Solid polymeric electrolyte of PVC–ENR–LiClO<Subscript>4</Subscript>

The ionic conductivity of PVC–ENR–LiClO₄ (PVC, polyvinyl chloride; ENR, epoxidized natural rubber) as a function of LiClO₄ concentration, ENR concentration, temperature, and radiation dose of electron beam cross-linking has been studied. The electrolyte samples were prepared by solution casting technique. Their ionic conductivities were measured using the impedance spectroscopy technique. It was observed that the relationship between the concentration of salt, as well as temperature, and conductivity were linear. The electrolyte conductivity increases with ENR concentration. This relationship was discussed using the number of charge carrier theory. The conductivity–temperature behaviour of the electrolyte is Arrhenian. The conductivity also varies with the radiation dose of the electron beam cross-linking. The highest room temperature conductivity of the electrolyte of 8.5 × 10⁻⁷ S/cm was obtained at 30% by weight of LiClO₄. The activation energy, E _a and pre-exponential factor, σ _o, are 1.4 × 10⁻² eV and 1.5 × 10⁻¹¹ S/cm, respectively.     

Li<Subscript>1−<Emphasis Type="BoldItalic">x</Emphasis></Subscript>Sm<Subscript>1+<Emphasis Type="BoldItalic">x</Emphasis></Subscript>SiO<Subscript>4</Subscript> as solid electrolyte for high temperature solid-state lithium batteries

Lithium lanthanoid silicates are projected as promising solid electrolytes for solid-state high-temperature lithium batteries. Synthesis of Li_1−x Sm_1+x SiO₄ (x = 0.2 to 0.6) was carried using sol–gel method, and these compounds were characterized by thermogravimetry differential thermal analysis, X-ray diffraction, Fourier transform infrared, and SEM. Impedance measurements were carried out at different temperatures, and conductivity at different temperatures was calculated. The effect of an increase of samarium content on the conductivity of the solid electrolyte was studied in this paper. It was found that less samarium content exhibits good conductivity at higher temperatures.     

Effects of MnO<Subscript>2</Subscript> nano-particles on the conductivity of PMMA-PEO-LiClO<Subscript>4</Subscript>-EC polymer electrolytes

Li-ion rechargeable batteries based on polymer electrolytes are of great interest for solid state electrochemical devices nowadays. Many studies have been carried out to improve the ionic conductivity of polymer electrolytes, which include polymer blending, incorporating plasticizers and filler additives in the electrolyte systems. This paper describes the effects of incorporating nano-sized MnO₂ filler on the ionic conductivity enhancement of a plasticized polymer blend PMMA–PEO–LiClO₄–EC electrolyte system. The maximum conductivity achieved is within the range of 10⁻³ S cm⁻¹ by optimizing the composition of the polymers, salts, plasticizer, and filler. The temperature dependence of the polymer conductivity obeys the VTF relationship. DSC and XRD studies are carried out to clarify the complex formation between the polymers, salts, and plasticizer.     

Structural,thermal and ion transport studies on nanocomposite polymer electrolyte-{(PEO + SiO<Subscript>2</Subscript>):NH<Subscript>4</Subscript>SCN} system

Development and characterisation of polyethylene oxide (PEO)-based nanocomposite polymer electrolytes comprising of (PEO-SiO₂): NH₄SCN is reported. For synthesis of the said electrolyte, polyethylene oxide has been taken as polymer host and NH₄SCN as an ionic charge supplier. Sol–gel-derived silica powder of nano dimension has been used as ceramic filler for development of nanocomposite electrolytes. The maximum conductivity of electrolyte ∼2.0 × 10⁻⁶ S/cm is observed for samples containing 30 wt.% silica. The temperature dependence of conductivity seems to follow an Arrhenius-type, thermally activated process over a limited temperature range.     

Investigation of ion transport in Li<Subscript>8</Subscript>ZrO<Subscript>6</Subscript> and Li<Subscript>6</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> solid electrolytes

Lithium ionic conductivity and spin-lattice relaxation rates were measured in Li₈ZrO₆ and Li₆Zr₂O₇ solid electrolytes. It was found that the Li₈ZrO₆ solid electrolyte undergoes a transition to the superionic state in the temperature range 673–703 K. It was shown that Li⁺ ions are mobile in particular lattice positions of the Li₆Zr₂O₇ phase, and that ionic conductivity is monotonic at an activation energy of 79.4 kJ/mol.     

Structural and electrical properties of pure and H<Subscript>2</Subscript>SO<Subscript>4</Subscript> doped (PVA)<Subscript>0.7</Subscript>(NaI)<Subscript>0.3</Subscript> solid polymer electrolyte

Solid polymer electrolytes (SPE) based on poly-(vinyl alcohol) (PVA)_0.7 and sodium iodide (NaI)_0.3 complexed with sulfuric acid (SA) at different concentrations were prepared using solution casting technique. The structural properties of these electrolyte films were examined by X-ray diffraction (XRD) studies. The XRD data revealed that sulfuric acid disrupt the semi-crystalline nature of (PVA)_0.7(NaI)_0.3 and convert it into an amorphous phase. The proton conductivity and impedance of the electrolyte were studied with changing sulfuric acid concentration from 0 to 5.1 mol/liter (M). The highest conductivity of (PVA)_0.7(NaI)_0.3 matrix at room temperature was 10⁻⁵ S cm⁻¹ and this increased to 10⁻³ S cm⁻¹ with doping by 5.1 M sulfuric acid. The electrical conductivity (σ) and dielectric permittivity (ε′) of the solid polymer electrolyte in frequency range (500 Hz–1 MHz) and temperature range (300–400) K were carried out. The electrolyte with the highest electrical conductivity was used in the fabrication of a sodium battery with the configuration Na/SPE/MnO₂. The fabricated cells give open circuit voltage of 3.34 V and have an internal resistance of 4.5 kΩ.     

Enhanced ionic conductivity in nano-composite solid polymer electrolyte: (PEG)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> LiBr: <Emphasis Type="Italic">y</Emphasis>(SiO<Subscript>2</Subscript>)

In this paper, we report an enhancement in ionic conductivity in a new nano-composite solid polymer electrolyte namely, (PEG) _x LiBr: y(SiO₂). The samples were prepared, characterized, and investigated by XRD, IR, NMR, and impedance spectroscopy. Conductivity as a function of salt concentration shows a double peak. Five weight percent addition of silica nanoparticles increases the ionic conductivity by two orders of magnitude. Conductivity exhibits an Arrhenius type dependence on temperature. IR study has shown that the existence of nanoparticles in the vicinity of terminal O―H group results in a shift in IR absorption frequency and increase in amplitude of vibration of the terminal O―H group. This might lead to an enhancement in conductivity due to increased segmental motion of the polymer. ⁷Li NMR spectroscopic studies also seem to support this. Thus addition of nanoparticle inert fillers still seems to be a promising technique to enhance the ionic conductivity in solid polymer electrolytes.     

Ionic conduction and effect of cation doping in Tl<Subscript>4</Subscript>HgI<Subscript>6</Subscript>

The ionic conduction properties of undoped and doped Tl₄HgI₆ were investigated using electrical conductivity, dielectrics, differential scanning calorimetry, and X-ray diffraction techniques. The heavy Tl⁺-ions diffusion was activated at high temperature, whereas low conductivity at the lower temperature suggested electronic contribution in undoped Tl₄HgI₆. The partial replacement of heavy Tl⁺ ion by suitable cations (Ag⁺ and Cu⁺) enhanced the conductivity by several orders of magnitude, whereas diminution in conductivity results with increasing dopants’ concentration in Tl₄HgI₆. These results can be interpreted in terms of a lattice contraction and vacancy–vacancy interaction (leading to the cluster formation), respectively. The dielectric values of undoped Tl₄HgI₆ system gradually increasing with temperature, followed by a sharp change, were observed around 385 K and can be explained on the basis of increasing number of space charge polarization and ions jump orientation effects. The activation energy of undoped and doped Tl₄HgI₆ systems were calculated, and it was found that ionic conductivity activation energy for 5 mol% of cation dopants is much lower than that of undoped one, and also 10 mol% doped Tl₄HgI₆ systems.     

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.     

Photoluminescence of nanoparticles of (Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.95</Subscript>(Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0.05</Subscript> solid solution

We have ground bulk samples to obtain nanoparticles of (Ga₂S₃)_1–x (Eu₂O₃) _x solid solutions, the sizes of which were determined using an atomic force microscope. The photoluminescence spectra of the nanoparticles were studied in the temperature interval 77–300 K. We have established the mechanisms for emission and transfer of energy from the matrix to the rare-earth ion, and we determined the Stokes shift (ΔS = 0.7 eV), the Huang–Rhys parameter (S = 16), and the optical phonon energy (ħ−ω = 23 meV).     

Electrical characterization of the [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>][N(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>4</Subscript>]ZnCl<Subscript>4</Subscript> compound

The [N(CH₃)₄][N(C₂H₅)₄]ZnCl₄ compound has been synthesized by a solution-based chemical method. The X-ray diffraction study at room temperature revealed an orthorhombic system with P2₁2₁2 space group. The complex impedance has been investigated in the temperature and frequency ranges 420–520 K and 200 Hz–5 MHz, respectively. The grain interior and grain boundary contribution to the electrical response in the material have been identified. Dielectric data were analyzed using the complex electrical modulus M ^* for the sample at various temperature. The modulus plots can be characterized by full width at half height or in terms of a non-exponential decay function ϕ(t) = exp[(−t/τ) ^β ]. The detailed conductivity study indicated that the electrical conduction in the material is a thermally activated process. The variation of the AC conductivity with frequency at different temperatures obeys the Almond and West universal law.     

Anomalies of the specific heat near the quantum critical point in Tm<Subscript>0.74</Subscript>Yb<Subscript>0.26</Subscript>B<Subscript>12</Subscript>

The behavior of the specific heat near the quantum critical point x ∼ 0.3 in the Tm_{1 − x} Yb _x B₁₂ system has been studied. Detailed measurements have been performed on high-quality single-crystalline Tm_0.74Yb_0.26B₁₂ samples within a wide temperature range of 1.9–300 K in a magnetic field up to 9 T. The temperature dependence of the magnetic contribution to the specific heat has a logarithmic divergence of the form C/T ∼ lnT at T < 4 K, which can be attributed to the quantum critical behavior regime suppressed by the external magnetic field. The Schottky anomaly of the magnetic contribution to the specific heat in Tm_0.74Yb_0.26B₁₂ has been analyzed.     

Electrical properties,equivalent circuit,and dielectric relaxation studies on [(C<Subscript>3</Subscript>H<Subscript>7</Subscript>)<Subscript>4</Subscript>N]<Subscript>2</Subscript>Cd<Subscript>2</Subscript>Cl<Subscript>6</Subscript> polycrystalline

The Ac electrical conductivity and the dielectric relaxation properties of the [(C₃H₇)₄N]₂Cd₂Cl₆ polycrystalline sample have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 209 Hz–5 MHz and 361–418 K, respectively. The purpose is to make a difference between the electrical and dielectric properties of the polycrystalline sample and single crystal. Besides, a detailed analysis of the impedance spectrum suggests that the electrical properties of the material are strongly temperature-dependent. Plots of (Z" versus Z') are well fitted to an equivalent circuit model consisting of a series combination of grains and grains boundary elements. Moreover, the temperature dependence of the electrical conductivity in the different phases follows the Arrhenius law and the frequency dependence of σ (ω) follows the Jonscher’s universal dynamic law. Furthermore, the modulus plots can be characterized by full width at half height or in terms of a nonexperiential decay function φ(t) = exp(t/t)^β. Finally, the imaginary part of the permittivity constant is analyzed with the Cole–Cole formalism.     

Thermoelectric Properties of the TlBiS<Subscript>2</Subscript>-PbS Alloys

High efficiency of thermoelectric conversion can be achieved by using materials with a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Mass-difference-scattering of the phonons is one of the most effective way for reducing the thermal conductivity in bulk thermoelectric materials. Investigations of transport phenomena in (TlBiS₂)_1-x (2PbS)_x alloys system have shown that in solid solutions of the (A³B⁵C ₂ ⁶ )_1-x (2A⁴B⁶)_x type at cation substitution according to scheme 2A⁴⁽⁺²⁾ A ³⁽⁺¹⁾ + B⁵⁽⁺³⁾ occurs a strong decrease of the lattice thermal conductivity. In the vicinity of x = 0. 50 the lattice part of thermal conductivity of (TlBiS₂)_1-x (2PbS)_x alloys decreases down to 0. 26 W/mK, i. e., it approaches the theoretical minimum. As a result, the thermoelectric figure of merit for these alloys ( 25%) exceeds the respective value for lead sulfide at room temperature.     

Composition dependence of density of states in a-Se<Subscript>100−<Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

The present paper reports the DC conductivity measurements at high electric fields in vacuum evaporated amorphous thin films of a-Se_100−x Sn _x (x = 0, 2, 4, 6) glassy alloys. Current-voltage (I–V) characteristics have been measured at various fixed temperatures. In these samples, at low electric fields, ohmic behaviour is observed. However, at high electric fields (E ∼ 10⁴ V/cm), non-ohmic behaviour is observed. An analysis of the experimental data confirms the presence of space charge limited conduction (SCLC) in the glassy materials studied in the present case. From the fitting of the data to the theory of SCLC, the density of defect states (DOS) near Fermi level is calculated. Increase in DOS with increase in Sn concentration has been found which could be correlated with the electronegativity difference between the two elements used here in making the glassy alloys. The peculiar role of the element Sn as an impurity in the pure Se glassy alloy is also discussed.      

Dielectric and polar order behaviors of BaTiO<Subscript>3</Subscript>-Bi(Mg<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics

New perovskite solid solution ceramics of (1−x)BaTiO₃-xBi(Mg_1/2Ti_1/2)O₃ ((1−x)BT-xBMT, x≤0.09) were synthesized by the solid-state reaction technique. X-ray diffraction studies have revealed a stable single perovskite structure for all samples. Dielectric measurements were carried out at different frequencies and temperatures. The polarization evolutions with temperatures were measured to investigate the ferroelectric properties. All the compositions show features of ferroelectrics with diffuse phase transition, though the temperature T _m of their dielectric constant maximum ε _m is frequency dependent. The dielectric constant peak ε(T) of (1−x)BT-xBMT ceramics become broad with increasing BMT content. During the temperature range of ε(T) peak summit, (1−x)BT-xBMT ceramics present quasi-linear dielectric phenomenon under high electric field with very high dielectric constant.     

Structural investigation on PEO-based polymer electrolytes dispersed with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

Thin solid polymer electrolytes based on polyethylene oxide (PEO) and silver triflate (AgCF₃SO₃) dispersed with various concentrations of aluminum oxide (Al₂O₃) nanoparticles have been prepared by solution casting technique. These thin polymer films are found to have thickness of the order of 30 to 100 μm. The X-ray diffraction (XRD) patterns have indicated the amorphous nature of the polymer electrolyte. The differential scanning calorimeter (DSC) traces showed slight change in the glass transition temperature (T _g) whereas the degree of crystallization (X _c) decreases markedly due to the addition of alumina nanoparticles. Fourier transform infrared (FTIR) spectral analysis of all these samples has revealed the presence of absorption bands around 1,000 cm⁻¹; thus indicating the complexation of silver ions with oxygen in PEO. Employing the Wagner’s polarization technique as the standard method, the total ionic transference number for the complexed polymer electrolyte was found to be approximately unity thereby revealing that the significant contribution to electrical conduction was due to ions only. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006     

Effect of ethylene carbonate plasticizer and TiO<Subscript>2</Subscript> nanoparticles on 49% poly(methyl methacrylate) grafted natural rubber-based polymer electrolyte

The effect of plasticizer and TiO₂ nanoparticles on the conductivity, chemical interaction and surface morphology of polymer electrolyte of MG49–EC–LiClO₄–TiO₂ has been investigated. The electrolyte films were successfully prepared by solution casting technique. The ceramic filler, TiO₂, was synthesized in situ by sol-gel process and was added into the MG49–EC–LiClO₄ electrolyte system. Alternating current electrochemical impedance spectroscopy was employed to investigate the ionic conductivity of the electrolyte films at 25 °C, and the analysis showed that the addition of TiO₂ filler and ethylene carbonate (EC) plasticizer has increased the ionic conductivity of the electrolyte up to its optimum level. The highest conductivity of 1.1 × 10⁻³ Scm⁻¹ was obtained at 30 wt.% of EC. Fourier transform infrared spectroscopy measurement was employed to study the interactions between lithium ions and oxygen atoms that occurred at carbonyl (C=O) and ether (C-O-C) groups. The scanning electron microscopy micrograph shows that the electrolyte with 30 wt.% EC posses the smoothest surface for which the highest conductivity was obtained.     

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.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.