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Monoclinic natrium superionic conductors (NASICON; Na3Zr2Si2PO12) are well‐known Na‐ion solid electrolytes which have been studied for 40 years. However, due to the low symmetry of the crystal structure, identifying the migration channels of monoclinic NASICON accurately still remains unsolved. Here, a cross‐verified study of Na+ diffusion pathways in monoclinic NASICON by integrating geometric analysis of channels and bottlenecks, bond‐valence energy landscapes analysis, and ab initio molecular dynamics simulations is presented. The diffusion limiting bottlenecks, the anisotropy of conductivity, and the time and temperature dependence of Na+ distribution over the channels are characterized and strategies for improving both bulk and total conductivity of monoclinic NASICON‐type solid electrolytes are proposed. This set of hierarchical ion‐transport algorithms not only shows the efficiency and practicality in revealing the ion transport behavior in monoclinic NASICON‐type materials but also provides guidelines for optimizing their conductive properties that can be readily extended to other solid electrolytes. [ABSTRACT FROM AUTHOR]

In principle, thermoelectric materials with superior performance require high lattice symmetry and heavy components integrated in semiconductors. Cu 6 WSnSe 8 , isostructural to kiddcreekite Cu 6 WSnS 8 , possesses the characteristics for being a promising thermoelectric material, including narrow band-gap, high crystal symmetry, heavy constituent elements, and complex crystal structure. In this work, the thermoelectric transport properties of pristine and copper-deficient Cu 6 WSnSe 8 were investigated. The extremely low hole mobility restricts Cu 6 WSnSe 8 as an excellent thermoelectric parent despite the fact that Cu-deficiency can increase the electrical conductivity and boost the power factor of Cu 5.94 WSnSe 8 by four times than that of pristine Cu 6 WSnSe 8. Combined with density functional theory calculations and X-ray photoelectron spectra analysis, we conclude that the extremely low hole mobility derives from the charge localization around W cations. Due to charge transfer and redistribution, the high valence state W6+ seizes electrons from Se2−, and thus localizing carriers. [Display omitted] • Kiddcreekite-type Cu 6 WSnSe 8 has been synthesized by mild solid-state reaction method at 773 K. • Cu-deficiency can significantly increase the electrical conductivity and boost the power factor. • The presence of W blocks the hole transport and results in ultralow hole mobility. [ABSTRACT FROM AUTHOR]