Layered CeSO and LiCeSO Oxide Chalcogenides Obtained via Topotactic Oxidative and Reductive Transformations

Abstract

The chemical accessibility of the CeIV oxidation state enables redox chemistry to be performed on the naturally coinage-metal-deficient phases CeM1– x SO (M = Cu, Ag). A metastable black compound with the PbFCl structure type (space group P4/nmm: a = 3.8396(1) Å, c = 6.607(4) Å, V = 97.40(6) Å3) and a composition approaching CeSO is obtained by deintercalation of Ag from CeAg0.8SO. High-resolution transmission electron microscopy reveals the presence of large defect-free regions in CeSO, but stacking faults are also evident which can be incorporated into a quantitative model to account for the severe peak anisotropy evident in all the high-resolution X-ray and neutron diffractograms of bulk CeSO samples; these suggest that a few percent of residual Ag remains. A straw-colored compound with the filled PbFCl (i.e., ZrSiCuAs- or HfCuSi2-type) structure (space group P4/nmm: a = 3.98171(1) Å, c = 8.70913(5) Å, V = 138.075(1) Å3) and a composition close to LiCeSO, but with small amounts of residual Ag, is obtained by direct reductive lithiation of CeAg0.8SO or by insertion of Li into CeSO using chemical or electrochemical means. Computation of the band structure of pure, stoichiometric CeSO predicts it to be a Ce4+ compound with the 4f-states lying approximately 1 eV above the sulfide-dominated valence band maximum. Accordingly, the effective magnetic moment per Ce ion measured in the CeSO samples is much reduced from the value found for the Ce3+-containing LiCeSO, and the residual paramagnetism corresponds to the Ce3+ ions remaining due to the presence of residual Ag, which presumably reflects the difficulty of stabilizing Ce4+ in the presence of sulfide (S2– ). Comparison of the behavior of CeCu0.8SO with that of CeAg0.8SO reveals much slower reaction kinetics associated with the Cu1– x S layers, and this enables intermediate CeCu1– x ­Li x SO phases to be isolated.

Computational Discovery of Stable Heteroanionic Oxychalcogenides ABXO (A, B = Metals; X = S, Se, and Te) and Their Potential Applications

“…We note that despite being predicted to be thermodynamically stable, the experimental synthesis of many of these compounds may be challenging. For example, the only known example of a Li-containing ABXO compound, LiCeSO, was only very recently synthesized by inserting Li into CeSO using chemical or electrochemical methods . BiAgSO and BiAgSeO were also only recently reported to be synthesized via ion exchange of Cu with Ag in pH- and T-controlled aqueous environments. , …”

“…However, many oxychalcogenide compounds are actually prepared by classical solid-state reactions . A number of other approaches also have been used to synthesize oxychalcogenide compounds, such as soft-chemistry, solvothermal synthesis, ,, thin-film growth, high-pressure synthesis, ion exchange, and topotactic reductive transformation . Different approaches have to be chosen according to the properties of the precursors.…”

“…For example, the only known example of a Licontaining ABXO compound, LiCeSO, was only very recently synthesized by inserting Li into CeSO using chemical or electrochemical methods. 87 BiAgSO and BiAgSeO were also only recently reported to be synthesized via ion exchange of Cu with Ag in pH-and T-controlled aqueous environments. 84,85 Electronic Structure.…”

“…14 A number of other approaches also have been used to synthesize oxychalcogenide compounds, such as soft-chemistry, 133 solvothermal synthesis, 85,134,135 thin-film growth, 112 highpressure synthesis, 136 ion exchange, 84 and topotactic reductive transformation. 87 Different approaches have to be chosen according to the properties of the precursors. DFT calculations also can assist experimental synthesis to find the best synthesis conditions.…”

Anion Redox as a Means to Derive Layered Manganese Oxychalcogenides with Exotic Intergrowth Structures

“…Synthetic intermediates may circumvent large activation barriers, which are often encountered during topochemical anion redox. For example, the topochemical conversion of LaOCuS to LaOS required a reaction temperature of 200 °C14 while conversion of CeOAg0.8S to CeSO, involving Ce 3+/4+ redox instead of S 2-/redox, proceeded at ambient temperature 16 . Kinetic barriers during anion redox are known to be an adverse factor causing voltage hysteresis in secondary battery systems.…”