Thermal and Chemical Expansion of Sr-Doped Lanthanum Cobalt Oxide (La_1-xSr_xCoO_3-δ)

Abstract

The equilibrium thermal expansivity ( T ) and oxygen-vacancy chemical expansivity ( C ) of polycrystalline La 1-x Sr x CoO 3-δ (LSC; x ) 0.2, 0.4, and 0.7) have been measured at 600°C < T < 900°C and 10 -4 atm < P O 2 < 0.21 atm using controlled-atmosphere dilatometry. These measurements show only a moderate dependence of T on temperature, suggesting that increases often observed in the coefficient of thermal expansion when measured at constant P O 2 are primarily thermally induced chemical expansion associated with changes in oxygen stoichiometry. The dependences of T and C on the temperature, oxygen-vacancy concentration, and Sr content (x) were characterized and found to follow a consistent nonlinear trend, which may result from the relaxation of lattice strain with increasing defect concentration. A slowly relaxing secondary expansion effect (and/or expansion hysteresis) was also discovered. Possible causes of this behavior, including phase transition/segregation at high vacancy concentration, are discussed.

Strain-controlled oxygen vacancy formation and ordering in CaMnO3

“…and has an experimental enthalpy of 1.89±0.04 eV in 24 , it is clear that reaction (1) should be accompanied by a considerable volume expansion, which indeed is supported by experiments 25,26 . Since volume increases (decreases) with tensile (compressive) strain, we expect the V O formation energy to be sensitive to strain.…”

Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films

“…Therefore, we further considered the possibility of lattice expansion due to increased vacancy formation as the film deviates from the stoichiometric δ = 0 P-SCO phase in SrCoO 3-δ . [22,28] We compared the unit cell volume of these annealed films to that of the as-grown P-SCO ozone films (see Figure S3 for θ-2θ scans), which have essentially stoichiometric concentrations of oxygen. [23,29,30] As seen in Fig.…”

“…1b, this increased unit cell volume is observed from P-SCO samples prepared by either annealing BM-SCO or P-SCO ozone , indicating a steady-state vacancy concentration attained through, respectively, either the intercalation or deintercalation of oxygen. As the increase in the oxygen 6 vacancies often results in lattice expansion for perovskite-typed complex oxides, we primarily attribute this deviation to the greater oxygen deficiency in the films with tensile strain; [28] otherwise, an unrealistic ν = 0.17 would be required from fully oxygenated films to fit the experimental data. [33] …”

High temperature X-ray diffraction and thermo-gravimetrical analysis of the cubic perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ under different atmospheres

“…The low creep resistance questioning the actual use of BSCF in high temperature gas separation membranes and several attempts to stabilize BSCF by chemical substitution have appeared, both to avoid the formation of the hexagonal polymorph and to increase the creep resistance [22][23] . Chemical expansion [24][25] , particularly for ceria and perovskite materials with transition metals (Co, Fe) on the Bsite is another concern with respect to the mechanical stability of oxygen permeation membranes [26][27][28][29][30][31][32] . The chemical and thermal expansion of BSCF has also been reported by several groups [33][34][35][36][37][38] , showing lower chemical expansion than other similar candidate membrane materials due to smaller changes in oxygen stoichiometry and a generally larger unit cell, which is less sensitive to temperature and stoichiometry changes 38 .…”