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2024
ACL
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H.Bazzaoui, M.Gao, O.Hernandez, S.Chenu, L.He, C.Genevois, E.Veron, L.Del Campo, M.Allix, G.Darling, M.S.Dyer, M.J.Pitcher, 'La Substitution into the Melilite Derivative Ca5Ga6O14: Prediction, Synthesis and Ionic Conductivity', Inorg. Chem. 63 18902 (2024) doi:10.1021/acs.inorgchem.4c03172
Melilite-type gallates of general formula RE1+xAE1−xGa3O7+x/2 are of interest for their ability to host mobile interstitial
oxide ions in [Ga3O7+x] layers. The crystal structure of Ca5Ga6O14 is closely related to melilite, with [Ga3O7] layers stacked in a
more complex way to accommodate an additional 0.5 interlayer cations per formula unit, suggesting the potential for similar oxide
ion conduction behavior. We used a computational approach to identify the most promising routes to interstitial oxide incorporation
into Ca5Ga6O14, leading to an experimental investigation of the system Ca5−xLaxGa6O14+x/2. Single-phase materials were obtained in
the range 0 ≤ x ≤ 0.25 by solid state reactions, producing an ∼40× increase in ionic conductivity at 800 °C. This limited
compositional range presents a challenge for characterization of the charge-compensating defects. The La substituents were observed
directly by X-ray diffraction and STEM−EDX, and a combination of different structural characterization techniques and DFT
calculations indicated the presence of interstitial oxide ions indirectly, explaining the conductivity response. As higher carrier
concentrations (x > 0.25) are apparently inaccessible in this system, we conclude that its potential as a useful oxide ion conductor is
more limited than that of established melilite materials such as La1+xCa1−xGa3O7+x/2.
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