Preparation and thermal properties of novel Li2S-Sb2S3 glassy system

There is great interest in sulfide glasses because of their high lithium ion conductivity. A new Li₂S-Sb₂S₃ glassy system has been prepared by a classical quenching technique. Thermal characterization has been carried out and it has been observed that the T_g decreases with an increase in the concentration of Li₂S. However, this tendency stops around 17% Li₂S content. Results have been discussed on the basis of the modification that would occur in the base Sb₂S₃ glass network by the addition of Li₂S.     

Electrochemical characterizations and the effect of glycerol in biopolymer electrolytes based on methylcellulose-potato starch blend

ABSTRACT

Polymer electrolytes have been prepared by blending methylcellulose (MC)-potato starch, doped with lithium perchlorate (LiClO₄) and plasticized with glycerol. The blend of 60 wt% MC-40 wt% starch was found to be the most suitable ratio to serve as polymer host. Fourier transform infrared (FTIR) spectroscopy analysis proved the interaction among the components. X-ray diffraction (XRD) analysis indicated that the conductivity enhancement is due to the increase in amorphous content. The highest ionic conductivity obtained at room temperature was (4.25 ± 0.82) × 10^?4 S cm^?1 for MC-starch-LiClO₄-20 wt% glycerol. The highest conducting samples in both systems were found to obey Arrhenius rule. Dielectric study further strengthens the conductivity result.     

Ionic conductivity of Li2O-BaO-Bi2O3 glasses

Dc and ac conductivities of Li₂O-BaO-Bi₂O₃ glasses have been studied in a temperature range of 263-523 K and a frequency range of 10 Hz-2 MHz and have been compared with those of binary Li₂O-Bi₂O₃ glasses. The frequency dependent conductivity has been studied employing both the modulus and conductivity formalisms. We have observed small changes in the dc conductivity and its activation energy from those of the binary glass when content of BaO is small. However we have observed noticeable changes in the conductivity and the activation energy when BaO content is large. The significant changes in the values of the non-exponential parameter and the power-law exponent of the ac electrical properties have been observed due to introduction of BaO in the lithium bismuthate glasses. The existing relation between the power-law exponent and the non-exponential parameter was also violated in the present glass compositions.     

DC conduvtivity of V2O5TeO2 glasses

The dc conductivity of semiconducting vanadium tellurite glasses of compositions in the range 50 to 80 mol% V₂O₅ has been measured in the temperature region 77 to 400 K. Measurements have been made on annealed samples at different annealing temperatures. Annealing the samples at temperature of about 250°C causes the appearance of a complex crystalline phase resulting in an increase of conductivity. Results are reported for amorphous samples of different compositions. The conductivity of tellurite glasses is slightly higher than the corresponding composition of phosphate glasses, but the general trend of the increase of conductivity and decrease of high temperature activation energy with increasing V₂O₅ content is similar in the two systems. The data have been analysed in the light of existing models of polaronic hopping conduction. A definite conclusion about the mechanics of conduction (adiabatic or nonadiabatic) is difficult in the absence of a precise knowledge of the characteristic phonon frequency v₀. Adiabatic hopping is indicated for v₀～10¹¹ Hz, however this value leads to unreasonably low value for the Debye temperature θ_D, and higher values for v₀～10¹³ hz satifiies the conditions for nonadiabatic hopping which appears to be the likely mechanism of conduction in V₂O₅TeO₂ glasses. The low temperature data (< 100 K) can be fitted to Mott's variable range hopping, which when combined with ac conductivity data gives reasonable values of α, but a high value for the disorder energy.     

Growth and ionic conductivity of Li3 + x P1 − x GexO4 (x = 0.34) single crystals

Li_{3 + x} P_{1 ? x} Ge_xO₄ crystals (x = 0.34) with dimensions of about 3 × 3 × 5 mm³ were grown for the first time from flux. The conductivities of the crystals measured along three directions have close values and are equal to σ ≈ 1.8 × 10^?6 and 3.7 × 10^?2 Sm/cm at the temperatures 40 and 400°C, respectively (similar to the case of pure lithium phosphate, somewhat lower values of electric conductivity were measure along the b axis). The activation energy of conductivity is equal to 0.54 eV. A considerable increase in the conductivity of the solid solution in comparison with the conductivity of pure lithium phosphate is explained by the specific features of the lithium sublattice in the crystal structure of the λ-Li₃PO₄ type.     

Electronic transport properties of mixed transition metal ions doped borophosphate glasses

A series of borophosphate glasses in the composition (B₂O₃)_0.10–(P₂O₅)_0.40–(CuO)_0.50?x–(MoO₃)_x; 0.05 ? x ? 0.50 have been investigated for room temperature density and dc conductivity over the temperature range from 350 to 650 K. The density decreased with increase in MoO₃ over the composition range studied except a slight increase around 0.35 mole fraction. The observed initial decrease in conductivity with the addition of MoO₃ has been attributed to the hindrance offered by the Mo⁺ ions to the electronic motions. The observed peak-like behavior in conductivity in the composition range 0.20 – 0.50 mol% of MoO₃ is ascribed to the mixed transition metal ion effect (MTE). Mott’s small polaron hopping model has been used to analyze the high temperature conductivity data and the activation energy for conduction has been determined. The low temperature conductivity has been analyzed in view of Mott’s and Greaves variable range hopping models. It is for the first time that conduction mechanisms have been explored and MTE detected in mixed transition metal ions doped borophosphate glasses.     

Electronic conductivity and structural chemistry in Li-Te-V oxide glasses

The electronic conductivity of the Li₂O-Te₂V₂O₉ glass system reveals that, even for high lithium content, electron hopping occurs between V⁴⁺ and V⁵⁺. The study of the V⁴⁺ content versus various syntheses shows that more than lithium content, the nature of the counter ion used in Li⁺ reagent and its decomposition behavior are responsible for the efficiency of the spontaneous V⁵⁺ reduction via a ‘sprouting’ phenomenon. The electron hopping process implies interconnection of VO_n polyhedra which are accessible for both V⁴⁺ and V⁵⁺ species. Such fact gives information about short and medium range ordering in the glasses. On the basis of the LiVTeO₅ crystal structure and in agreement with wide angle X-ray scattering experiments, a possible rearrangement bringing together VO₅ square pyramids is proposed to explain the electron hopping. Such proposal corresponds to a lithium network forming effect. It could explain why for Li/V>1 the electronic conductivity increases with lithium content while the V⁴⁺ amount remains low.     

Mixed conductivity in tungstenite–phosphate glasses containing alkali metal ions

The conductivity of glasses in the 50WO₃–(50 ? x)P₂O₅–xA₂O (A = Na, K, Cs) system has been investigated as a function of composition. It is shown that in tungstenite–phosphate glasses containing different alkali metal ions the conductivity decreases with an increase in the alkali metal ion content. A decrease in conductivity is larger for heavier ions and reaches more than seven orders of magnitude in the case of glass containing Cs₂O. This behavior remains in contrast to the literature data on conductivity in transition metal oxide glasses containing alkali metal ions where usually strong conductivity anomalies of several orders of magnitude at certain amount of ions are observed. No necessity of ion–polaron interaction has been pointed out.     

Diaquobis-μ-(dimethylsulfoxo)bis(dimethylsulfoxo) dilithium tetraphenylborate

The structure of diaquobis--(dimethylsulfoxo)bis(dimethylsulfoxo)dilithium tetraphenyl- borate, [Li₂(Me₂SO)₄(H₂O)₂][BPh₄]₂, has been determined at 293 K. The compound crystallizes in the triclinic P-1 space group (a = 11.429(2) Å, b = 14.068(3) Å, c = 19.215(4) Å, = 69.31(3), = 88.98(3), = 89.03(3)). The lithium is coordinated to the oxygens of an aquo ligand, a terminal dimethylsulfoxo ligand, and two bridging dimethylsulfoxo ligands. The coordination geometry of each lithium is significantly distorted from a tetrahedron by the twisting of the plane containing the lithium ion and the two bridging dimethylsulfoxo oxygens relative to the plane containing the lithium ion and the terminal dimethylsulfoxo and aquo oxygen atoms. Hydrogen bonding between the aquo hydrogens and the phenyls of the tetraphenylborate anion is observed but does not result in a polymeric structure as has been observed in other lithium tetraphenylborate salts because of the 1:1 ratio of aquo ligands and tetraphenylborate anions.     

Pyroelectric Properties of Potassium and Rubidium Titanyl—Arsenate Single Crystals in the Temperature Range of 4.2–300 K

The temperature dependences of the pyroelectric coefficients of KTiOAsO₄ and RbTiOAsO₄ single crystals grown by flux crystallization have been investigated in the temperature range of 4.2–300 K. With an increase in temperature, superionic conductivity first arises in KTiOAsO4 (at T > 200 K) and then (at T > 270 K) in RbTiOAsO₄. This conductivity is much higher in the samples polarized at T = 4.2 K. An exponential change in the crystal resistivity along the polar direction is simultaneously observed. The results of measurements in the range of 4.2–200 K indicate larger values of pyroelectric coefficients when compared with potassium and rubidium titanyl-phosphate crystals. A correlation between the pyroelectric coefficients and a change in the lattice constants at isomorphic substitutions of K atoms for Rb and P atoms for As has been revealed within the symmetry approach.     

Dependence of Electrical Conductivity (σ) and Activation Energy of Lithium Ferrite on Sintering Temperature and Porosity

The electrical conductivity (σ) of lithium ferrite sintered at 950, 1000, 1050 and 1100 °C was investigated in the temperature range of 300 to 1000 K. Three distinct regions have been observed in log (σT) vs 10³/T curves for four samples of lithium ferrite sintered at different temperatures. The conduction in the first region is due to impurities. In the second and third region is due to ordered and disordered state of the material. The transition from the first region to the second region is due to lowering of symmetry. The transition from second to third region is due to magnetic transition, i.e. ferrimagnetic to paramagnetic state. The transition temperatures are nearly equal to the Curie temperatures of the materials. The porosity and activation energy were calculated. It was found that the electrical conductivity is progressively increasing with increase of sintering temperature while the porosity and activation energy decrease continuously. The Seebeck coefficient (Q), carrier concentration (n) and mobility (μ) of charge carriers have been discussed as a function of sintering temperature and temperature.     

Electrical Conductivity of Tetrathiafulvalene-9-Dicyanomethylene-2,4,5,7-tetranitrofluorene(TTF-DT4-NF)

We deal with optical properties of TTF-DT₄NF together with electrical conductivity measurements made with rod-like samples carrying a silver paint contact at both ends. Schottky barrier formation was observed in each case, although strongly modified by tunneling carries across the only thin barriers formed due to a high impurity content of the samples. In the higher voltage range non-ohmic bulk conductivity behaviour is manifest.     

Pyroelectric properties of real LiNbO3 single crystals grown from a congruent melt

The temperature dependences of the pyroelectric coefficient of lithium niobate single crystals grown from a congruent melt have been investigated in the range of 4.2–300 K. No anomalies were found at low temperatures, and the experimental dependence is described well by the Debye-Einstein model, with T _D = 357 K and two pyroactive frequencies of 692 and 869 cm^?1. Specific features of lithium niobate have been analyzed. Two sublattices, formed by two pairs of mesotetrahedra with (according to the symmetry conditions) dipole and octupole moments, were selected in the structure. Their contributions to the total polarization differ by an order of magnitude. Vacuum annealing of the samples leads to the occurrence of anomalies only at temperatures over 280 K; these anomalities are interpreted as a manifestation of superionic conductivity.     

Effect of LiCF3SO3 on L-Chitosan/PMMA Blend Polymer Electrolytes

This paper focuses on the effect of lithium triflate (LiCF₃SO₃) on the structural and conduction properties of lauroyl (L)-chitosan/poly(metylmethacryalate) (PMMA)-based polymer electrolytes. Films of L-chitosan/PMMA blends and its complexes were prepared using a solution-casting technique. The ionic conductivity of the system was measured over a wide range of frequency between 50 Hz-1 MHz. Impedance plot for the samples demonstrates two well-defined regions. The disappearance of the high frequency semicircular region led to a conclusion that the current carriers are ions. Sample with 30 wt% of LiCF₃SO₃ showed the highest conductivity of 7.59 ± 3.64 × 10^?4 Scm^?1 at room temperature. This is consistent with the results obtained from infrared spectroscopy.     

Transport property measurements in tungsten sulphoselenide single crystals grown by a CVT technique

The transport properties of ternary mixed WS_xSe_2‐x single crystals have been studied by measuring the thermo power, electrical conductivities and Hall parameters in a small temperature range 303‐423 K. The electrical conductivity was highest for selenium rich WSe₂ and lowest for sulphur rich WS₂ crystals. All the crystals showed semiconducting behaviour from the temperature dependence of ‘ρ’, ‘R_H’ and ‘S’. The Hall coefficients showed that the samples are p‐type conducting. The temperature dependence of resistivity, Hall coefficients, carrier concentration showed that all of them are thermally activated. The values of activation energies, pre‐exponential factors and the scattering parameters have been determined. The dominant scattering mechanism for the charge carriers has been explained. The relation between the TEP and the concentration of charge carriers and electrical conductivity was studied. The effective masses of holes and the effective density of states have been determined. These parameters show an increase with increase in sulphur content. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and Electrical Properties of a Fluorite-Like Nd<Subscript>5</Subscript>Mo<Subscript>3</Subscript>O<Subscript>16</Subscript> Compound with Partial Substitution of Molybdenum by Tungsten,Niobium, or Vanadium

The phase formation of Nd₅Mo_{3 – x}W _x O_16.5, Nd₅Mo_{3 – x}Nb _x O_{16.5 – х/2}, and Nd₅Mo_{3 – x}V _x O_{16.5 – х/2} solid solutions based on a fluorite-like Nd₅Mo₃O_16.5 compound (mixed conductor with interstitial oxygen conductivity) has been studied. The electrical conductivity of doped compounds obeys the Arrhenius law and, at a low impurity content, is as high as 0.03–0.08 S/cm at 800°C. Substitution of Mo⁶⁺ cations by V⁵⁺ and Nb⁵⁺ cations reduces the interstitial oxygen content, which causes a decrease in the solid-solution electrical conductivity by 1–2 orders of magnitude and a decrease in the cubic unit-cell parameter. A wide diffuse anomaly with a maximum of about 1500–4000 has been observed in the temperature dependence of the permittivity for all single-crystal and polycrystalline samples in the range of 300–900°C.     

Electrical Conductivity and Thermoelectric Power of Silver Iododichromate Fast Ion Conducting Electrolytes

Fast ion conducting solid electrolytes are becoming increasingly important owing to their application in solid state ionic devices. The present work deals with the silver ion conducting x AgI – (1–x)Ag₂Cr₂O₇ electrolyte system. These electrolytes have been characterised by X-ray diffraction, electrical conductivity, electronic conductivity and thermoelectric power techniques. A high ionic conductivity of the order of 10⁻³ S/cm has been observed for the composition mol% 80 AgI–20 Ag₂Cr₂O₇, at room temperature. The electronic conductivity of this electrolyte is three orders of magnitude lower than the ionic conductivity.     

Solid-state NMR and XANES studies of lithium and silver silicate gels synthesized by the sol-gel route

The objective of this study is to understand the effect of low temperature sol-gel synthesis on the microstructural properties of lithium [xLi₂O-(1−x)SiO₂; x=0.1-0.8 in steps of 0.1] and silver [xAg₂O-(1−x)SiO₂; x=0.1-0.8 in steps of 0.1] silicate xerogels via solid state nuclear magnetic resonance (NMR) and X-ray absorption near edge structure (XANES) techniques. The Li silicate xerogels were analyzed with solid-state ⁷Li and ²⁹Si NMR and the Ag silicate xerogels were studied with Ag XANES. At high Li loading, ⁷Li NMR shows quadrupolar satellite transitions attributed to LiNO₃, a phase also found with X-ray diffraction (XRD). At low Li loading, both NMR and XRD results show an amorphous xerogel. The silicate network is monitored with ²⁹Si NMR and shows evidence of Li incorporation. For the Ag silicate xerogels, Ag-L-III XANES spectral studies show a local environment similar to AgNO₃ for low Ag loading levels, and an increased Ag oxidation for higher Ag loading levels. Si K edge spectra show only an amorphous phase, with no evidence of a crystalline quartz phase. The electrical conductivity of the lithium silicates was estimated from impedance data and the highest conductivity is exhibited by the 0.3Li₂O-0.7SiO₂ composition xerogel. The conductivity dependence on loading level strongly suggests that the observed conductivity is due to Li⁺ mobility. However, further experimental studies are needed to rule out the possibility that the conductivity is, at least in part, due to H⁺ mobility. Variation in conductivity is explained qualitatively using existing theoretical models.     

Electronic conductivity in zinc iron phosphate glasses

The electrical properties of (40−x)ZnO–xFe₂O₃–60P₂O₅ (x = 10, 20, 30 mol%) glasses were measured by impedance spectroscopy in the frequency from 0.01 Hz to 4 MHz and the temperature range from 303 to 473 K. It was shown that the dc conductivity strongly depends on the Fe₂O₃ content and Fe(II)/Fe_tot ratio. The increase in dc conductivity for these glasses is attributed to the increase in Fe₂O₃ content from 10 to 30 mol%. With increasing Fe(II) ion content from 6% to 17% the dc conductivity increases. This indicated that the conductivity arises mainly from polaron hopping between Fe(II) and Fe(III) ions suggesting an electron conduction in these glasses. By applying scaling on conductivity data measured at different temperatures, single master curve was obtained for each glass. On the other hand, deviation from the master curve at high frequencies was observed for glasses with different compositions. This deviation originates from a various mobility of charge carriers in different glass structures. Raman spectra showed the change of structure, from metaphosphate to pyrophosphate, with increasing Fe₂O₃ content from 10 to 30 mol%.     

Investigation of near constant loss contribution to conductivity in lithium bismo-silicate glasses

Glasses having compositions 20Li₂O · (80 − x)Bi₂O₃ · xSiO₂ (x = 55, 60, 65, 70 mol%) were investigated using impedance spectroscopy in the frequency range from 20 Hz to 1 MHz and in the temperature range from 543 to 663 K. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency are extracted from the impedance spectra. The increase in conductivity with increase in SiO₂ content is attributed to the change in the structural units of bismuth. Both electric modulus and the conductivity formalism have been employed to study the relaxation dynamics of charge carriers in these glasses. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of the dynamic processes for ions in these glasses. Similar values of activation energy for dc conduction and for conductivity relaxation time indicates that the ions overcome same energy barrier while conducting and relaxing. The observed conductivity spectra follows power law with exponent ‘s’ which increases regularly with frequency and approaches unity at higher frequencies. Near constant losses (NCL) characterize this linearly dependent region of conductivity spectra. A deviation from ‘super curve’ for various isotherms of conductivity spectra was also observed in high frequency region and at low temperatures, which supports the existence of different dynamic processes like NCL in addition to the ion hopping processes in the investigated glass system.