Effect of molecular weight of PMMA on the conductivity and viscosity behavior of polymer gel electrolytes containing NH<Subscript>4</Subscript>CF<Subscript>3</Subscript>SO<Subscript>3</Subscript>

The addition of polymethyl methacrylate (PMMA) having different molecular weights to electrolytes containing ammonium trifluoromethanesulfonate (NH₄CF₃SO₃) in diethyl carbonate (DEC) has been found to result in conductivity enhancement and to yield gel electrolytes with conductivity higher than the corresponding liquid electrolytes. The increase in conductivity has been found to be due to the dissociation of undissociated NH₄CF₃SO₃ and ion aggregates present in the electrolytes, and this has been supported by Fourier transform infrared spectroscopy results, which suggests active interaction of PMMA and NH₄CF₃SO₃ in these gel electrolytes. The increase in conductivity also depends upon the molecular weight of the polymer used and is relatively more for PMMA having lower molecular weight. The increase in viscosity with PMMA addition also depends upon the molecular weight of the polymer and is closely related to the conductivity behavior of these electrolytes. Polymer gel electrolytes have been found to be thermally stable up to a temperature of 125 °C.     

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     

Effects of various LiPF<Subscript>6</Subscript> salt concentrations on PEO-based solid polymer electrolytes

In this research, various weight percents of LiPF₆ are incorporated into PEO-based polymer electrolyte system. Thin film electrolytes are prepared via solution casting technique and characterized by FTIR, XRD and DSC analyses in order to study their complex behaviour. The amorphicity of the electrolytes are measured by DC impedance. The results reveal that the conductivity increases with increasing temperature when the salt concentration increases to 20 wt.%. The conductivity for 20 wt.% of salt remains similar to the conductivity of 15 wt.% of salt at 318 K. Impedance studies show that the conductivity increases with increasing LiPF₆ concentration, whereas XRD studies reveal that the phase changes from crystalline to amorphous when LiPF₆ concentration increases. DSC studies indicate a decrease in T _m with increasing LiPF₆ concentration. Finally, the complexation process is examined using FTIR.     

Hydrothermal synthesis of pure LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> from nanostructured MnO<Subscript>2</Subscript> precursors for aqueous hybrid supercapacitors

Pure LiMn₂O₄ samples with high crystallinity (LMO-1# and LMO-2#) were successfully synthesized by a facile hydrothermal method using δ-MnO₂ nanoflowers and α-MnO₂ nanowires as the precursors. The as-prepared samples were analyzed by XRD, SEM, and Brunauer-Emmett-Teller (BET), and their capacitive properties were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge test. Two LiMn₂O₄ samples showed good capacitive behavior in aqueous hybrid supercapacitors. AC//LMO-1# and AC//LMO-2# delivered the initial specific capacitance of 45.4 and 40.7 F g^?1 in 1 M Li₂SO₄ electrolyte at a current density of 200 mA g^?1 in the potential range of 0～1.5 V, respectively. After 1000 cycles, the capacitance retention was 97.6% for AC//LMO-1# and 93.7% for AC//LMO-2#. Obviously, LMO-1# from δ-MnO₂ nanoflowers exhibited higher specific capacitance and better cycling performance than LMO-2#, so LMO-1# was more suitable as the positive electrode material in hybrid supercapacitors.     

Effect of an interface boundary on the magnetooptical and magnetotransport properties of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>/La<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> heterostructures

The optical, magnetooptical (Kerr effect and magnetotransmission), and magnetotransport properties of La_2/3Ca_1/3MnO₃/La_2/3Sr_1/3MnO₃ and La_2/3Ca_1/3MnO₃/SrTiO₃/La_2/3Sr_1/3MnO₃ heterostructures on SrTiO₃ substrates are studied. The contribution of the interface boundary to the magnetotransmission is typical of a material with a transitional composition. It is found that a 2-nm-thick SrTiO₃ spacer does not influence the shape and position of the magnetotransmission peak in a field normal to the surface of the heterostructure but increases the contribution of the upper layer to the magnetotransmission in the Voigt geometry and also enhances the magnetoresistance that is due to the tunneling of spin-polarized carriers through the spacer. The Kerr spectra taken of the heterostructures are typical of single-layer single-crystal films.     

Magnetic behaviour of nano-particles of Fe<Subscript>2.9</Subscript>Zn<Subscript>0.1</Subscript>O<Subscript>4</Subscript>

DC magnetization measurements are reported in the temperature range 20–100 K on a poly-disperse nano-particle sample of the spinel ferrite Fe_2.9Zn_0.1O₄ with a log-normal size distribution of median diameter 43.6 Å and standard deviation 0.58. Outside a core of ordered spins, moments in surface layer are disordered. Results also show some similarities with conventional spin glasses. Blocking temperature exhibits a near linear variation with two-third power of the applied magnetic field and magnetizationM evolves nearly linearly with logarithm of timet. Magnetic anisotropy has been estimated by analysing theM-logt curve. Anisotropy values show a large increase over that of bulk particle samples. Major contribution to this enhancement comes from the disordered surface spins.     

Optical and magnetotransport properties of the Nd<Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript>MnO<Subscript>3</Subscript>-Sm<Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript>MnO<Subscript>3</Subscript> heterostructure

The effects of magnetotransmission and magnetoresistance in a film heterostructure composed of manganite layers with different Curie temperatures have been analyzed. High sensitivity of optical methods to the presence of different magnetic phases in the bulk of the material has been shown.     

High-temperature conductivity and structure of Y<Subscript>2</Subscript>(WO<Subscript>4</Subscript>)<Subscript>3</Subscript> ceramics

The magnitude and character of conductivity were studied for Y₂(WO₄)₃ ceramics synthesized by the ceramic (from oxides) and organic-nitrate procedures. Investigation of the dependence \(\sigma \left( {{\alpha _{{o_2}}}} \right)\) and measurements of the ion transport numbers of charge carriers by the EMF method showed that Y₂(WO₄)₃ is basically an ion conductor. The conductivity is largely determined by the sample preparation conditions related to the dependence of the specific surface area and powder grain size on the synthetic procedure. The maximum high-temperature conductivity of Y₂(WO₄)₃ was 2.51 × 10^–4 S/cm, which roughly corresponds to the conductivities of Sc₂(WO₄)₃ and In₂(WO₄)₃ measured under the same conditions. It was confirmed that Y₂(WO₄)₃ crystallizes as a mixed monoclinic-orthorhombic structure at 1000°C. The character of water incorporation in hydrated Y₂(WO₄)₃ crystals was studied by thermogravimetry and diffuse reflectance IR spectroscopy. A qualitative model of water intercalation was suggested.     

Magnetic behaviour of nano-particles of Fe<Subscript>2.8</Subscript>Zn<Subscript>0.2</Subscript>O<Subscript>4</Subscript>

Magnetization measurements are reported on a nano-particle sample of Znsubstituted spinel ferrite Fe_2.8Zn_0.2O₄ in the temperature range 20–300 K. Analysis of small-angle neutron scattering data shows the sample to have a log-normal particle size distribution of median diameter 64.4 Å and standard deviation 0.38. Magnetization evolves over a long period of timet going nearly linearly with logt. Magnetic anisotropy, estimated by fitting M-logt curve, shows many fold increase over that of bulk particle sample. Major enhancement owes to disordered moments in surface layer. In the nano-particle state as well increasing amount of Zn causes anisotropy to decrease.     

Sm<Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript>MnO<Subscript>3</Subscript>/Nd<Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript> MnO<Subscript>3</Subscript> heteroepitaxial structure: Optical and magnetotransport properties

Sm_0.55Sr_0.45MnO₃/Nd_0.55Sr_0.45MnO₃ heterostructure consisting of layers with different Curie temperatures is studied. By comparing data for IR transmission, resistivity, magnetotransmission, magnetoresistance, and Kerr effect measured on the side of the film and substrate, the Curie temperatures of the layers are determined and the contributions of the layers to the magnetoresistance and magnetotransmission are estimated. A weak temperature dependence of the magnetotransmission and magnetoresistance makes manganites with a colossal magnetoresistance and magnetotransmission candidate materials for devices without temperature stabilization.     

Thermal properties and ionic conductivity of Li<Subscript>1,3</Subscript>Ti<Subscript>1,7</Subscript>Al<Subscript>0,3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> solid electrolytes sintered by field-assisted sintering

Li_1,3Ti_0,7Al_0,3(PO₄)₃ (LATP) powder was obtained by a conventional melt-quenching method and consolidated by field-assisted sintering technology (FAST) at different temperatures. Using this technique, the samples could be sintered to relative densities in the range of 93 to 99 % depending on the sintering conditions. Ionic and thermal conductivity were measured and the results are discussed under consideration of XRD and SEM analyses. Thermal conductivity values of 2 W/mK and ionic conductivities of 4?×?10^?4 Scm^?1 at room temperature were obtained using relatively large particles and a sintering temperature of 1000 °C at an applied uniaxial pressure of 50 MPa.     

Magnetic and electric properties of Eu<Subscript>0.62</Subscript>Bi<Subscript>0.38</Subscript>MnO<Subscript>3</Subscript> and Eu<Subscript>0.53</Subscript>Bi<Subscript>0.32</Subscript>Sr<Subscript>0.15</Subscript>MnO<Subscript>3</Subscript> crystals

Single crystals of Eu_0.62Bi_0.38MnO₃ and Eu_0.53Bi_0.32Sr_0.15MnO₃ solid solutions crystallizing in an orthorhombically distorted perovskite structure were prepared. At temperatures above 120 K, Eu_0.62Bi_0.38MnO₃ exhibits the properties of structural glass while remaining a dielectric at all temperatures. There is no long-range magnetic order in this compound. Eu_0.53Bi_0.32Sr_0.15MnO₃ behaves as a semiconductor above 120 K and exhibits a jump in conductivity at T = 175 K associated with a metal-insulator transition occurring within limited regions of the crystal. In these regions, there appears a ferromagnetic moment (due to double exchange mediated by charge carriers) and local electric polarization.     

Effect of ethylene carbonate plasticizer on agar-agar: NH<Subscript>4</Subscript>Br-based solid polymer electrolytes

Proton-conducting polymer electrolytes based on biopolymer, agar-agar as the polymer host, ammonium bromide (NH₄Br) as the salt and ethylene carbonate (EC) as the plasticizer have been prepared by solution casting technique with dimethylformamide as solvent. Addition of NH₄Br and EC with the biopolymer resulted in an increase in the ionic conductivity of polymer electrolyte. EC was added to increase the degree of salt dissociation and also ionic mobility. The highest ionic conductivity achieved at room temperature was for 50 wt% agar/50 wt% NH₄Br/0.3% EC with the conductivity 3.73?×?10^?4 S cm^?1. The conductivity of the polymer electrolyte increases with the increase in amount of plasticizer. The frequency-dependent conductivity, dielectric permittivity (ε′) and modulus (M′) studies were carried out.     

Thermal conductivity of Na<Subscript>2</Subscript>W<Subscript>2</Subscript>O<Subscript>7</Subscript> crystal

The thermal conductivity of Na₂W₂O₇ single crystal has been studied along the main crystallographic directions at temperatures of 50–573 K. A low thermal conductivity is found to correlate with a significant difference in the cation weight.     

Asymmetric capacitors based on TiO<Subscript>2</Subscript> and mesoporous MnO<Subscript>2</Subscript> electrodes using neutral aqueous electrolyte

Asymmetric capacitor based on TiO₂ with the size range from 90 to 410 nm and mesoporous MnO₂ (ca. 200–380 nm) electrodes has been successfully constructed and characterized in LiClO₄ aqueous electrolyte. The samples of both metal oxides were fully characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption, and so on. The electrochemical capacitive performances of both electrode materials were evaluated by cyclic voltammetry and galvanostatic charge-discharge in 1 mol/L LiClO₄ with a working voltage of 2.0 V. The discharge profile of the asymmetric capacitor exhibited an excellent capacitive behavior and good cycling stability after 2000 cycles. Moreover, the TiO₂//MnO₂ asymmetric capacitor possesses both higher energy density and power density (7.7 Wh/kg, 762.5 W/kg) than that of Maxsorb//Maxsorb symmetrical capacitor (7.0 Wh/kg, 400.0 W/kg).

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Graphical abstract A novel asymmetric capacitor based on TiO₂ and mesoporous MnO₂ electrodes has been successfully constructed and characterized in LiClO₄ aqueous electrolyte.

     

Preparation of MnO<Subscript>2</Subscript>/WMNT composite and MnO<Subscript>2</Subscript>/AB composite by redox deposition method and its comparative study as supercapacitive materials

The manganese oxide/multi-walled carbon nanotube (MnO₂/MWNT) composite and the manganese oxide/acetylene black (MnO₂/AB) composite were prepared by translating potassium permanganate into MnO₂ which formed the above composite with residual carbon material using the redox deposition method and carbon as a reducer. The products were characterized by X-ray diffraction, Fourier transform infrared, and scanning electron microscope. Electrochemical properties of both the MnO₂/MWNT and MnO₂/AB electrodes were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the MnO₂/MWNT electrode has better electrochemical capacitance performance than the MnO₂/AB electrode. The charge–discharge test showed the specific capacitance of 182.3 F·g⁻¹ for the MnO₂/MWNT electrode, and the specific capacitance of 127.2 F·g⁻¹ for the MnO₂/AB electrode had obtained, within potential range of 0–1 V at a charge/discharge current density of 200 mA·g⁻¹ in 0.5 mol·L⁻¹ potassium sulfate electrolyte solution in the first cycle. The specific capacitance of both the MnO₂/MWNT and MnO₂/AB electrodes were 141.2 F·g⁻¹ and 78.5 F·g⁻¹ after 1,200 cycles, respectively. The MnO₂/MWNT electrode has better cycling performance. The effect of different morphologies was investigated for both MnO₂/MWNT and MnO₂/AB composites.     

Effect of a magnetic field on the permittivity of 80%La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/20%GeO<Subscript>2</Subscript> composite

The dielectric properties of a magnetoresistive conducting two-phase 80%La_0.7Sr_0.3MnO₃/20%GeO₂ (wt %) composite have been studied near the percolation threshold in magnetic fields from 0 to 15 kOe at frequencies of the measurement field from 5 kHz to 1 MHz. The samples have inductive impedances; i.e., their permittivities can be considered negative due to a high conductivity in this frequency range. The permittivity increases in magnitude in magnetic field, and the values of the magnetodielectric coefficient reach 23% at room temperature. The reasons for the effect of magnetic field on the dielectric permittivity of samples are discussed.     

NO<Subscript>2</Subscript>-sensing properties of La<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>MnO<Subscript>3</Subscript> synthesized by self-propagating combustion

Ultrafine-structure La_0.65Sr_0.35MnO₃ (LSM) powders synthesized by self-propagating combustion method have been used to fabricate sensing electrodes (SEs) for NO₂ mixed-potential sensors based on yttria-stabilized zirconia (YSZ). This type of sensor was found to provide better NO₂ sensitivity at 500 °C than sensors with LSM powders synthesized by traditional solid-state methods. The response values of the sensor have good linear relationship (sensitivity 36.6 mV/decade and linear fit 0.99) with the logarithm of NO₂ concentration varying from 30 to 500 ppm. The influence of sintering temperature (1000, 1100, 1200, and 1300 °C) on sensor response was also examined and was found to have a significant effect on the morphology of LSM-SEs. Moreover, in the presence of NO, CO₂, CO, and NO₂, the sensor exhibited good NO₂ selectivity.