DFT-based 11B solid state NMR calculations for guiding fine local structure identification and phase-property modulation in ZnxY1-xBO3-0.5x borate oxide ion conductors

Abstract

Solid-state nuclear magnetic resonance (NMR) spectroscopy serves as a powerful technique for probing local structures. However, the interpretation of NMR signals mainly based on empirical knowledge could lead to unprecise local structural determinations. To address this, density functional theory (DFT)-based theoretical NMR calculations, aided by the experimental three-dimensional continuous rotation electronic diffraction (3D cRED) technique, were performed for ZnxY1-xBO3-0.5x borate oxide ion conductors and provided a fine local structure identification for the experimental 11B NMR spectra of ZnxY1-xBO3-0.5x, acquiring rich information on the multiple experimental 11B NMR signals to the complex boron oxide anions associated with bridging oxygen vacancies and the coexistence of the monoclinic phase (C2/c), hexagonal (P63/m), and trigonal (R32) phases in ZnxY1-xBO3-0.5x. Thanks to the advantages of solid-state NMR in identifying close phases exceeding X-ray/neutron diffraction technique, and the advanced 3D cRED technique that allows for rapid phase identification and structure determination, we provide a fine local structure identification and a more inclusive insight into the coexistence of multiple phases in borate with the same composition, and more importantly, in turn provides guidance for phase and property modulation. The phase modulation in ZnxY1-xBO3-0.5x was carried out in thermodynamic and kinetic, respectively, and eventually realized the modulation of the local structures and the resultant oxide ion conductivity of ZnxY1-xBO3-0.5x. This work provides a theoretical and experimental platform to access the flexible structural assignment of boron oxide anions and therefore offer new guidance and insights into the defect structures and the phase-property modulation of inorganic solid functional materials not only in the borate oxide ion conductors.