Dielectric and ac impedance studies of nanostructured CaCu3Ti3.90Ce0.10O12 electro-ceramic synthesized by citrate-gel route

Effect of doping at Ti⁴⁺ site by Ce³⁺ has been examined in CaCu₃Ti_3.90Ce_0.10O₁₂ synthesized by citrate-gel route. DTA/TG analysis of dry powder gives pre-information about formation of final product around 850 °C. X ray diffraction analysis confirmed the formation of CaCu₃Ti_3.90Ce_0.10O₁₂ phase of the ceramic sintered at 950 °C for 12 h. Microstructure has been studied using scanning electron microscopy and confirmed the average grain size found in nano range 200–400 nm in system CaCu₃Ti_3.90Ce_0.10O₁₂.The nature of relaxation behavior of ceramic was also rationalized by using the impedance and modulus spectroscopy. The bulk conductivity indicates an Arrhenius-type thermally activated process. The ac conductivity spectrum obeyed the Jonscher power law. The complex impedance diagrams of the ceramic exhibited a significant contribution from the grains, grain boundaries and electrode. The activation energies calculated from the grain-boundary relaxation time constant was found to be 0.49 eV which confirmed the Maxwell–Wagner type of relaxation present in the ceramic.     

The satellite-shaped Co-15 Polyoxotungstate, [Co6(H2O)30{Co9Cl2(OH)3(H2O)9(beta-SiW8O31)3}]5-

The 15-cobalt-substituted polyoxotungstate [Co(6)(H(2)O)(30){Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}](5-) (1) has been characterized by single-crystal XRD, elemental analysis, IR, electrochemistry, magnetic measurements, and EPR. Single-crystal X-ray analysis was carried out on Na(5)[Co(6)(H(2)O)(30){Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}].37H(2)O, which crystallizes in the hexagonal system, space group P6(3)/m, with a = 19.8754(17) A, b = 19.8754(17) A, c = 22.344(4) A, alpha= 90 degrees, beta = 90 degrees, gamma = 120 degrees, and Z = 2. The trimeric polyanion 1 has a core of nine Co(II) ions encapsulated by three unprecedented (beta-SiW(8)O(31)) fragments and two Cl(-) ligands. This central assembly {Co(9)Cl(2)(OH)(3)(H(2)O)(9)(beta-SiW(8)O(31))(3)}(17-) is surrounded by six antenna-like Co(II)(H(2)O)(5) groups resulting in the satellite-like structure 1. Synthesis of 1 is accomplished in a simple one-pot procedure by interaction of Co(II) ions with [gamma-SiW(10)O(36)](8-) in aqueous, acidic NaCl medium (pH 5.4). Polyanion 1 was studied by cyclic voltammetry as a function of pH. The current intensity of its Co(II) centers was compared with that of free Co(II) in solution. Our results suggest that 1 keeps its integrity in solution. Magnetic susceptibility results show the presence of both antiferro- and ferromagnetic coupling within the (Co(II))(9) core. A fully anisotropic Ising model has been employed to describe the exchange-coupling and yields g = 2.42 +/- 0.01, J(1) = 17.0 +/- 1.5 cm(-1), and J(2) = -13 +/- 1 cm(-(1). Variable frequency EPR studies reveal an anisotropic Kramer's doublet.     

Fly‐Ash‐Supported Synthesis of 2‐Mercaptobenzothiazole Derivatives under Microwave Irradiation

Microwave‐assisted, solvent‐free alkylation and acylation of 2‐mercaptobenzothiazole has been attempted using silica gel, alumina, and a new solid support, fly ash. Fly ash, a waste generated at thermal power stations, could be used as solid support just as efficiently as commercial supports. The additional features of methodology include a much faster reaction, easy workup, higher yields, higher purity of the products, and an ecofriendly approach.     

Studies of Nucleophilic Substitution Reactions of p‐Nitrophenyl Acetate with Some Dihydroxamate Ions in Cationic Micellar Media

Pseudo‐first‐order rate constants have been determined for the nucleophilic substitution reactions of p‐nitrophenyl acetate with oxalo, malono, and succinodihydroxamate ions (^?ONHC(O)(CH₂)_nC(O)NHO^?) in phosphate buffer (pH=7.9) at 27°C. The rate data of the reaction revealed that the nucleophilic reactivity sequence of these hydroxamate ions is generally ODHA>MDHA>SDHA. The k_obs value increases upon addition of cationic surfactants to the reaction medium which is typical behavior of micelle‐assisted bimolecular reactions. The pseudo‐phase ion exchange model has been successfully applied to determine binding constant.     

Physico-Chemical Characterization of Binary and Ternary Mixtures of Imidazolium Based Cation and Common Anion Ionic Liquids with Lactams

Journal of Solution Chemistry - Excess molar volumes, $$V_{{}}^{{\text{E}}}$$ , excess isentropic compressibilities, $$\kappa_{{\text{S}}}^{{\text{E}}}$$ of binary 1-butyl-2,3-dimethylimidazolium...     

Excess heat capacities and excess molar enthalpies of the mixtures containing tetrahydropyran,piperidine and cyclic alkanones

Journal of Thermal Analysis and Calorimetry - In the present study, molar heat capacities, $$\left( {C_{\text{P}}^{{}} } \right)_{123}$$ , at T/K = 293.15–308.15 K...     

Spectrophotometric Label-Free Determination of Lead Using Thiol-Functionalized Gold Nanoparticles

A method for the determination of lead is described using thiol-functionalized gold nanoparticle. The detection method is based on the prevention of thiol-induced aggregation of gold nanoparticles by lead. Among six thiols, e.g., 4-mercapto-1-butanol, meso-2, 3-dimercaptosuccinic acid, mercaptosuccinic acid, 6-mercapto-1-hexanol, 4-(methylthio)-1-butanol, 1-propanethiol, four (4-mercapto-1-butanol, 6-mercapto-1-hexanol, 4-(methylthio)-1-butanol and 1-propanethiol) induced the aggregation of the gold nanoparticles which was measured by the change in absorbance at 520 and 650?nm. Prior incubation of the gold nanoparticles with lead decreased the 4-(methylthio)-1-butanol-induced aggregation of gold nanoparticles in a dose-dependent manner. A linear inverse relationship between the logarithmic concentration of lead and the ratio of absorbance at 650 to 520 was noted. The method has a dynamic range from 10?nM to 100?µM. However, metals such as mercury and chromium were more effective in comparison with lead in preventing the 4-methylthio-1-butanol-induced aggregation of gold nanoparticles. The method can be used for assessing the heavy metal load in water samples.     

“Metal-free” synthesis of 1,2,3-triazoles via tandem azidation,intramolecular [3+2]-cycloaddition and aromatization of ethyl acrylate derivatives

An efficient “one-pot” method for the synthesis of substituted 1,2,3-triazole derivatives in excellent yields as single regioisomer is reported. The key transformation involves an atom-efficient tandem azidation, intramolecular [3+2]-cycloaddition and aromatization of acrylate derivatives on treatment with NaN₃ in DMF under mild conditions.     

Thermodynamic Properties of Ternary Ionic Liquid Mixture Containing a Common Ion: Excess Molar Volumes,Excess Isentropic Compressibilities,Excess Molar Enthalpies and Excess Heat Capacities

In the present investigations, the excess molar volumes, \( V_{ijk}^{\text{E}} \), excess isentropic compressibilities, \( \left( {\kappa_{S}^{\text{E}} } \right)_{ijk} \), and excess heat capacities, \( \left( {C_{p}^{\text{E}} } \right)_{ijk} \), for ternary 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (i) + 1-butyl-3-methylimidazolium tetrafluoroborate (j) + 1-ethyl-3-methylimidazolium tetrafluoroborate (k) mixture at (293.15, 298.15, 303.15 and 308.15) K and excess molar enthalpies, \( \left( {H^{\text{E}} } \right)_{ijk} \), of the same mixture at 298.15 K have been determined over entire composition range of x _i and x _j . Satisfactorily corrections for the excess properties \( V_{ijk}^{\text{E}} \), \( \left( {\kappa_{S}^{\text{E}} } \right)_{ijk} \), \( \left( {H^{\text{E}} } \right)_{ijk} \) and \( \left( {C_{p}^{\text{E}} } \right)_{ijk} \) have been obtained by fitting with the Redlich–Kister equation, and ternary adjustable parameters along with standard errors have also been estimated. The \( V_{ijk}^{\text{E}} \), \( \left( {\kappa_{S}^{\text{E}} } \right)_{ijk} \), \( \left( {H^{\text{E}} } \right)_{ijk} \) and \( \left( {C_{p}^{\text{E}} } \right)_{ijk} \) data have been further analyzed in terms of Graph Theory that deals with the topology of the molecules. It has also been observed that Graph Theory describes well \( V_{ijk}^{\text{E}} \), \( \left( {\kappa_{S}^{\text{E}} } \right)_{ijk} \), \( \left( {H^{\text{E}} } \right)_{ijk} \) and \( \left( {C_{p}^{\text{E}} } \right)_{ijk} \) values of the ternary mixture comprised of ionic liquids.