Cation Distribution and Anion Transport in the La3Ga5-xGe1+xO14+0.5x Langasite Structure.



Corti, Lucia, Hung, Ivan, Venkatesh, Amrit, Gan, Zhehong, Claridge, John B, Rosseinsky, Matthew J and Blanc, Frédéric
(2024) Cation Distribution and Anion Transport in the La3Ga5-xGe1+xO14+0.5x Langasite Structure. Journal of the American Chemical Society, 146 (20). pp. 14022-14035.

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Abstract

Exploration of compositional disorder using conventional diffraction-based techniques is challenging for systems containing isoelectronic ions possessing similar coherent neutron scattering lengths. Here, we show that a multinuclear solid-state Nuclear Magnetic Resonance (NMR) approach provides compelling insight into the Ga<sup>3+</sup>/Ge<sup>4+</sup> cation distribution and oxygen anion transport in a family of solid electrolytes with langasite structure and La<sub>3</sub>Ga<sub>5-<i>x</i></sub>Ge<sub>1+<i>x</i></sub>O<sub>14+0.5<i>x</i></sub> composition. Ultrahigh field <sup>71</sup>Ga Magic Angle Spinning (MAS) NMR experiments acquired at 35.2 T offer striking resolution enhancement, thereby enabling clear detection of Ga sites in different coordination environments. Three-connected GaO<sub>4</sub>, four-connected GaO<sub>4</sub> and GaO<sub>6</sub> polyhedra are probed for the parent La<sub>3</sub>Ga<sub>5</sub>GeO<sub>14</sub> structure, while one additional spectral feature corresponding to the key (Ga,Ge)<sub>2</sub>O<sub>8</sub> structural unit which forms to accommodate the interstitial oxide ions is detected for the Ge<sup>4+</sup>-doped La<sub>3</sub>Ga<sub>3.5</sub>Ge<sub>2.5</sub>O<sub>14.75</sub> phase. The complex spectral line shapes observed in the MAS NMR spectra are reproduced very accurately by the NMR parameters computed for a symmetry-adapted configurational ensemble that comprehensively models site disorder. This approach further reveals a Ga<sup>3+</sup>/Ge<sup>4+</sup> distribution across all Ga/Ge sites that is controlled by a kinetically governed cation diffusion process. Variable temperature <sup>17</sup>O MAS NMR experiments up to 700 °C importantly indicate that the presence of interstitial oxide ions triggers chemical exchange between all oxygen sites, thereby enabling atomic-scale understanding of the anion diffusion mechanism underpinning the transport properties of these materials.

Item Type: Article
Uncontrolled Keywords: 3402 Inorganic Chemistry, 34 Chemical Sciences
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 09 May 2024 07:16
Last Modified: 20 Sep 2024 09:55
DOI: 10.1021/jacs.4c02324
Open Access URL: https://pubs.acs.org/doi/full/10.1021/jacs.4c02324
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3180843