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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on FeSi2 by Materials Project

FeSi2 crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. there are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a 8-coordinate geometry to eight Si atoms. There are a spread of Fe–Si bond distances ranging from 2.33–2.43 Å. In the second Fe site, Fe is bonded in a 8-coordinate geometry to eight Si atoms. There are a spread of Fe–Si bond distances ranging from 2.33–2.38 Å. There are two inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to four Fe and five Si atoms. There are a spread of Si–Si bond distances ranging from 2.47–2.58 Å. In the second Si site, Si is bonded in a 9-coordinate geometry to four Fe and five Si atoms. There are one shorter (2.53 Å) and one longer (2.56 Å) Si–Si bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeSi2 by Materials Project

FeSi2 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Fe is bonded in a body-centered cubic geometry to eight equivalent Si atoms. All Fe–Si bond lengths are 2.37 Å. Si is bonded in a 9-coordinate geometry to four equivalent Fe and one Si atom. The Si–Si bond length is 2.34 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Quantitative phase imaging around water vapor microbubbles under pulsed laser illumination

We measured water temperature around a self-oscillating water vapor-rich bubble using diffraction phase microscopy equipped with a pulsed laser. The water vapor-rich bubble, which causes a strong water flow around it, was generated by locally heating degassed water through the photothermal conversion properties of an FeSi2 thin film. The generation of the flow is related to the self-oscillation of the bubble at sub-MHz frequencies and the temperature distribution around it. Here, the refractive index of the surrounding water was measured using a pulsed laser with a 3.5-ns pulse duration, which guarantees a time resolution of less than 1/200 of the oscillation cycle of the bubble. The temperature distribution around the bubble was calculated from the measured refractive index.

Narihira, Kyoshiro [Kyoto University, Japan]↗
DOE OSTI2023

Understanding the Formation of Complex Phases: The Case of FeSi 2

One of the fundamental goals of materials science is to understand and predict the formation of complex phases. In this study, FeSi 2 is considered as an illustration of complex phase formation. Although Fe and Si both crystallize with a simple structure, namely, body-centered cubic (bcc A2) and diamond (A4) structures, respectively, it is rather intriguing to note the existence of two complex structures in the Si-rich part of the phase diagram around FeSi 2 : α-FeSi 2 at high temperatures (HT) with a slight iron-deficient structure and β-FeSi2 (also referred to as Fe 3 Si 7 ) at low temperatures (LT). We re-analyze the geometry of these two phases and rely on approximant phases that make the relationship between these two phases simple. To complete the analysis, we also introduce a surrogate of the C16 phase that is observed in FeGe 2 . We clearly identify the relationship that exists between these three approximant phases, corroborated by a ground-state analysis of the Ising model for describing ordering that takes place between the transition metal element and the “vacancies”. This work is further supported by ab initio electronic structure calculations based on density functional theory in order to investigate properties and transformation paths. Finally, extension to other alloys, including an entire class of alloys, is discussed.

36 MATERIALS SCIENCE↗