S. A. Suthanthiraraj

Electrical transport and structural properties of new superionic solids in the system (Cu1−xAgxI)–(Ag2O)–(B2O3), (0.05≤x≤0.25)

Abstract Evaluation of electrical transport and structural characteristics of the pseudo ternary system 40(Cu 1− x Ag x I)–45(Ag 2 O)–15(B 2 O 3 ), where 0.05≤ x ≤0.25 has been reported. Electrical conductivity measurements were made using complex impedance method. The extent of contribution of ionic conductivity to the total electrical conductivity in various compositions of the above system was determined by evaluating their ionic transport numbers ( t i ) using Wagners method and the corresponding silver ionic transport numbers ( t Ag + ) by the E.M.F. technique. These measurements have indicated the formation of superionic materials having electrical conductivities of the order of 10 −4 to 10 −3 S cm −1 at room temperature. X-ray diffraction (XRD) analysis, differential scanning calorimetry (DSC) and fourier transform infrared (FT-IR) spectroscopic investigations carried out on these materials have indicated the composite nature of these superionic solids consisting of glassy and crystalline phases. Thermoelectric power (TEP) measurements have also confirmed the positive charge on the conducting species and activation energy for conduction in these materials.

Synthesis of triazole dendrimers with a dimethyl isophthalate surface group and their application to dye-sensitized solar cells

Dendritic architectures with 1,2,3-triazole as the building unit and dimethyl isophthalate as the surface group are synthesized through a convergent approach employing click chemistry and tested for their application in dye-sensitized solar cells (DSSCs). The studies revealed that the presence of triazole and isophthalate groups in dendritic structures significantly altered the absorption, electrochemical and DSSC behaviors. In DSSCs, the dendritic structures exhibited higher Voc values and higher power conversion efficiency (η) in the I−/I3− redox couple under simulated conditions at 40 mW cm−2.

Fast ion transport in the new mixed system (CuI)x·[(Ag2O)2·(V2O5)]100−x (40≤x≤80)

The new mixed system (Cul)x·[(Ag2O)2·V2O5)]100−x where x=40, 45, 50, 55, 60, 65, 70, 75 and 80 mol% was investigated as a possible glassy fast ion conductor by preparing molten mixtures and quenching them to low temperatures. The analysis of their composition was carried out using differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) techniques. These studies have confirmed the formation of new substances. Formation of AgI in some samples was also revealed by XRD analysis and by the occurrence of a characteristic β → α phase transition temperature around 420 K identified through DSC experiments as well. Detailed temperature-dependent a.c. electrical conductivity studies were carried out on the new materials by a.c. impedance analysis in the frequency range 65.5 kHz-1 Hz and over the temperature range 293 to 398 K. It has been found that the highest electrical conductivity of 3.64×10−3 S cm−1 at 305 K due to the migration of Ag+ ions and the lowest activation energy of 0.1 eV in the above temperature range of investigation could be realized for the composition 40CuI-40Ag2O-20V2O5 in the mixed system.

Structural, thermal and transport studies on Ag1 − x Cuxl (0.05 ⩽ x ⩽ 0.25) solid electrolyte

Preparation and characterization studies on polycrystalline samples of Ag1 − xCuxl wherex=0.05, 0.1, 0.15, 0.2 and 0.25, respectively, have been reported. Samples were analysed using powder X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques in order to identify the compositions and phase transition temperatures. A.c. electrical conductivity studies were carried out on pelleted specimens of various compositions in the frequency range 65.5 kHz to 1 Hz and over the temperature range 293–412 K. DSC results obtained in the temperature range 373–473 K have shown that the ß- to α-phase transition temperature is enhanced from 426 K to 438 K whenx is increased from 0.05 to 0.25. XRD results have indicated that there is a shift ind-spacing when the Cul content is increased, suggesting changes in the crystal structure. Typical XRD patterns recorded for the composition Ag0.95Cu0.05l at three different temperatures (room temperature, 373 and 473 K, respectively) have confirmed that both face-centred cubic and hexagonal phases would be present at room temperature and at 373 K as well, whereas at 473 K the structure would be purely body-centred cubic in nature. A.c. impedance analysis of the above samples appears to suggest that their electrical conductivity, predominantly due to the migration of Ag+ ions, lies in the order of 10−4S cm−1 at room temperature.

Evaluation of transport properties of superionic materials in the system (Cu1−xAgxI)–(Ag2O)–(CrO3)

Abstract In the present report, an intensive evaluation of transport properties of superionic materials in a pseudoternary system (Cu 1- x Ag x I)–(Ag 2 O)–(CrO 3 ), where 0.05≤ x ≤0.25, has been described. Room temperature conductivity studies have shown the formation of solid electrolytes with electrical conductivities of the order of 10 −4 to 10 −3 S cm −1 at 295 K. The observed temperature-dependent electrical conductivity behavior is similar to that of conventional solid electrolytes. Impedance and modulus analyses have indicated the temperature-independent distribution of relaxation times and the non-Debye behavior of these materials. The values of silver ionic transport number ( t Ag+ ) obtained by EMF technique are nearly equal to the corresponding ionic transport number ( t i ) values estimated from the Wagners polarization method, thus suggesting the formation of silver ion-conducting solid electrolytes in the chosen system. The present thermoelectric power (TEP) data are found to confirm the formation of silver ion-conducting glassy electrolytes in this system.

Impedance and modulus spectroscopic studies on (CuI)100-x-(Ag2SO4)x (0≤x≤60) mixed system

The frequency-dependent conductivity, σω measurements on (CuI)100-x-(Ag2SO4)x (0≤x≤60) mixed system in the frequency range 1 Hz–65.5 kHz and over the temperature range 293–403 K have been carried out. These studies have illustrated similarities in the behaviour of the present system and the other fast ionic solid systems which are generally found to obey the Jonschers universal power law, σa.c.(ω)=σ0+Aωn, where σa.c.(ω) is the conductivity at frequency ω, σ0 is the limiting zero frequency conductivity or d.c. conductivity and A and n are fitting parameters. The value of n decreases with increasing temperature and A and σ0 increase with temperature (n is a temperature-dependent frequency exponent, A is a frequency-independent and temperature-dependent parameter). These results appear to suggest a mechanism of fast ion conduction due to the presence of well-defined pathways. The strong low-frequency dispersion observed in the case of high conductivity compositions is attributed to the electrode polarization effects. The observed impedance and modulus spectra in correlation with the Arrhenius plots obtained at different frequencies have clearly indicated the frequency dispersion of conduction due to many-body effects and the formation of a large capacitance associated with the electrodes. Thus, the present analysis has suggested a non-Debye type of relaxation process arising due to many-body effects and a distribution of relaxation times, which is a temperature-independent phenomenon exhibited by the heterogeneous electrical structure of the mixed system.

Ultrasmall NiO nanoclusters modified with conical Ni(II)-SR staples for high performance supercapacitor applications

Herein, we report 3-mercaptopropylsulfonate (MPS) stabilized ultrasmall NiO nanoclusters modified with conical Ni(II)-SR staples (NiO@Ni(II)-SR NCs). The surface tuning of MPS (-SR) staples over NiO NCs by varying metal to ligand (M–L) ratio resulted in the size-dependent supercapacitor behaviors. The formation of NiO@Ni(II)-SR NCs was ligand-specific with trace amounts of NaOH in the absence of NaBH4, wherein similar attempts with glutathione (GS) were unsuccessful. Atomic force microscopic (AFM) studies have confirmed the decreasing trend in the sizes of ultrasmall NiO@Ni(II)-SR NCs from ∼10 nm to ∼2 nm on increasing the M–L ratio and that of NiO nanoparticles synthesized with NaBH4i.e. the sizes of the NiO@Ni nanoparticles were found to be much greater (∼250 nm). High resolution scanning electron microscopy (HRSEM) images suggested the presence of lesser NiO aggregates in NiO@Ni(II)-SR NCs than NiO@Ni. X-ray diffraction studies confirm the amorphous nature of the ultrasmall NiO@Ni(II)SR NCs than NiO@Ni nanoparticles. Raman peaks around 510, 740 and 1090 cm−1 validate the presence of Ni–O vibrations, which get intensified with laser exposure, and peaks at 141, 242, 255, 285, 343 cm−1 suggest Ni–S vibrational modes indicating the formation of Ni(II)-SR staples over the core NiO nanoclusters. The specific capacitance (Sc) for NiO@Ni(II)-SR NCs is ∼449 F g−1, which is higher than that of NiO@Ni at 5 mV s−1 by CV analyses. The charge–discharge studies observed a maximum Csp of ∼512 F g−1 at a current density of 1 A g−1, and the cyclic stability for 1000 cycles retained ∼82% of its initial Csp for NiO@Ni(II)-SR NCs.

Synthesis and Dye-sensitized Solar Cell Application of Polyolefinic Aromatic Molecules with Pyrene as Surface Group

Synthesis of polyolefinic aromatic molecules with pyrene as the surface group, and their role as an additive in the redox couple of dye-sensitized solar cells, is described. The studies yield a promising power conversion efficiency of 5.27% with a short circuit current density of 6.50 mA cm–2, an open circuit voltage of 0.60 V, and a fill factor of 0.54 under 40 mW cm–2 simulated air mass (A.M.) 1.5 illumination. Most importantly, the photocurrent responsivity increases with an increase in the number of pyrene units on the surface.

Complex impedance and structural analyses of the mixed system 40(Cu1−xAgxI)–30(Ag2O)–30(SeO2), (0.05≤x≤0.25)

Abstract Using complex impedance analysis, temperature-dependent electrical conductivity studies of various compositions of the mixed system 40(Cu 1− x Ag x I)–30(Ag 2 O)–30(SeO 2 ), (0.05≤ x ≤0.25) over the temperature region 295–445 K have been carried out. All the chosen compositions of the system exhibit Arrhenius type of conductivity as a function of temperature and their activation energies for conduction lie in the range 0.27–0.42 eV. The values of ionic transport number of these materials are greater than 0.96. The presence of AgI in these materials has been inferred from the β→α phase transition of AgI, which is characterized by an endothermic peak at around 416 K in the DSC traces of these specimens. While the structural analysis carried out by means of X-ray diffraction has revealed the formation of AgI, Ag 2 SeO 4 and new phases involving glassy and crystalline compounds, the Fourier transform infrared (FTIR) spectroscopic results have indicated the presence of SeO 4 2− , SeO 3 2− and Se 2 O 7 2− species thus confirming the ionic nature of the phases.

Impedance spectroscopic analysis of crystalline solid electrolytes in the mixed system (CuI)100 − x (Ag4P2O7)x (0 ≤ x ≤ 60)

Abstract The frequency-dependent impedance analysis was carried out on the (CuI) 100 − x -(Ag 4 P 2 O 7 ) x (0 ≤ x ≤ 60) mixed system in the range from 1 Hz to 65.5 kHz and over the temperature range 293–393 K. The frequency-dependence of the conductivity of various compositions, explained on the basis of the Jonschers universal power law ascribed the high frequency dispersion to many body effects arising due to ion-ion interaction within the multiphase system and the low frequency dispersion to the electrode polarization effect. Effectively, the modulus spectra suggested a non-Debye type of relaxation process with a temperature-independent distribution of relaxation times (DRT) and the heterogeneous electrical structure of the present multiphase system.