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DOE OSTI2020

Materials Data on FeAsS by Materials Project

FeAsS is Hausmannite-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Fe3+ is bonded to three equivalent As1- and three equivalent S2- atoms to form FeAs3S3 octahedra that share corners with eight equivalent FeAs3S3 octahedra, corners with three equivalent AsFe3S tetrahedra, corners with three equivalent SFe3As tetrahedra, and edges with two equivalent FeAs3S3 octahedra. The corner-sharing octahedra tilt angles range from 52–62°. There are one shorter (2.38 Å) and two longer (2.41 Å) Fe–As bond lengths. There are a spread of Fe–S bond distances ranging from 2.19–2.21 Å. As1- is bonded to three equivalent Fe3+ and one S2- atom to form AsFe3S tetrahedra that share corners with three equivalent FeAs3S3 octahedra, corners with four equivalent AsFe3S tetrahedra, corners with nine equivalent SFe3As tetrahedra, and an edgeedge with one AsFe3S tetrahedra. The corner-sharing octahedra tilt angles range from 69–74°. The As–S bond length is 2.41 Å. S2- is bonded to three equivalent Fe3+ and one As1- atom to form distorted SFe3As tetrahedra that share corners with three equivalent FeAs3S3 octahedra, corners with four equivalent SFe3As tetrahedra, corners with nine equivalent AsFe3S tetrahedra, and an edgeedge with one SFe3As tetrahedra. The corner-sharing octahedra tilt angles range from 76–77°.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on FeAsSe by Materials Project

FeAs(Se) crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Fe3+ is bonded to three equivalent As1- and three equivalent Se2- atoms to form FeAs3Se3 octahedra that share corners with eight equivalent FeAs3Se3 octahedra, corners with three equivalent AsFe3Se tetrahedra, corners with three equivalent SeFe3As tetrahedra, and edges with two equivalent FeAs3Se3 octahedra. The corner-sharing octahedra tilt angles range from 52–59°. There are a spread of Fe–As bond distances ranging from 2.40–2.43 Å. There are two shorter (2.32 Å) and one longer (2.34 Å) Fe–Se bond lengths. As1- is bonded to three equivalent Fe3+ and one Se2- atom to form distorted AsFe3Se tetrahedra that share corners with three equivalent FeAs3Se3 octahedra, corners with four equivalent AsFe3Se tetrahedra, corners with nine equivalent SeFe3As tetrahedra, and an edgeedge with one AsFe3Se tetrahedra. The corner-sharing octahedra tilt angles range from 68–74°. The As–Se bond length is 2.55 Å. Se2- is bonded to three equivalent Fe3+ and one As1- atom to form distorted SeFe3As tetrahedra that share corners with three equivalent FeAs3Se3 octahedra, corners with four equivalent SeFe3As tetrahedra, corners with nine equivalent AsFe3Se tetrahedra, and an edgeedge with one SeFe3As tetrahedra. The corner-sharing octahedra tilt angles range from 76–79°.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Computational search for itinerant n -type and p -type magnetic semiconductors: Arsenopyrites as bipolar magnetic semiconductors

We report a computational search for three-dimensional bulk ferromagnetic semiconductors based on itinerant Stoner physics. Stoner-based ferromagnetic semiconductors require an unusual combination of high band edge density of states and moderate transport effective mass. Nonetheless, several potential materials are found. Here, we identify arsenopyrites, exemplified by FeAsS, as materials that, with suitable doping, exhibit ferromagnetic semiconducting behavior for both n- and p-type dopants. The existence of a material that becomes ferromagnetic for both p and n types may enable device concepts, for example, ferromagnetic p–n junction devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Improved precision in As speciation analysis with HERFD-XANES at the As K -edge: the case of As speciation in mine waste

High-energy-resolution fluorescence-detected (HERFD) X-ray absorption near-edge spectroscopy (XANES) is a spectroscopic method that allows for increased spectral feature resolution, and greater selectivity to decrease complex matrix effects compared with conventional XANES. XANES is an ideal tool for speciation of elements in solid-phase environmental samples. Accurate speciation of As in mine waste materials is important for understanding the mobility and toxicity of As in near-surface environments. In this study, linear combination fitting (LCF) was performed on synthetic spectra generated from mixtures of eight measured reference compounds for both HERFD-XANES and transmission-detected XANES to evaluate the improvement in quantitative speciation with HERFD-XANES spectra. The reference compounds arsenolite (As 2 O 3 ), orpiment (As 2 S 3 ), getchellite (AsSbS 3 ), arsenopyrite (FeAsS), kaňkite (FeAsO 4 ·3.5H 2 O), scorodite (FeAsO 4 ·2H 2 O), sodium arsenate (Na 3 AsO 4 ), and realgar (As 4 S 4 ) were selected for their importance in mine waste systems. Statistical methods of principal component analysis and target transformation were employed to determine whether HERFD improves identification of the components in a dataset of mixtures of reference compounds. LCF was performed on HERFD- and total fluorescence yield (TFY)-XANES spectra collected from mine waste samples. Arsenopyrite, arsenolite, orpiment, and sodium arsenate were more accurately identified in the synthetic HERFD-XANES spectra compared with the transmission-XANES spectra. In mine waste samples containing arsenopyrite and either scorodite or kaňkite, LCF with HERFD-XANES measurements resulted in fits with smaller R -factors than concurrently collected TFY measurements. The improved accuracy of HERFD-XANES analysis may provide enhanced delineation of As phases controlling biogeochemical reactions in mine wastes, contaminated soils, and remediation systems.

58 GEOSCIENCES↗