Intricate Short-Range Ordering and Strongly Anisotropic Transport Properties of Li1–xSn2+xAs2

A new ternary compound, Li1–xSn2+xAs2, 0.2 x R3̅m space group (No. 166) with Sn–As layers separated by layers of jointly occupied Li/Sn atoms. The Sn–As layers are comprised of Sn3As3 puckered hexagons in a chair conformation that share all edges. Li/Sn atoms in the interlayer space are surrounded by a regular As6 octahedron. Thorough investigation by synchrotron X-ray and neutron powder diffraction indicate no long-range Li/Sn ordering. In contrast, the local Li/Sn ordering was revealed by synergistic investigations via solid-state 6,7Li NMR spectroscopy, HRTEM, STEM, and neutron and X-ray pair distribution function analyses. Due to their different chemical natures, Li and Sn atoms tend to segregate into Li-rich and Sn-rich regions, creating substantial inhomogeneity on the nanoscale. The inhomogeneous local structure has a high impact on the physical properties of the synthesized compounds: the local Li/Sn ordering and multiple nanoscale interfaces result in unexpectedly low thermal conductivity and highly anisotropic resistivity in Li1–xSn2+xAs2.