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The Subchalcogenides Ir2In8Q (Q = S, Se, Te): Dirac Semimetal Candidates with Re-entrant Structural Modulation
journal contribution
posted on 2020-03-24, 14:05 authored by Jason
F. Khoury, Alexander J. E. Rettie, Iñigo Robredo, Matthew J. Krogstad, Christos D. Malliakas, Aitor Bergara, Maia G. Vergniory, Raymond Osborn, Stephan Rosenkranz, Duck Young Chung, Mercouri G. KanatzidisSubchalcogenides
are uncommon compounds where the metal atoms are
in unusually low formal oxidation states. They bridge the gap between
intermetallics and semiconductors and can have unexpected structures
and properties because of the exotic nature of their chemical bonding
as they contain both metal–metal and metal–main group
(e.g., halide, chalcogenide) interactions. Finding new members of
this class of materials presents synthetic challenges as attempts
to make them often result in phase separation into binary compounds.
We overcome this difficulty by utilizing indium as a metal flux to
synthesize large (millimeter scale) single crystals of novel subchalcogenide
materials. Herein, we report two new compounds Ir2In8Q (Q = Se, Te) and compare their structural and electrical
properties to the previously reported Ir2In8S analogue. Ir2In8Se and Ir2In8Te crystallize in the P42/mnm space group and are isostructural to Ir2In8S, but also have commensurately modulated (with q vectors q = 1/6a* + 1/6b* and q = 1/10a* + 1/10b* for Ir2In8Se and Ir2In8Te, respectively) low-temperature phase transitions,
where the chalcogenide anions in the channels experience a distortion
in the form of In–Q bond alternation along the ab plane. Both compounds display re-entrant structural behavior, where
the supercells appear on cooling but revert to the original subcell
below 100 K, suggesting competing structural and electronic interactions
dictate the overall structure. Notably, these materials are topological
semimetal candidates with symmetry-protected Dirac crossings near
the Fermi level and exhibit high electron mobilities (∼1500
cm2 V–1 s–1 at 1.8
K) and moderate carrier concentrations (∼1020 cm–3) from charge transport measurements. This work highlights
metal flux as a synthetic route to high quality single crystals of
novel intermetallic subchalcogenides with Dirac semimetal behavior.
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Keywords
8 TeDirac semimetal behavior8 Senovel intermetallic subchalcogenidesIr 2metal fluxsymmetry-protected Dirac crossingscompounds display re-entrantcompounds Ir 2novel subchalcogenide materialsRe-entrant Structural Modulation SubchalcogenidesSubchalcogenides Ir 2topological semimetal candidates8 S analogueq vectors qcharge transport measurements8 Q
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