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  • Author or Editor: S. Bharadwaj x
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Abstract  

La2Mo2O9 (LMO) was synthesized at lower temperature 973 K (LT-phase) by ceramic route. Differential thermal analysis (DTA) scan of LT-phase of LMO showed α→β transition at 843 K during heating and β→α conversion via a metastable γ-phase during cooling. This was also confirmed by thermo-dilatometry and impedance spectroscopy. La2Mo1.95V0.05O9-δ (LMVO), La1.96Sr0.04Mo2O9-δ (LSMO) and La1.96Sr0.04Mo1.95V0.05O9-δ (LSMVO) were prepared in a similar way. These compounds exhibited α→β transition on heating with shift in transition temperature, but the existence of γ-phase during cooling disappeared. Substitution increased the ionic conductivity of α-phase and reduced that of β-phase.

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Abstract  

Thermodynamic stability of CdMoO4 was determined by measuring the vapor pressures of Cd and MoO3 bearing gaseous species. Th vaporization reaction could be described as CdMoO4(s)+MoO2(s) =Cd(g)+2/n(MoO3)n (n=3, 4 and 5). The vapor pressures of the cadmium (p Cd) and trimer (p (MoO3)3) measured in the temperature range 987≤T/K≤1111 could be expressed, respectively, as ln (p Cd/Pa) = –32643.9/T+29.460.08 and ln(p (MoO3)3/Pa) = –32289.6/T+29.280.08. The standard molar Gibbs free energy of formation of CdMoO4(s), derived from the vaporization results could be expressed by the equations: f G CdMoO4 (s) 0= –1002.0+0.267T14.5 kJ mol–1 (987≤T/K≤1033) and f G CdMoO4 (s) 0 = –1101.9+0.363T14.4 kJ mol–1 (1044≤T/K≤1111). The standard enthalpy of formation of CdMoO4(s) was found to be –1015.414.5 kJ mol–1 .

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Abstract  

Sr2CeO4 has been prepared by sol-combustion and co-precipitate routes and the resulting products have been characterized by XRD analysis. The molar enthalpies of solution of Sr2CeO4, Sr(NO3)2(s) and Ce(NO3)36H2O(s) in 0.150 dm3 of (4.41 mol dm3 H2O2+4.23 mol dm-3 of HNO3) solvent as well as the molar enthalpies of solution of Sr2CeO4(s), SrCl2(s) and CeCl3(s) in 0.150 dm3of (1.47 mol dm-3 H2O2+3.05 mol dm-3 of HClO4) solvent have been measured using an isoperibol type calorimeter. From these results and other auxiliary data, the standard molar enthalpy of formation of Sr2CeO4 has been derived to be -2277.33.1 kJ mol-1 at 298.15 K. This is the first reported thermodynamic data on this compound.

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Abstract

In this article, the role of the preparation route and calcinations temperature on the thermal expansion and conductivity of BaCe0.8Y0.2O3−δ (BCY) has been studied. In particular, the samples were synthesized by means of the solid-state reaction and by a sol–gel route. BCY has been suggested as proton conducting electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Proton conductivity strongly depends on the densification of the material as well as the crystal structure, which is generally influenced by the preparation procedure. It was found that a single phase material could be achieved at 1000 °C for the samples prepared through the sol–gel route with ~96% packing density. In case of ceramic route, single phase could be obtained at higher temperatures (1200 °C) and does not lead to good density values. The ceramic synthesis produces BCY material in cubic symmetry where as the gel–citrate complexation route leads to homogenous orthorhombic BCY. The conductivity measurements of sample synthesized by two different routes were investigated by means of impedance spectroscopy and electron microscopy. A comparative study of thermal expansion behavior of BCY synthesized by different route was carried out.

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