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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on KAu2 by Materials Project

KAu2 is Hexagonal Laves structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. K is bonded in a 12-coordinate geometry to twelve Au atoms. There are a spread of K–Au bond distances ranging from 3.38–3.52 Å. There are two inequivalent Au sites. In the first Au site, Au is bonded to six equivalent K and six equivalent Au atoms to form a mixture of distorted corner, edge, and face-sharing AuK6Au6 cuboctahedra. All Au–Au bond lengths are 3.00 Å. In the second Au site, Au is bonded to six equivalent K and six Au atoms to form a mixture of corner, edge, and face-sharing AuK6Au6 cuboctahedra. There are two shorter (2.88 Å) and two longer (2.89 Å) Au–Au bond lengths.

36 MATERIALS SCIENCE↗
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↗