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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on KTl(CN)4 by Materials Project

KTl(CN)4 crystallizes in the tetragonal I4_1/a space group. The structure is three-dimensional and consists of two KTl(CN)4 frameworks. K1+ is bonded in a tetrahedral geometry to four equivalent N3- atoms. All K–N bond lengths are 2.90 Å. Tl1+ is bonded in a tetrahedral geometry to four equivalent C+2.50+ atoms. All Tl–C bond lengths are 2.21 Å. C+2.50+ is bonded in a linear geometry to one Tl1+ and one N3- atom. The C–N bond length is 1.17 Å. N3- is bonded in a distorted bent 120 degrees geometry to one K1+ and one C+2.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KTl by Materials Project

KTl crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two KTl sheets oriented in the (0, 0, 1) direction. K is bonded in a 6-coordinate geometry to six equivalent Tl atoms. All K–Tl bond lengths are 3.76 Å. Tl is bonded in a 9-coordinate geometry to six equivalent K and three equivalent Tl atoms. All Tl–Tl bond lengths are 3.13 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KTl by Materials Project

KTl crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. there are three inequivalent K sites. In the first K site, K is bonded in a 4-coordinate geometry to four equivalent Tl atoms. There are two shorter (3.75 Å) and two longer (3.81 Å) K–Tl bond lengths. In the second K site, K is bonded in a 6-coordinate geometry to six Tl atoms. There are a spread of K–Tl bond distances ranging from 3.71–3.93 Å. In the third K site, K is bonded in a 6-coordinate geometry to six Tl atoms. There are a spread of K–Tl bond distances ranging from 3.70–4.06 Å. There are two inequivalent Tl sites. In the first Tl site, Tl is bonded in a 8-coordinate geometry to four K and four equivalent Tl atoms. There are two shorter (3.15 Å) and two longer (3.17 Å) Tl–Tl bond lengths. In the second Tl site, Tl is bonded in a 8-coordinate geometry to six K and two equivalent Tl atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KTl(CoSe)4 by Materials Project

KTl(CoSe)4 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. K1+ is bonded in a body-centered cubic geometry to eight equivalent Se2- atoms. All K–Se bond lengths are 3.41 Å. Co+1.50+ is bonded to four Se2- atoms to form a mixture of edge and corner-sharing CoSe4 tetrahedra. There are two shorter (2.34 Å) and two longer (2.35 Å) Co–Se bond lengths. Tl1+ is bonded in a body-centered cubic geometry to eight equivalent Se2- atoms. All Tl–Se bond lengths are 3.42 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to four equivalent Co+1.50+ and four equivalent Tl1+ atoms. In the second Se2- site, Se2- is bonded in a 8-coordinate geometry to four equivalent K1+ and four equivalent Co+1.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Heterostructured Lepidocrocite Titanate-Carbon Nanosheets for Electrochemical Applications

Lepidocrocite-type titanates that reversibly intercalate sodium ions at low potentials (~0.6 V vs Na/Na + ) are promising anode candidates for sodium-ion batteries. However, large amounts of carbon additives are often used to improve their electrical conductivity and overcome poor cycling performance in the electrode composites. To ameliorate electronic transport issues of lepidocrocite titanate (K 0.8 Ti 1.73 Li 0.27 O 4 , KTL) in sodium-ion batteries, we have designed and synthesized heterostructures of exfoliated lepidocrocite-type titanium oxide (LTO) nanosheets with alternating carbon layers via a solution-based self-assembly approach. Positively charged dopamine (Dopa) was used as the carbon precursor and intercalated between negatively charged exfoliated titania nanosheets through electrostatic interaction. Dopa-intercalated LTO was then annealed under argon to form conductive carbon layers between titania sheets. The carbon content in the heterostructures was controlled by modifying the self-assembly conditions (i.e., pH, stirring duration, and Dopa-to-LTO ratio). Electrodes were prepared using carbonized heterostructures (LTO-C) without adding more carbon to the composites and tested in sodium half-cell configurations. Further, higher capacities and improved capacity retention over 250 cycles and lower impedance were observed, as the carbon content of LTO-C heterostructures was increased from 0% (LTO nanosheets) to 30%. These results indicate that the self-assembly approach for 2D heterostructured electrode materials is a promising strategy to overcome electronic transport limitations of layered transition-metal oxides and improve their electrochemical performance for next-generation energy storage applications.

25 ENERGY STORAGE↗
DOE OSTI2021

Tutorial on Chemical Pressure Analysis: How Atomic Packing Drives Laves/Zintl Intergrowth in K3Au5Tl

The tight atomic packing generally exhibited by alloys and intermetallics can create the impression of their being composed of hard spheres arranged to maximize their density. As such, the atomic size factor has historically been central to explanations of the structural chemistry of these systems. However, the role atomic size plays structurally has traditionally been inferred from empirical considerations. The recently developed DFT-Chemical Pressure (CP) analysis has opened a path to investigating these effects with theory. In this article, we provide a step-by-step tutorial on the DFT-CP method for non-specialists, along with advances in the approach that broaden its applicability. A new version of the CP software package is introduced, which features an interactive system that guides the user in preparing the necessary electronic structure data and generating the CP scheme, with the results being readily visualized with a web browser (and easily incorporated into websites). For demonstration purposes, we investigate the origins of the crystal structure of K3Au5Tl, which represents an intergrowth of Laves and Zintl phase domains. Here, CP analysis reveals that the intergrowth is supported by complementary CP features of NaTl-type KTl and MgCu2-type KAu2 phases. In this way, K3Au5Tl exemplifies how CP effects can drive the merging for geometrical motifs derived from different families of intermetallics through a mechanism referred to as epitaxial stabilization.

36 MATERIALS SCIENCE↗