Effects of A-site composition and oxygen nonstoichiometry on the thermodynamic stability of compounds in the Ba–Sr–Co–Fe–O system

Journal Article · Mon Apr 15 04:00:00 EDT 2013 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2013.01.030· OSTI ID:22304576

Tanasescu, Speranta ^[1]; Yáng, Zhèn ^[2]; Martynczuk, Julia ^[2]; Varazashvili, Vera ^[3]; Maxim, Florentina ^[1]; Teodorescu, Florina ^[1]; Botea, Alina ^[1]; Totir, Nicolae ^[1]; others, and

---

1. “Ilie Murgulescu” Institute of Physical Chemistry of Romanian Academy, Department of Chemical Thermodynamics, Splaiul Independentei 202, PO Box 12-194, 060021 Bucharest (Romania)
2. ETH Zurich, Nonmetallic Inorganic Materials, Department of Materials, Wolfgang-Pauli-Str. 10, CH-8093 Zurich (Switzerland)
3. Ivan Javakhishvili Tbilisi State University, 11, Mindeli str., Tbilisi, 380086, Georgia (United States)

The thermodynamic stability of the perovskite-type oxides in the Ba{sub x}Sr{sub 1−x}Co{sub 0.8}Fe{sub 0.2}O{sub 3−δ} (BSCF) system was investigated with varying Ba:Sr ratios (x=0.2, 0.4, 0.5, 0.6, 0.8) and correlated with the charge compensation mechanism and the change in the oxygen stoichiometry of the materials. Thermodynamic properties represented by 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 in the temperature range of 823–1273 K using solid electrolyte electrochemical cells (EMF) method. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using a coulometric titration technique coupled with EMF measurements. The temperature dependence of enthalpy increment (H{sub T}−H{sub 298}) in the temperature range of 700–900 K was measured by drop calorimetry. The energetic parameters allow for the correlation of the structural and electrical stability with the defect structures. - Graphical abstract: Partial molar energy of oxygen dissolution (ΔG{sup ¯}{sub O{sub 2}}) (EMF measurements) and enthalpy increment (H{sub T}−H{sub 298}) (drop calorimetry data) of perovskite materials with the composition Ba{sub x}Sr{sub 1−x}Co{sub 0.8}Fe{sub 0.2}O{sub 3−δ} as a function of temperature and Barium content. Highlights: ► We report relevant data for thermodynamic stability of Ba{sub x}Sr{sub 1−x}Co{sub 1−y}Fe{sub y}O{sub 3−δ} compounds. ► Temperature of structural transformations is evidenced as a function of Ba content. ► Correlation between thermodynamic, electrical and structural data is investigated. ► The results are discussed based on the properties-defect structure relationship.

• OSTI ID: 22304576
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Vol. 200; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
BARIUM
CALORIMETRY
DISSOLUTION
ELECTROMOTIVE FORCE
ENTHALPY
ENTROPY
FREE ENERGY
OXIDES
OXYGEN
PARTIAL PRESSURE
PEROVSKITE
SOLID ELECTROLYTES
SOLID OXIDE FUEL CELLS
TEMPERATURE DEPENDENCE
TITRATION