Ab Initio Investigation of Migration Mechanisms in La Apatites

Schultze, Tim; Arnold, John P.; Grieshammer, Steffen

doi:10.1021/acsaem.9b00226

Journal Article

FZJ-2019-06487

Ab Initio Investigation of Migration Mechanisms in La Apatites

Schultze, T.FZJ* ; Arnold, J. P.RWTH* ; Grieshammer, S. (Corresponding author)FZJ*

2019
ACS Publications Washington, DC

ACS applied energy materials 2(7), 4708 - 4717 (2019) [10.1021/acsaem.9b00226]

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Please use a persistent id in citations: http://hdl.handle.net/2128/24289 doi:10.1021/acsaem.9b00226

Abstract: Lanthanum-apatite structures are promising materials for solid-state electrolytes, exceeding the oxygen ion conductivity of yttria-stabilized zirconia at intermediate temperatures. In recent years, several experimental contributions on La-apatites have been published, however, with divergent results. A comprehensive description of migration in dependence on composition is required to further optimize these materials and to predict the properties of similar structures. In this work, the compositions La9.33Si6O26, La10Si6O27 and La8B2Si6O26 (B = Mg, Ca, Sr, Ba) are investigated by means of density functional theory. Different migration paths are considered, and migration energies are obtained via climbing-image nudged elastic band calculations for both the vacancy and interstitialcy mechanism. Migration inside the highly conductive La-tunnel and in the ab plane between La-tunnels is taken into consideration. Among all investigated B doped compositions, La8Sr2Si6O26 shows a minimum in migration energy along the c-axis for the vacancy and interstitialcy mechanism in agreement with the experimental data. Furthermore, the results indicate that the type of migration mechanism depends on the synthesized composition, while the thermal excitation of defects plays a minor role. From our results, we infer that the activation energy of oxygen ion conductivity is mainly governed by the migration in the ab plane.

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