Lattice Dynamics in the NASICON NaZr₂(PO₄)₃ Solid Electrolyte from Temperature-Dependent Neutron Diffraction, NMR, and Ab Initio Computational Studies

Abstract

Natrium super ionic conductor (NASICON) compounds form a rich and highly chemically tunable family of crystalline materials that are of widespread interest because they include exemplars with high ionic conductivity, low thermal expansion, and redox tunability. This makes them suitable candidates for applications ranging from solid-state batteries to nuclear waste storage materials. The key to an understanding of these properties, including the origins of effective cation transport and low, anisotropic (and sometimes negative) thermal expansion, lies in the lattice dynamics associated with specific details of the crystal structure. Here we closely examine the prototypical NASICON compound, NaZr 2 (PO 4 ) 3 , and obtain detailed insights into such behavior via variable-temperature neutron diffraction and 23 Na and 31 P solid-state NMR studies, coupled with comprehensive density functional theory-based calculations of NMR parameters. Temperature-dependent NMR studies yield some surprising trends in the chemical shifts and the quadrupolar coupling constants that are not captured by computation unless the underlying vibrational modes of the crystal are explicitly taken into account. Furthermore, the trajectories of the sodium, zirconium, and oxygen atoms in our dynamical simulations show good qualitative agreement with the anisotropic thermal parameters obtained at higher temperatures by neutron diffraction. The work presented here widens the utility of NMR crystallography to include thermal effects as a unique probe of interesting lattice dynamics in functional materials.

Crystal structure solution and high-temperature thermal expansion in NaZr2(PO4)3-type materials

“…A combination of both X-ray pair distribution function (XPDF) and X-ray absorption fine structure (XAFS) led to a study of the changes in a network structure (Cao et al, 2003;Bridges et al, 2014) that were caused by low-energy vibrational modes. A recent study that combined temperaturedependent solid-state NMR, neutron diffraction, and computation DFT (Morgan et al, 2022) examined Na l+x Zr 2 Si x -P 3-x O 12 . It could be useful to apply these techniques to understanding the differences in a-axis positive and negative expansions in the CaZP-SrZP system.…”

Research progress of all-solid-state lithium–sulfur batteries with sulfide solid electrolytes: materials, interfaces, challenges, and prospects

“…Oxide SEs include various types, such as garnet, 56 NASICON, 57 LiPON, 58 LISICON 59 and perovskite. 60 Compared with SPEs, oxide SEs have higher ionic conductivity and Li + transference numbers.…”