Morgan Emily E, Evans Hayden A, Pilar Kartik, Brown Craig M, Clément Raphaële J, Maezono Ryo, Seshadri Ram, Monserrat Bartomeu, Cheetham Anthony K
Materials Department and Materials Research Laboratory, University of California, Santa Barbara, California 93106, United States.
NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20878, United States.
Chem Mater. 2022 May 10;34(9):4029-4038. doi: 10.1021/acs.chemmater.2c00212. Epub 2022 Apr 28.
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(PO), and obtain detailed insights into such behavior via variable-temperature neutron diffraction and Na and 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.
钠超离子导体（NASICON）化合物构成了一类丰富且化学性质高度可调控的晶体材料家族，这类材料受到广泛关注，因为它们包含具有高离子电导率、低热膨胀率和氧化还原可调性的范例。这使得它们成为从固态电池到核废料储存材料等各种应用的合适候选材料。理解这些性质的关键，包括有效阳离子传输的起源以及低的、各向异性（有时为负）的热膨胀，在于与晶体结构特定细节相关的晶格动力学。在这里，我们仔细研究了典型的NASICON化合物NaZr(PO)，并通过变温中子衍射以及Na和P的固态核磁共振研究，结合基于密度泛函理论的核磁共振参数综合计算，获得了对此类行为的详细见解。温度依赖的核磁共振研究揭示了化学位移和四极耦合常数中一些令人惊讶的趋势，这些趋势除非明确考虑晶体的基础振动模式，否则计算无法捕捉到。此外，我们动力学模拟中钠、锆和氧原子的轨迹与通过中子衍射在较高温度下获得的各向异性热参数显示出良好的定性一致性。本文所展示的工作拓宽了核磁共振晶体学的应用范围，将热效应纳入其中，作为探测功能材料中有趣晶格动力学的独特手段。
