Refinement of thermodynamic data for LaMnO3

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Titre du document / Document title

Refinement of thermodynamic data for LaMnO₃

Auteur(s) / Author(s)

JACOB K. T.⁽¹⁾ ; ATTALURI Mrinalini⁽¹⁾ ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

⁽¹⁾Department of Metallurgy, Indian Institute of Science, Bangalore-560012, INDE

Résumé / Abstract

The standard Gibbs energy of formation of LaMnO₃ has been measured in the temperature range from 900 to 1400 K using a solid-state cell incorporating a buffer electrode. The oxygen potential corresponding to the three-phase mixture MnO + La₂O₃ + LaMnO₃ has been measured using pure oxygen gas at 0.1 MPa as the reference electrode, and yttria-stabilized zirconia as the solid electrolyte. The buffer electrode prevented polarization of the three-phase electrode and ensured accurate data. The measured oxygen chemical potential corresponding to the decomposition of LaMnO₃ to MnO, La₂O₃ and O₂ gas is in fair agreement (±6 kJ mol¹) with most data available in the literature and can be represented by the equation, Δμ_O2/J mol^-1 (±520) = -583160 + 170.55 (T/K) Combining this with available information on oxygen potential variation with the non-stoichiometric parameter δ, the standard Gibbs free energy of formation of LaMnO₃ from MnO, La₂O₃ and O₂ was evaluated. The correction for non-stoichiometry was ∼ 1.6(±0.7) kJ mol^-1. The heat capacity of LaMnO₃ has been measured by a differential scanning calorimeter from 400 to 1060 K. Information on low-temperature heat capacity available in the literature was joined smoothly with the high-temperature data to evaluate the standard entropy of LaMnO₃ at 298.15 K as 116.68 J mol-¹ K^-1. The third-law analysis of the Gibbs energy values obtained in this study yields a value of - 155.93 (±0.8) kJ mol^-1 for the standard enthalpy of formation of LaMnO₃ from MnO, La₂O₃ and O₂ at 298.15 K. This value provides a critical test of calorimetric data on enthalpy of formation of LaMnO₃. A consistent set of thermodynamic data for LaMnO₃ is presented from 298.15 to 1400 K based on the results obtained in this study and other supporting information in the literature.

Revue / Journal Title

Journal of material chemistry ISSN 0959-9428

Source / Source

2003, vol. 13, n^o4, pp. 934-942 [9 page(s) (article)] (34 ref.)

Langue / Language

Anglais

Editeur / Publisher

Royal Society of Chemistry, Cambridge, ROYAUME-UNI (1991) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 22603, 35400011115087.0570

Nº notice refdoc (ud4) : 14794879