Thermodynamic properties of nano- and micro- structured perovskite-type compounds

Speranta Tanasescu ,  Cornelia Marinescu ,  Florentina Maxim 

Romanian Academy, Institute of Physical Chemistry "I.G.Murgulescu" (IPC), Splaiul Independentei 202, Bucharest 77208, Romania

Abstract

The acceptor doped micro- and nanostructured lanthanum perovskites form an important and interesting object of study owing to their technologically useful electric, magnetic and catalytic properties. Besides the determination of their electrical and structural characteristics, the knowledge of the thermodynamics of the new materials is very important in order to evaluate and optimize the properties for utilization in different applications.

In the present paper the thermodynamic properties of some doped nano- and micro- structured lanthanum manganites of general formula La1-xMxMn1-yMeyO3 (where M=Ca; Me=Al; 0.3<x<1; y=0;0.05) have been studied within the temperature range of 1073-1273 K and in reducing atmosphere (10-5 Pa). The relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressures of oxygen have been obtained by using a solid electrolyte galvanic cells method. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with EMF measurements.

The research was focused on emphasising the modifications in the thermodynamic properties connected with the nanocrystalline state. The results obtained for the nanocrystalline ceramics are discussed being related with the significant changes in the overall defect concentrations.

Presentation: oral at E-MRS Fall Meeting 2003, Symposium F, by Speranta Tanasescu
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-27 15:14
Revised:   2009-06-08 12:55
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