Energetics of La1-xAxCrO3-δ perovskites (A = Ca or Sr)

Jihong Cheng, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

A series of perovskites with the general formula La1-xA xCrO3-δ (A = Ca or Sr) have been synthesized in the solid solution range 0.0<x≤0.3 and 0.0≤δ≤0.5x with a variety of heat treatments. High-temperature drop solution calorimetry in molten 2PbO·B2O3 at 1080 K was performed to determine their enthalpies of formation from oxides at room temperature. The enthalpy of oxidation involved in the reaction 2CrCrx + V O.. + 0.5O2(g) = 2CrCr. + OOx is roughly independent of oxygen nonstoichiometry (δ) in each series with a given dopant composition, but varies with composition (x). The values change from -620±260 to -280±80 kJ/mol O2 when x = 0.1-0.3 for Ca-doped samples, and from -440±150 to -290±50 kJ/mol O2 for Sr-doped ones. This dependence of enthalpy of oxidation on composition suggests oxygen vacancies are increasingly short-range ordered in reduced samples. The higher oxidation state of chromium is stabilized by the substitution of alkaline earth ions, but with increasing doping, the enthalpy of formation of the fully oxidized sample in both Ca and Sr-doped systems becomes more endothermic. This destabilization effect is attributed to the large endothermic enthalpy of oxygen vacancy formation (395±30 kJ/mol of VO..) for the reaction A Ax + OOx = A′La + 0.5VO.. + 0.5O2(A = Ca or Sr) that over-rides the exothermic enthalpies of oxidation. At a given composition, Sr-doped LaCrO 3 is more stable than its Ca-doped counterpart, which is consistent with basicity arguments.

Original languageEnglish (US)
Pages (from-to)234-244
Number of pages11
JournalJournal of Solid State Chemistry
Volume178
Issue number1
DOIs
StatePublished - Jan 2005
Externally publishedYes

Keywords

  • Doped lanthanum chromite
  • Enthalpy of formation
  • Enthalpy of oxidation
  • Interconnect
  • Oxygen vacancies
  • Perovskites
  • Solid oxide fuel cells
  • Thermodynamics

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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