Abstract
Molten salts are promising reaction media candidates for the discovery of novel materials; however, they offer little control over oxidation state compared to aqueous solutions. Here, we demonstrated that when two hydroxides are mixed, their melts become fluxes with tunable solubility, which are surprisingly powerful solvents for ternary chalcogenides and offer effective paths for crystal growth to new compounds. We report that precise control of the oxidation state of Ni is achievable in mixed molten LiOH/KOH to grow single crystals of all known ternary K-Ni-S compounds. It is also possible to access several new phases, including a new polytope of β-K2Ni3S4, as well as low-valence KNi4S2 and K4Ni9S11. KNi4S2 is a two-dimensional low-valence nickel-rich sulfide, and β-K2Ni3S4 has a hexagonal lattice. Moreover, using KNi4S2 as a template, we obtained a new layered binary Ni2S by topotactic deintercalation of K. The new binary Ni2S has a van der Waals gap and can function as a new host layer for intercalation chemistry, as demonstrated by the intercalation of LiOH between its layers. The oxidation states of low-valence KNi4S2 and Ni2S were studied using X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. Density functional theory calculations showed large antibonding interactions at the Fermi level for both KNi4S2 and Ni2S, corresponding to the flat-bands with large Ni-dx2-y2 character.
| Original language | English |
|---|---|
| Pages (from-to) | 13646-13654 |
| Number of pages | 9 |
| Journal | Journal of the American Chemical Society |
| Volume | 143 |
| Issue number | 34 |
| DOIs | |
| State | Published - Sep 1 2021 |
Funding
This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences, and the Engineering Division. EDS/SEM and TEM/EELS analyses were carried out at the Center for Nanoscale Materials (CNM), which is the Office of Science user facilities supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Work at the 17-BM and 20-BM beamlines at the Advanced Photon Source (APS) at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract No. DE-AC02-06CH11357. H. Park was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences, and Engineering Division. H.P. acknowledges the computing resources provided by Bebop, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory.