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All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Materials Data on Eu5As4 by Materials Project

Eu5As4 crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. there are two inequivalent Eu+2.40+ sites. In the first Eu+2.40+ site, Eu+2.40+ is bonded to six As3- atoms to form a mixture of distorted edge, face, and corner-sharing EuAs6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 38–43°. There are a spread of Eu–As bond distances ranging from 3.09–3.23 Å. In the second Eu+2.40+ site, Eu+2.40+ is bonded to six As3- atoms to form a mixture of face and corner-sharing EuAs6 octahedra. The corner-sharing octahedral tilt angles are 53°. There are a spread of Eu–As bond distances ranging from 3.08–3.18 Å. There are two inequivalent As3- sites. In the first As3- site, As3- is bonded to seven Eu+2.40+ atoms to form a mixture of distorted edge and corner-sharing AsEu7 pentagonal bipyramids. In the second As3- site, As3- is bonded in a 9-coordinate geometry to eight Eu+2.40+ and one As3- atom. The As–As bond length is 2.83 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Completing the Ba–As Compositional Space: Synthesis and Characterization of Three New Binary Zintl Arsenides, Ba3As4, Ba5As4, and Ba16As11

Three novel binary barium arsenides, Ba3As4, Ba5As4, and Ba16As11, were synthesized and their crystal and electronic structures were investigated. Structural data collected via the single-crystal X-ray diffraction method indicate that the anionic substructures of all three novel compounds are composed of structural motifs based on the homoatomic As–As contacts, with [As2]4− dimers found in Ba5As4 and Ba16As11, and an [As4]6− tetramer found in Ba3As4. Ba3As4 and Ba5As4 crystallize in the orthorhombic crystal system—with the non-centrosymmetric space group Fdd2 (a = 15.3680(20) Å, b = 18.7550(30) Å, c = 6.2816(10) Å) for the former, and the centrosymmetric space group Cmce (a = 16.8820(30) Å, b = 8.5391(16) Å, and c = 8.6127(16) Å) for the latter—adopting Eu3As4 and Eu5As4 structure types, respectively. The heavily disordered Ba16As11 structure was solved in the tetragonal crystal system with the space group P4¯21m (a = 12.8944(12) Å and c = 11.8141(17) Å). The Zintl concept can be applied to each of these materials as follows: Ba3As4 = (Ba2+)3[As4]6−, Ba5As4 = (Ba2+)5(As3−)2[As2]4−, and 2 × Ba16As11 = (Ba2+)32(As3−) ≈ 20[As2]4− ≈ 1, pointing to the charge-balanced nature of these compounds. Electronic structure calculations indicate narrow bandgap semiconducting behavior, with calculated bandgaps of 0.47 eV for Ba3As4, 0.34 eV for Ba5As4, and 0.33 eV for Ba16As11.

Crystallography↗