Structural Diversity of Rare-Earth Oxychalcogenides

Abstract

Mixed-anion systems have garnered much attention in the past decade with attractive properties for diverse applications such as energy conversion, electronics, and catalysis. The discovery of new materials through mixed-cation and single-anion systems proved highly successful in the previous century, but solid-state chemists are now embracing an exciting design opportunity by incorporating multiple anions in compounds such as oxychalcogenides. Materials containing rare-earth ions are arguably a cornerstone of modern technology, and herein, we review recent advances in rare-earth oxychalcogenides. We discuss ternary rare-earth oxychalcogenides whose layered structures illustrate the characters and bonding preferences of oxide and chalcogenide anions. We then review quaternary compounds which combine anionic and cationic design strategies toward materials discovery and describe their structural diversity. Finally, we emphasize the progression from layered two-dimensional compounds to three-dimensional networks and the unique synthetic approaches which enable this advancement.

Photocatalytic and Photocurrent Responses to Visible Light of the Lone-Pair-Based Oxysulfide Sr6Cd2Sb6S10O7

“…The driving forces for significant anion-segregation in oxysulfides (giving predominantly homoleptic cation coordination and often layered structures) versus more mixing of anions and heteroleptic coordination environments are not fully explored but may be related to the relative softness/hardness of the specific combination of cations and anions. 72 It is striking that a strong electron−hole separation is indicated by the shape of the photocurrent response in both Sr 6 Cd 2 Sb 6 S 10 O 7 (Figure 6) and LaGaS 2 O. 68 It has been proposed that polar aspects of the structure enhance electron−hole separation in oxysulfides 19 and comparison of these two systems can be instructive.…”

Versatility of Tellurium in Heteroanionic Ln2O2Te (Ln = La, Ce, Pr) and Tellurate Ln2TeO6 (Ln = La, Pr)

“…In this structure, the anions segregate into alternating [Ln 2 O 2 ] 2+ and Te 2– layers. Puckered two-dimensional [Ln 2 O 2 ] 2+ layers contain fluorite-like OLn 4 tetrahedra, a common structural feature among oxychalcogenides, , with edge-sharing connectivity (Figure b), and these are related by an ab mirror plane along [001]. The symmetry of the [Ln 2 O 2 ] 2+ layers in Ln 2 O 2 Te differs from that of Ln 2 O 2 Q (Q = S, Se), where [Ln 2 O 2 ] 2+ layers are simply translated along [001] (with no mirror plane) .…”

“…Puckered two-dimensional [Ln 2 O 2 ] 2+ layers contain fluorite-like OLn 4 tetrahedra, a common structural feature among oxychalcogenides, , with edge-sharing connectivity (Figure b), and these are related by an ab mirror plane along [001]. The symmetry of the [Ln 2 O 2 ] 2+ layers in Ln 2 O 2 Te differs from that of Ln 2 O 2 Q (Q = S, Se), where [Ln 2 O 2 ] 2+ layers are simply translated along [001] (with no mirror plane) . The larger interlayer spacing of ∼4.14 Å in Ln 2 O 2 Te, compared to ∼3.89–4.11 Å in Ln 2 O 2 Q (Q = S, Se), can accommodate larger Te 2– anions.…”

“…Heteroanionic systems have emerged as a distinct class of materials for which exploration of the anion composition presents an exciting opportunity to strategically target new materials and tune physical properties. − Greater structural diversity afforded by the expanded composition space often results in interesting characteristics otherwise inaccessible through conventional cation substitution or homoanionic systems. As a result of modern computationally driven materials screening techniques, heteroanionic systems are highlighted as promising candidates in advanced applications such as transparent semiconductors, solid-state electrolytes, thermoelectrics, and optoelectronics. − Work on ternary and quaternary heteroanionic systems like oxysulfides, oxyselenides, oxynitrides, and oxychlorides are well underway; however, relatively few oxytellurides have been reported. − This lack of attention is perhaps a reflection of the low natural abundance of tellurium and the invalid assumption that structure–property relationships of tellurium compounds can be inferred from those of their lighter chalcogen counterparts …”

La4Ga2Se6O3: A Rare-Earth Oxyselenide Built from One-Dimensional Strips

“…Among mixed-anion compounds, − quaternary rare-earth oxychalcogenides RE–M–Ch– O (where M is a d- or p-block metal or metalloid) form a diverse group that holds promise for many materials applications. , Well-known examples include transparent semiconductors (LaCuSO), ionic conductors (LaAgSO), photocatalysts (Sm 2 Ti 2 S 2 O 5 ), and thermoelectrics (LaBiS 2 O) . The consideration of such oxychalcogenides as potential thermoelectric materials is relatively recent .…”