of this system. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Effect of ionizing radiation on the dielectric characteristics of TlInSe<Subscript>2</Subscript> and TlGaTe<Subscript>2</Subscript> single crystals

The temperature dependences of the electrical conductivity and the permittivity of TlInSe₂ and TlGaTe₂ crystals unirradiated and irradiated with 4-MeV electrons at a doze of 10¹⁶ cm⁻² have been investigated. It has been established that electron irradiation leads to a decrease in the electrical conductivity σ and the permittivity ɛ over the entire temperature range under study (90–320 K). It has been revealed that the TlInSe₂ and TlGaTe₂ single crystals undergo a sequence of phase transitions characteristic of crystals of this type, which manifest themselves as anomalies in the temperature dependences σ = f(T) and ɛ = f(T). Electron irradiation at a doze of 10¹⁶ cm⁻² does not affect the phase transition temperatures of the crystals under investigation.     

Pecularities of change transfer mechanism and dielectric properties of glasses Ag-Sb-S-I

Temperature dependence of electronic and ionic components of electric conductivity and dielectric permittivity of amorphic compounds Ag_0.25Sb_0.25S_0.5, (AgSbS₂)_0.95· (SbSI)_0.05 and (AgSbS₂)_0.9·(SbSI)_0.1 in the temperature range of 290–380 K have been investigated. The experimental data show that glasses investigated are solid electrolytes. Ionic conductivity as well as dielectric permittivity of the glasses Ag-Sb-S may be changed by introduction of SbSI.     

Preparation of sol-gel method P2O5-Al2O3-SiO2 glasses and their characterization

Nanostructures P₂O₅-Al₂O₃-SiO₂ glasses were prepared by sol-gel method. The glasses were characterized by XRD, FTIR and TG/DTA methods. The average pore size of the glass was less than 3 nm as measured by N₂ adsorption — desorption method. The thermal stability was measured as a function of decomposition temperature and weight loss calculations. Proton conductivities of all samples increased with an increase in relative humidity (40–90 %), indicating that continuous paths suitable for proton conduction were developed when glasses heat treated at 300 °C due to the adsorption of water. The temperature dependence of the conductivity for all compositions increases with increasing temperature in the range 30–90 °C with relative humidity 70 %. The overall conductivity was in the range 10⁻⁴–10⁻³ S/cm for compositions.     

Survey of the pre-factor of the power-law frequency dependence in the silver conducting chalcogenide glasses

The variation of parameter A in the power-law conductivity dependence on the frequency,() = A ^s, for chalcogenide glasses (Ag₂S)_x(GeS₂)_1-x, where 0相似文献