Ravindra Kumar Gupta

Estimation of energies of Ag+ ion formation and migration using transient ionic current (TIC) technique

Abstract Transient ionic current (TIC) and impedance spectroscopy techniques were employed to measure the Ag+ ion mobility (ω) and conductivity (σ) respectively of AgI in both β- and α-phases. Subsequently, the mobile ion concentration (n) was calculated using σ and μ data. σ, μ and n show thermally activated type behaviour in both the regions of the phase transition. From the log μ versus 1/T and log n versus 1/T Arrhenius plots, the energies of migration and formation of mobile silver ion were estimated as 0.14 and 0.15 eV respectively in the β-phase and 0.05 and 0.006 eV respectively in the α-phase. The extremely low value of energy of formation in the α-phase suggested that a negligibly small number of mobile ions is thermally added to the large n already existing in this phase. On the basis of these experimental studies, it is concluded that the large increase of σ in αAgI is predominantly due to an abrupt increase of mobile ion concentration. The contribution of ionic mobility to the total conductivity is small.

Effects of pH and Dye Concentration on the Optical and Structural Properties of Coumarin-4 Dye-Doped SiO2-PDMS Xerogels

Optical and structural properties of coumarin-4 dye-doped SiO2-PDMS xerogels synthesized by acid catalyzed (one-step) and acid-base catalyzed (two-step) sol-gel routes with varying pH (0.6 to 7) and dye content ( 5 × 10−4 to 5 × 10−2 mole) are reported. Spectroscopic methods such as photo-luminescence, FT-IR and FT-Raman were used for characterizations. The acid catalyzed xerogels prepared with pH < 2.5 exhibited two fluorescence peaks, I at ∼390 nm and II at ∼480 nm. The acid-base catalyzed xerogels synthesized with pH < 2.5 also exhibited two peaks, I at ∼400 nm and II at ∼475 nm. Peak II was not observed for the samples with pH ≥ 2.5. This phenomenon was attributed to the existence of pH dependent different forms of coumarin-4 molecule. The concentration-quenching phenomenon was observed for the acid catalyzed xerogels prepared with different dye concentration. TheFT-IR spectra indicated the existence of hydrogen bonds between the carbonyl groups of dye molecules and the silanol groups of gel matrix. The hydrogen bonding was the highest for the samples with the extremity pH, 0.6 and 7, resulting in the highest dye/gel matrix interactions, hence, the highest fluorescence peaks. The Raman studies indicated that the samples prepared with pH < 2.5 possessed relatively more number of 3-membered siloxane rings than 4-membered siloxane rings. The ring statistics was reversed for the samples with pH > 2.5. The number of silanol groups was higher for the samples with pH > 2.5.

Poly(ethylene oxide):succinonitrile—a polymeric matrix for fast-ion conducting redox-couple solid electrolytes

A blend of poly(ethylene oxide), PEO, and succinonitrile, SN, was investigated for the first time for applying it as a polymeric matrix of low-cost and thermally stable fast-ion conducting redox-couple solid polymer electrolytes. The PEO–SN blend in equal weight fraction showed room temperature ionic conductivity of 1 × 10−8 S cm−1 with nearly two orders of magnitude higher than that of PEO due to reduced crystallinity. The blend resulted in a solid electrolyte with improved ionic conductivity of ~7 × 10−4 S cm−1 at 25 °C. The blend and its electrolyte showed thermal stability up to 100 °C, which is essential for outdoor application of dye-sensitized solar cells.

Transport properties of a new Li+ ion-conducting ormolyte: (SiO2-PEG)-LiCF3SO3

The transport properties of a new fast Li+ ion-conducting sol–gel-derived ormolyte, (SiO2–10 wt% PEG)–[Li/O] LiCF3SO3, with [Li/O] = 0–0.1 (mol/mol), is reported. The composition with [Li/O] = 0.04 exhibited the highest conductivity (σ25 °C = 1 × 10−4 S cm−1), with an enhancement of 103 over the host matrix (SiO2–10 wt% PEG xerogel), and has been found to be the ‘optimum conducting composition’. Direct determination of Li+ ion mobility (μ) and mobile ion concentration (n) revealed that the enhancement was due to the increase in both μ and n. Studies of the variation of σ, μ, and nversus temperature indicated that the system shows Arrhenius-type behavior. The activation energy and energies of migration and formation were evaluated from their respective Arrhenius plots. Measurement of the ion transference number (tion) confirmed that the ions are the sole charge carriers in the system. These results are discussed in the light of existing theories.

Transport property and battery discharge characteristic studies on 1−x(0.75Agl∶0.25AgCl)∶ xAl2O3 composite electrolyte system

Various experimental studies on a new fast Ag+ ion-conducting composite electrolyte system: (1−x) (0.75Agl∶0.25AgCl)∶xAl2O3 are reported. Undried Al2O3 particles of size <10 Μm were used. The conventional matrix material Agl has been replaced by a new mixed 0.75Agl∶0.25AgCl quenched and/or annealed host compound. Conductivity enhancements ∼10 from the annealed host and ∼3 times from the quenched host obtained for the composition 0.7(0.75Agl∶0.25AgCl)∶0.3Al2O3, can be explained on the basis of the space charge interface mechanism. Direct measurements of ionic mobility Μ as σ function of temperature together with the conductivity σ were carried out for the best composition. Subsequently, the mobile ion concentration n values were calculated from Μ and a data. The value of heat of ion transport q* obtained from the plot of thermoelectric power θ versus 1/T supports Rice and Roths free ion theory for superionic conductors. Using the best composition as an electrolyte various solid state batteries were fabricated and studied at room temperature with different cathode preparations and load conditions.

[0.75AgI :0.25AgCl] quenched system: a better choice as host compound in place of AgI to prepare Ag+ ion conducting superionic glasses and composites

Abstract Various transport properties, namely, the electrical conductivity, σ, ionic transference number, tion, ionic mobility, μ, etc. were measured for the quenched [0.75AgI:0.25AgCl] system. The mobile ion concentration, n, was calculated using σ and μ data. The results were compared with the values for AgI. The quenched [0.75AgI:0.25AgCl] system exhibited a β → α like transition in the log σ versus 1/T plot at ∼ 135°C identical to AgI. The present investigations suggest that the quenched [0.75AgI:0.25AgCl] mixed system is a better choice as a host compound in place of AgI to prepare Ag+ ion conducting superionic glasses and composites. Using the quenched [0.75AgI:0.25AgCl] system as host, the following superionic solid systems were prepared and studied: (A) (1) x[0.75AgI:0.25AgCl] : (1 − x)[Ag2O · B2O3], (2) x[0.75AgI : 0.25AgCl] : (1 − x)[Ag2O · B2O3], (by the mellt-quenched method (glass systems)); (B) (1) (1 − x)[0.75AgI:0.25AgCl]: x Al2O3 (by dispersing second-phase particles of size (

Characterization of basic transport properties in a new fast Ag+ ion conducting composite electrolyte system : (1 - x)[0.75AgI :0.25AgCl] :xZrO2

Abstract Studies of some basic ionic transport properties of a new fast Ag+ ion conducting two-phase composite electrolyte system: (1−x)[0.75AgI:0.25AgCl]:xZrO2, where 0≤x≤0.5 (in molar weight fraction), are reported. A ‘quenched/annealed [0.75AgI:0.25AgCl] mixed system/solid solution’ has been used as a first phase host matrix salt as an alternative to the traditional host AgI, while particles (≤5 μm) of the insulating and inert ZrO2 were dispersed as second phase dispersoid. In order to find the ‘optimum conducting composition’ (OCC), different compositions of the two phases were mixed homogeneously adopting various routes of preparation. The phase identification studies revealed the coexistence of separate phases. The temperature-dependent transport property studies were carried out on OCC employing various techniques. The mechanism of ion transport has been explained on the basis of models proposed for two two-phase composite electrolyte systems.

Investigation on transport properties of the silver ion conducting composite electrolyte

We report here a conductivity enhancement (∼101) at room temperature in a new Ag+ ion conducting composite system. Two silver halides AgI and AgCl, in the mol.wt.(%) ratio 75:25 were taken as first phase host compound for the first time. Inert second phase Al2O3 particles of size<10 μm were dispersed in varying molar proportions in the first phase. The highest enhancement in the conductivity (∼9.2×10−4S/cm) was obtained for the ratio: 0.7[0.75AgI·0.25AgCl]·0.3Al2O3. The plot of electrical cond uctivity as a function of temperature for the best composition indicated the presence of characteristics β→α-like transition of AgI or host compound in the composite system with slightly decreased conductivity values from the host in the α-phase. The equations governing log σ versus 1/T for the composite system are represented by: σ=0.016 exp(−0.074/kT)→β-like phase; σ=0.041 exp(−0.024/kT)→α-like phase give the activation energies as 0.074 eV and 0.024 eV in β and α-like phases, respectively, as compared to the values 0.24 eV and 0.025 eV for the host material. The low activation energy value in the β-region suggest easy ion migration in the composite system. The ionic mobility μ∼(2.37±1)×10−2cm−2/Vs) was evaluated at room temperature for the best composition using the transient ionic current (TIC) technique, while the value of the transference number tions is close to unity as obtained by two different techniques, i.e. Wagners dc polarisation and electrochemical cell potential measurements. For the host material tion and μ(1.5±1)×10−2.

Structural study of a sol–gel derived novel solid oxide fuel cell perovskite: (La1−xSrx)(Cr0.85Fe0.05Co0.05Ni0.05)O3−δ

The effect of composition on the structure of the new solid oxide fuel cell (SOFC) perovskite (La1−x Srx )(Cr0.85Fe0.05Co0.05Ni0.05)O3−δ is studied using x-ray diffractometry, pycnometry, and Fourier-transform infrared and Raman spectroscopy. Samples were synthesized using the Pechini method via doping the La site with Sr 2+ , to a composition with x = 0‐0.4 mole fraction, and at the Cr site with 0.05 mol of Co 2+ , Fe 2+ and Ni 2+ , and the structural results were compared with those for orthorhombic LaCrO3 .T he samples were orthorhombic perovskite of the Pnma space group. A second phase, monoclinic SrCrO4, was also observed, whose content increased linearly with increasing x. A large decrease in the lattice and hence volume was observed for the sample with x = 0.1, which was accompanied by a sharp decrease in the Cr−O bond length, tilt angle and crystallite size. The structural parameters were almost invariant for x = 0.1‐0.4, probably due to an increase in content of the high valence cations of smaller ionic radii, as suggested by an increase in the intensity of the defect band (∼515 cm −1 , IR). The octahedral CrO6 stretching, bending and tilting modes were found shifted accordingly. A mechanism employing a partial-charge model was proposed to explain the results. (Some figures in this article are in colour only in the electronic version)

Ion transport and solid state battery studies on a new silver molybdate superionic glass system: x[0.75AgI: 0.25AgCl]: (1-x)[Ag2O: MoO3]

Preparation, material characterization, ion transport and battery discharge characteristic studies are reported for a new silver molybdate glass system: x[0.75AgI: 0.25AgCl]: (1-x)[Ag2O: MoO3], where 0<x<1 in molar weight fraction. The traditional host AgI has been replaced by an alternate compound: “a quenched [0.75AgI: 0.25 AgCl] mixed system/solid solution”. Electrical conductivity (σ), ionic mobility (μ) and mobile ion concentration (n) measurements were carried out as a function of “x”. The composition: 0.8[0.75AgI: 0.25AgCl]: 0.2[Ag2O: MoO3] exhibited the highest conductivity (∼ 6×10−3 S·cm−1) at room temperature and has been referred to as ‘optimum conducting composition (OCC)’. The compositional variation of “μ” and “n” revealed that the enhancement in the room temperature conductivity of OCC is predominantly due to the increase in mobile ion concentration. The XRD and DSC analysis on OCC indicated the formation of glassy phase with partial presence of unreacted polycrystalline phase of the host salt. The temperature dependence of various ionic transport parameters viz. “σ”, “μ”, “n” and ionic transference number (tion) were carried out on the OCC and the results have been discussed on the basis of theoretical models suggested for superionic glasses. In addition to this, solid state batteries were fabricated using OCC as electrolyte and discharge characteristics were studied under varying load conditions.