Lattice dynamics to trigger low temperature oxygen mobility in solid oxide ion conductors.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Inorganic Chemistry

Background:

• Strontium iron oxide (SrFeO(2.5)) and strontium cobalt oxide (SrCoO(2.5)) reversibly intercalate oxygen at room temperature, forming cubic perovskites.
• Calcium iron oxide (CaFeO(2.5)) requires extreme conditions for oxidation, highlighting a significant difference in oxygen mobility.

Purpose of the Study:

• To elucidate the reasons behind the distinct low-temperature oxygen mobility in SrFeO(2.5) compared to CaFeO(2.5).
• To investigate the role of lattice dynamics in facilitating oxygen diffusion in oxygen-deficient perovskites.

Main Methods:

• Temperature-dependent oxygen isotope exchange experiments using (18)O/(16)O.
• Inelastic neutron scattering (INS) studies.
• Ab initio (Density Functional Theory) molecular dynamical calculations.

Main Results:

• Free oxygen mobility was confirmed in SrFeO(x) below 600 K.
• Low-temperature oxygen mobility is linked to specific, low-energy lattice modes.
• Enhanced, phonon-assisted oxygen diffusion in SrFeO(3-x) is attributed to weakened Fe-O-Fe bonds of apical oxygen atoms.

Conclusions:

• Lattice dynamics significantly impact oxygen mobility in oxygen-deficient perovskites, particularly those with brownmillerite structures.
• Dynamically triggered phenomena, like phonon-assisted diffusion, enable facile oxide ion migration.
• These findings provide new concepts for designing and tailoring low-temperature oxygen ion conductors.