G. Govindaraj

Ac conductivity, dielectric studies and conductivity scaling of NASICON materials

Different NASICON systems with general formula Am Bn P3O12 were prepared by melt quenching method, where A � /Na, and B� /Cu, Al, Fe, FeCd. The prepared compounds were characterized by X-ray diffraction, and Fourier transform infrared spectroscopy. The electrical conductivity measurements were made on the different NASICON materials as a function of frequency (20 Hz to 1 MHz) at different temperatures. The bulk conductivity was obtained from the impedance analysis. The dc conductivity activation energies are found to be in the range 0.40 � /1.53 eV. The conductivity and dielectric spectra show the power low feature. The framework of the Almond � /West conductivity formalism is applied to discuss the ac conductivity and determined the dc conductivity sdc, hopping frequency vp, and dimensionless frequency exponent n . The conductivity master curves for the conductivity spectra are obtained by scaling the frequency by (i) vp and (ii) sdcT , where T is temperature in Kelvin. Both types of scaling show same conductivity master curves. # 2002 Published by Elsevier Science B.V.

Effects of differing ratios of network modifier (Ag2O) to network formers (MoO3 + V2O5) and dopant salt (AgI) concentrations in silver-based superionic glassy compounds

Abstract The quaternary AgIAg2OMoO3V2O5 superionic conducting glassy compounds, with different glass modifier Ag2O (M) to glass former MoO3 + V2O5 (F) ratios and with different dopant salt concentrations (AgI), have been prepared by melt quenching and glass-forming compositions are identified. Electrical conductivity measurements are made and it is found that M / F = 1.5 and 60 molecular weight percent of AgI composition of the glassy compound gives the highest conductivity at room temperature (303 K). The conduction mechanism is discussed on the basis of the diffusion path model.

Structure and ion transport in Li3Fe2(PO4)3 synthesized by solution combustion technique

Li3Fe2(PO4)3 is interesting because of its technological application and environmentally benign nature. Nanocrystalline Li3Fe2(PO4)3 is synthesized by a solution combustion technique. The role of fuels/complexing agents in deciding the structural parameters and ac electrical behavior is investigated in this study. Antiferromagnetic nature and direct bandgap energy of 3.09 eV are recognized in the material. Enhanced conduction is established through mobility of Li+ ion in four co-ordination in the modified monoclinic symmetry and high temperature stability through orthorhombic symmetry. Quality of electrical data is confirmed through a Kramers-Kronig test and electrical relaxation parameters are obtained from modulus analysis. Scaling analysis of modulus data confirmed the time-temperature superposition principle.

Scaling behavior in the frequency dependent conductivity of NASICON glasses

Ion dynamic processes in ionically conducting materials have been subject of deep scientific interest for past few years and also it is a challenging problem [1–6]. The studies of electrical relaxation process in ionic conducting solids are very important. The relation between electrical relaxation and glass composition has been studied extensively. Thus, the typical feature of ion dynamical processes has been the remarkable success in developing theories that explain relaxation phenomena in glasses [7–12]. The ion dynamic processes have been studied by electrical conductivity dispersion. In the ion conducting materials the ac conductivity is generally well approximated by [13]

NASICON Materials: Structure and Electrical Properties

Solid electrolytes are one of the functional materials, practically applied in industries because of its high ion conducting property. It provides scientific support for wide variety of advanced electrochemical devices such as fuel cells, batteries, gas separation membranes, chemical sensors and in the last few years, ionic switches. NASICON type ion conductors have been tested widely in energy applications for instance in electric vehicles. High ion conductivity and stability of phosphate units are advantages of NASICON over other electrolyte materials (Hong, 1976). Among the batteries those based on lithium show the best performance.

A.c. conductivity and electric modulus behavior of the vitreous system AgIAg2O[XSeO2(1 − X)V2O5]

Abstract A new quaternary selenovanadate glassy AgIAg 2 O[ X SeO 2 (1 − X )V 2 O 5 ] is prepared and the glass forming regions are determined. An enhancement in conductivity of about one order of magnitude is obtained on adding SeO 2 glass former to the ternary glassy system AgIAg 2 OV 2 O 5 . The results of measurements of a.c. conductivity and dielectric modulus of the glassy system over wide ranges of frequency and temperature are reported. Jonschers dielectric “universal response” formalism is applied to discuss the observed power law dependence of a.c. conductivity. The conductivity relaxation time τ and the power law exponent n are calculated using the relation σ ( ω ) = σ (o)[1 + ( ωτ ) n ] and the results are discussed.

Study of dopant salt concentration in a silver molybdoarsenate glassy system

Abstract Quaternary superionic conducting AgIAg2O(MoO3 + As2O5) glasses with different dopant salt (AgI) contents were prepared by fast quenching of the melt into liquid nitrogen, and characterized by X-ray diffraction. Electrical conductivity studies on pressed pellets are reported. At room temperature (303 K), the highest conductivity, σ = 1.65 × 10 −2 S cm −1 was obtained for the glass with 60 mol.% of AgI. The Ag+ ion concentration and the packing density for glasses were calculated. The conductivity variation with dopant salt is discussed based on the diffusion path model.

Electrical Conductivity Studies of Solution Combustion Synthesized Nanocrystalline Li2NiZrO4 material

A phase‐pure nanocrystalline Li2NiZrO4 material is synthesized by solution combustion synthesis. In this study citric acid is used as fuel and pH of the homogenous solution is maintained. The material is crystallized in a cubic rock‐salt structure of space group Fm□3m. TEM analysis revealed that the material is formed as nano‐crystallites. The structural characterization is accomplished through X‐ray diffraction, thermo gravimetry/differential thermal analysis, transmission electron microscopy and electrical characterization is done through impedance spectroscopy and the results are reported.

Electrical conductivity studies of graphene wrapped nanocrystalline LiMnPO4 composite

Nanocrystalline LiMnPO4 material was synthesized by template free sucrose assisted hydrothermal method. The material possesses the orthorhombic crystal structure with Pnma, space group having four formula units. The GO was prepared by the hummer’s method and it was reduced graphene oxide (rGO) with hydrazine hydrate in the presence of nitrogen atmosphere. LiMnPO4 material was wrapped by the rGO to increase its conductivity. The structural characterization was accomplished through X-ray diffraction, FT-IR and Raman spectroscopy. Morphology was identified by the SEM, Electrical characterization was done through impedance spectroscopy and the results were reported.

The facile synthesis and electrical properties of SiO2/reduced graphene oxide nanocomposite

Reduced Graphene Oxide/SiO2 Nanoparticles were synthesized by a three-step process. First, SiO2 nanoparticles have been synthesized using solvothermal synthesis, and second, graphene oxide is prepared using modified Hummer’s method. Finally, SiO2 nanoparticles have been assembled between graphene oxide layers using hydrothermal synthesis technique. In situ reduction of graphene oxide layers is carried out via thermal reduction during hydrothermal treatment thus avoiding the use of harmful reducing agents. Formation of amorphous SiO2 nanoparticles has been confirmed using X-ray diffraction and scanning electron microscopy. Complex impedance data of SiO2 and SiO2/reduced graphene oxide composite have been modelled using Cole-Cole formalism. Results show that there a decrease of three orders of magnitude in the resistivity of SiO2/reduced graphene oxide composite in comparison to bare SiO2 particles which has a resistivity of an order of 10 5 Ωm.Reduced Graphene Oxide/SiO2 Nanoparticles were synthesized by a three-step process. First, SiO2 nanoparticles have been synthesized using solvothermal synthesis, and second, graphene oxide is prepared using modified Hummer’s method. Finally, SiO2 nanoparticles have been assembled between graphene oxide layers using hydrothermal synthesis technique. In situ reduction of graphene oxide layers is carried out via thermal reduction during hydrothermal treatment thus avoiding the use of harmful reducing agents. Formation of amorphous SiO2 nanoparticles has been confirmed using X-ray diffraction and scanning electron microscopy. Complex impedance data of SiO2 and SiO2/reduced graphene oxide composite have been modelled using Cole-Cole formalism. Results show that there a decrease of three orders of magnitude in the resistivity of SiO2/reduced graphene oxide composite in comparison to bare SiO2 particles which has a resistivity of an order of 10 5 Ωm.