Oxide Ion and Proton Conductivity in Highly Oxygen-Deficient Cubic Perovskite SrSc_0.3Zn_0.2Ga_0.5O_2.4

Abstract

A series of Zn-substituted compounds, Sr2Sc1–x Zn x GaO5–0.5x , based on the brownmillerite-type oxide ion conductor Sr2ScGaO5 have been synthesized, and a single-phase region has been identified at 0.4 ≤ x < 0.6. The structure and dynamics of Sr2Sc0.6Zn0.4GaO4.8 were investigated by X-ray and neutron diffraction, neutron total scattering and pair distribution function (PDF) analysis, impedance spectroscopy, and neutron spectroscopy. The material was found to be a highly disordered cubic perovskite with a remarkable level of oxygen deficiency across a large temperature range. These structural properties lead to an increase of oxide ion conductivity of about two orders of magnitude relative to the parent Sr2ScGaO5. The presence of proton conductivity and some water uptake was suggested by the impedance data and corroborated by thermogravimetric analysis (TGA), solid state nuclear magnetic resonance (NMR), variable temperature X-ray diffraction, and neutron spectroscopy. Both proton and oxide ion conductivity produced a measurable quasi-elastic neutron scattering (QENS) signal, and the onset of each dynamic process could be observed by monitoring the temperature dependence of the elastic and inelastic scattering intensities measured in fixed window scans. Neutron total scattering and PDF studies revealed a local structure that is markedly different from the perovskite average structure, and we propose that Sr2Sc0.6Zn0.4GaO4.8 contains a rare one-coordinate or terminal oxygen site.

Structure–property correlation in oxide-ion and proton conductors for clean energy applications: recent experimental and computational advancements

“…The experimental work, which we focus on here, has primarily been done by nuclear magnetic resonance (NMR) and QENS and have focused on the determination of conduction pathways, characteristic timescale and activation energies for the ionic motion. 83,[93][94][95][96][97][98] The computational studies, which encompass both static lattice and molecular dynamics techniques, complemented and assisted in the interpretation of experimental data and, therefore, had a predictive role in the improvement of materials.…”

Understanding the Correlation between Oxide Ion Mobility and Site Distributions in Ba3NbWO8.5

“…The ionic conductors with general formula Ba 3 M 2 O 8.5±δ ( M = Nb, V, Mo, W) have recently attracted attention due to their promising conductivity at temperatures considered “moderate” for applications such as electrolytes in solid-oxide fuel cells (SOFCs). − The best-performing material in this class reported so far, Ba 3 Nb 0.9 V 0.1 MoO 8.5 , has ionic conductivity that reaches 0.01 S/cm at 600 °C . This conductivity compares favorably with that of yttria-stabilized zirconia and the best performers in the scheelite, , apatite , and brownmillerite , structural families; it is very similar to La 2 Mo 2 O 9 , Na 0.5 Bi 0.5 TiO 3 , and melilite-type La 1.54 Sr 0.46 Ga 3 O 7.27 but lower than the best Bi 2 O 3 -based oxide ion conductors . However, it has been demonstrated that Ba 3 M 2 O 8.5±δ materials have the capacity for performance enhancement by compositional tuning …”

Solid oxide proton conductors beyond perovskites

“…Please do not adjust margins Other brownmillerite compounds exhibiting proton conductivity are Ba2InGaO5 and Sr2ScGaO5 129,130 . The ionic conductivity of Ba2InGaO5 is quite modest due to ordering of the In and Ga cations along the stacking axis, which further stabilises the orthorhombic brownmillerite structure 129 .…”

“…The ionic conductivity of Ba2InGaO5 is quite modest due to ordering of the In and Ga cations along the stacking axis, which further stabilises the orthorhombic brownmillerite structure 129 . Sr2ScGaO5 also exhibits a moderate protonic component 130 . However, heavily Zn-doped Sr2ScGaO5 (Sr2Sc1-xZnxGaO5-0.5x, 0.4 ≤ x ≤ 0.6) presents a highly disordered and highly oxygen deficient perovskite structure with a peculiar one-coordinate oxygen site and shows significant proton conductivity, with three orders of magnitude increase in the conductivity in comparison with the parent compound 130 .…”

“…Sr2ScGaO5 also exhibits a moderate protonic component 130 . However, heavily Zn-doped Sr2ScGaO5 (Sr2Sc1-xZnxGaO5-0.5x, 0.4 ≤ x ≤ 0.6) presents a highly disordered and highly oxygen deficient perovskite structure with a peculiar one-coordinate oxygen site and shows significant proton conductivity, with three orders of magnitude increase in the conductivity in comparison with the parent compound 130 . A recent study has demonstrated that the brownmillerite Sr2Co2O5 can absorb one H per formula unit, forming hydronated HSrCoO2.5 (although this phase is stable only up to 160 °C) 131,132 .…”