Local Structure in Disordered Melilite Revealed by Ultrahigh Field 71Ga and 139La Solid‐State Nuclear Magnetic Resonance Spectroscopy

⁷¹Ga solid-state NMR spectroscopy at ultrahigh external magnetic field and under fast magic angle spinning rates transforms the spectral resolution and clearly captures Ga sites in four- and five-fold coordination environments. GaO₅ structural units form to accommodate the interstitial oxide ions responsible for the excellent ionic transport properties in La_1.54Sr_0.46Ga₃O_7.27.

Abstract

Multinuclear Nuclear Magnetic Resonance (NMR) spectroscopy of quadrupolar nuclei at ultrahigh magnetic field provides compelling insight into the short-range structure in a family of fast oxide ion electrolytes with La_1+x Sr_1-x Ga₃O_7+0.5x melilite structure. The striking resolution enhancement in the solid-state ⁷¹Ga NMR spectra measured with the world's unique series connected hybrid magnet operating at 35.2 T distinctly resolves Ga sites in four- and five-fold coordination environments. Detection of five-coordinate Ga centers in the site-disordered La_1.54Sr_0.46Ga₃O_7.27 melilite is critical given that the GaO₅ unit accommodates interstitial oxide ions and provides excellent transport properties. This work highlights the importance of ultrahigh magnetic fields for the detection of otherwise broad spectral features in systems containing quadrupolar nuclei and the potential of ensemble-based computational approaches for the interpretation of NMR data acquired for site-disordered materials.

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