Abstract
We investigated moderate-temperature oxygen diffusionmechanisms in Sr2ScGaO5 with Brownmillerite structure type. Fromoxygen isotope 18O−16O exchange experiments we determined thatoxygen mobility sets in above 550 °C. Temperature-dependent neutronand X-ray (synchrotron) diffraction experiments allowed us to correlatethe oxygen mobility with a subtle phase transition of the orthorhombicroom-temperature structure with I2mb space group toward Imma, goingalong with a disorder of the (GaO4)∞-tetrahedral chains. From latticedynamical simulations we could clearly evidence that dynamic switchingof the (GaO4)∞-tetrahedral chains from its R to L configuration sets inat 600 °C, thus correlating oxygen diffusion with the dynamic disorder.Oxygen ion diffusion pathways are thus constrained along the onedimensionaloxygen vacancy channels, which is a different diffusionmechanism compared to that of the isostructural CaFeO2.5, wherediffusion of the apical oxygen atoms into the vacant lattice sites are equally involved in the diffusion pathway. The proposedordered room-temperature structure in I2mb is strongly supported by 17O, 45Sc, and 71Ga NMR measurements, which indicatethe presence of crystallographically unique sites and the absence of local disordering effects below the phase transition. Theelectric field gradient tensor components measured at the nuclear sites are found to be in excellent agreement with calculatedvalues using the WIEN2k program. The oxygen site assignment has been independently confirmed by 17O{45Sc} transfer ofadiabatic populations double-resonance experiments.