V. Thangadurai

External-Stimuli Responsive Photophysics and Liquid Crystal Properties of Self-Assembled “Phosphole-Lipids”

A series of new amphiphilic phosphonium materials that combine the electronic features of phospholes with self-assembly features of lipids were synthesized. Variable concentration/temperature and 2D NMR studies suggested that the systems undergo intramolecular conformation changes between a closed and open form that are triggered by intermolecular interactions. The amphiphilic features of the phospholium species also induce liquid crystalline and soft crystal phase behavior in the solid state, which was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and variable temperature powder X-ray diffraction (VT-PXRD). The studies revealed that both conjugated backbones and counteranions work together to organize the systems into different morphologies (liquid crystal/soft crystal). Dithieno[3,2-b:2,3-d]phosphole-based compounds exhibit enhanced emission in the solid state and at low temperature in solution due to aggregation-induced enhanced emission (AIEE). Photoinduced electron transfer (PET) induced via the alkoxybenzyl group at the phosphonium center in the fused-ring systems can be effectively suppressed through intermolecular charge transfer (ICT) processes within the main scaffold of a nonfused system, which was confirmed by static and dynamic fluorescence spectroscopy. The dynamic features of these new materials also endow the systems with external-stimuli responsive photophysical properties that can be triggered by temperature and/or mechanical forces.

Use of simple ac technique to determine the ionic and electronic conductivities in pure and Fe-substituted SrSnO3 perovskites

Abstract We report the use of a new method to separate the ionic and electronic contributions to the conduction of solids that involves the use and proper interpretation of low amplitude variable frequency ac measurements. This is a relatively simple technique and has some advantages over the dc methods that are normally employed for this purpose, the Tubandt Faraday’s Law method, the dc assymetric polarization technique that is often called the Hebb–Wagner method, and the dc open circuit potential method. The temperature dependence of the transference numbers of several members of the SrSnO 3 family of perovskite-like oxides, both with and without Fe substitution for some of the Sn, determined by this new method are reported.

Solid state lithium ion conductors: Design considerations by thermodynamic approach

The most common previously employed methods of designing useful solid state lithium ion conductors (SSLICs) are reviewed and a new approach for the rational design of advanced SSLICs is described, which makes use of thermodynamic considerations. The described method is based on the Gibbs energy of formation of binary compounds of substitutional or additional cations (including dopants) and is demonstrated by the improvement of the lithium ion conductivity of SSLICs having perovskite-, NASICON- and Li4SiO4-type structures. Dopant metal oxides with higher negative Gibbs energies of formation than that of the parent metal oxide increase commonly the lithium ion conduction. The stronger binding forces of the oxide ion with the dopant cation result in an electrostatic shielding of the attractive forces between the lithium ions and the anions which facilitates the ionic motion. Irrespective of the crystal structure, it is expected that this thermodynamic rule holds also for other mobile ionic species.

Tailoring ceramics for specific applications: A case study of the development of all-solid-state lithium batteries

AbstractMetal oxides with the nominal chemical compositions Li5La3M2O12 (M=Nb, Ta), possessing a garnet-like structure, exhibit ionic bulk conductivities of the order of magnitude of ∼10−6 S/cm at 25 °C. Partial substitution of La by alkaline earth elements (Ca, Sr, Ba) in Li5La3M2O12 yields new members of compounds with garnet-like structure with the composition Li6ALa2M2O12 (A=Ca, Sr, Ba). Among the investigated compounds, so far, the Ba-compound Li6BaLa2Ta2O12 exhibits the highest bulk conductivity of 4.0×10−5 S/cm at 22 °C with an activation energy of 0.40 eV. All Ta-members were found to be stable against chemical reaction with molten elemental lithium. Li6ALa2Ta2O12 (A=Sr, Ba) exhibit also high electrochemical stability of ∼6 V vs. lithium and chemical stability against reaction with LiCoO2 cathode material.A novel high voltage thin-film battery was constructed using spinel-type Li2MMn3O8 (M=Co, Fe) as positive electrode, LiPON as electrolyte and Al as negative electrode material. Li2MMn3O8 (M=Fe, Co) electrodes show two reversible plateaus during the charging and discharging cycle at ∼4 and ∼5 V vs. Li. The former plateau is due to the valence change of Mn3+ to Mn4+ and the latter one is due to the oxidation of M3+ to M4+. The chemical diffusion coefficient (n

Mixed oxide ion and electronic conductivity in perovskite-type SrSnO3 by Fe substitution

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New lithium-ion conductors based on the NASICON structure

n) was found to be in the range 10−13–10−12 cm2/sec for any composition x of Li2−xMMn3O8 (M=Fe, Co) in the range from 0.1 to 1.6 by employing the galvanostatic intermittent titration technique (GITT). AC impedance studies revealed an electrolyte-electrode charge transfer resistance of 260–290 Θ and an electrode double layer capacity of ∼45–70 µF for an electrode area of 6.7 cm2 at room temperature. The chemical diffusion coefficient of the Al,LiAl negative electrode is about three orders of magnitude higher than that of the positive electrode materials. Accordingly, we believe that the diffusion of Li into and out of the cathode material is the rate determining process.

SrSn1−xFexO3−δ (0≤x≤1) perovskites: a novel mixed oxide ion and electronic conductor

Abstract We report the synthesis and investigation of electrical and magnetic properties of double perovskites of the formula ALaMnBO 6 for A = Ca, Sr, Ba and B = Fe, Ru. Powder X-ray diffraction (XRD) shows formation of cubic/pseudocubic perovskite structure for all the phases, with no obvious long-range ordering of B-site cations. Electron diffraction, however, reveals an ordering of Mn and Ru in ALaMnRuO 6 , showing a doubling of the primitive cubic perovskite cell. While the B = Fe phases are paramagnetic insulators, the B = Ru phases are ferrimagnetic semiconductors. It is likely that in the B = Ru phases, a valence equilibrium exists between Mn III /Ru IV and Mn II /Ru V states that is biased toward the latter.

Effect of B-site substitution of (Li,La)TiO3 perovskites by di-, tri-, tetra- and hexavalent metal ions on the lithium ion conductivity

Abstract The electrical conductivity properties of Fe-substituted SrSnO 3 perovskite-type oxides as a function of temperature and oxygen partial pressure are presented. SrSn 1− x Fe x O 3− δ (0≤ x ≤1) was prepared by conventional solid state reaction in air using SrCO 3 , SnO 2 and FeC 2 O 4 u2008·u20082H 2 O. The total electrical conductivity increases with increasing Fe content. Compounds containing low Fe contents ( x −23 and 0.21 atm with predominant n-type and p-type electronic conduction at low and high oxygen partial pressure, respectively. SrSn 1− x Fe x O 3− δ with high Fe-content ( x >0.5) is found to be a predominant electronic conductor over the entire oxygen partial pressure regime (10 −23 –0.21 atm). The average oxide ion transference number is found to be in the range 0.1–0.5 at 600–850xa0°C for x =0.1–0.2.