Flux Synthesis, Crystal Structures, and Magnetic Ordering of the Rare-Earth Chromium(II) Oxyselenides RE₂CrSe₂O₂ (RE = La–Nd)

Abstract

The rare-earth chromium(II) oxyselenides RECrSeO (RE = La-Nd) were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined by single-crystal and powder X-ray diffraction (PbHgClO-type, C2/m, Z = 2). The magnetic structure of LaCrSeO was solved and refined from neutron powder diffraction data. Main building blocks are chains of edge-sharing CrSeO octahedra linked together by two edge-sharing ORECr tetrahedra forming infinite ribbons. The Jahn-Teller instability of divalent Cr (d) leads to structural phase transitions at 200 and 130 K in LaCrSeO and CeCrSeO, respectively. RECrSeO are Curie-Weiss paramagnetic above T ≈ 14-17 K. Neutron powder diffraction reveals anti-ferromagnetic ordering of the Cr moments in LaCrSeO below T = 12.7(3) K with an average ordered moment of 3.40(4) μ/Cr at 4 K, which was confirmed by muon spin rotation experiments.

Structural Diversity of Rare-Earth Oxychalcogenides

“…Ln 2 O 2 CrSe 2 adopts structures closely related to CeCrOS 2 but with CrO 2 Se 4 chains (instead of CrS 6 octahedra) separated by ribbons of two OLn 3 Cr tetrahedra . Hysteretic structural phase transitions are associated with second-order Jahn–Teller distortions of the Cr 2+ (d 4 ) ions.…”

“Soft” Alkali Bromide and Iodide Fluxes for Crystal Growth

“…The ABI fluxes have also been employed to synthesize a variety of oxychalcogenide compounds. These are predominately oxyselenides (Tougait and Ibers, 2000b , c , 2001 ; Nitsche et al, 2014 ; Liu et al, 2015 ; Peschke et al, 2015 , 2017a , b ; Peschke and Johrendt, 2016 , 2017 ), but also include oxysulfides (Zeng et al, 1999 , 2002 ; Huang et al, 2000 ; Chi et al, 2016 ), and oxytellurides (Liu et al, 2007 ). In many cases, the ABI flux is utilized as a recrystallizing agent.…”

Synthesis, Crystal Structure, and Physical Properties of Layered LnCrSe2O (Ln = Ce–Nd)

“…Heteroanionic compounds have been of continuing interest for decades, especially since the discovery of the high-temperature superconductors Ln OFeAs ( Ln = La, Ce, Pr, Nd, Sm). − Among these heteroanionic compounds, oxychalcogenides have been a topic of research for the intriguing crystal structures and intertwined chemical/​physical properties they possess. − For instance, the layered LaOCuS and BiOCuSe semiconductors, which are constructed by alternatively stacking of the PbO- and anti-PbO-type of layers, have been identified as good transparent conductor and thermoelectric material, respectively. − Recently, the reports of outstanding photoresponse (to visible and NIR light) properties and ultrahigh electron motilities of layered bismuth oxychalcogenides (Bi 2 O 2 Q , Q = S, Se) give rise to a new upsurge of research on oxychalcogenides. The intriguing crystal structures of oxychalcogenides are attributed to the distinct packing habits of O 2– and Q 2– ( Q = S, Se, Te).…”

“…Therefore, the chromium-based oxychalcogenides shall have diversified physical properties. Despite the numerous research activities on the chromium oxide and chromium chalcogenides and their chemical/​physical properties, reports about new chromium-based oxychalcogenides are rare. ,− To date, the most famous chromium based oxychalcogenides are the quasi-one-dimensional LaCr Q 2 O ( Q = S, Se) for their ferromagnetic phase transition at low temperature ( Q = S, T C = 35 K; Q = Se, T C = 51 K). , The isostructural Ln CrS 2 O ( Ln = Ce, Pr, Nd) and CeCrSe 2 O, possessing a layered structure, are also reported with antiferromagnetic phase transition at 83 K (PrCrS 2 O) and 72 K (NdCrS 2 O), respectively. ,− Most recently, a series of new rare-earth chromium­(II) oxyselenides Ln 2 CrSe 2 O 2 ( Ln = La–Nd) have been synthesized via a flux method, which are antiferromagnetic compounds with T N ≈ 14–17 K . Nevertheless, more chromium-based oxychalcogenides, especially oxyselenides, should be explored to uncover new physical phenomena.…”

“…39,40 The isostructural LnCrS 2 O (Ln = Ce, Pr, Nd) and CeCrSe 2 O, possessing a layered structure, are also reported with antiferromagnetic phase transition at 83 K (PrCrS 2 O) and 72 K (NdCrS 2 O), respectively.39,41−43 Most recently, a series of new rare-earth chromium(II) oxyselenides Ln 2 CrSe 2 O 2 (Ln = La−Nd) have been synthesized via a flux method, which are antiferromagnetic compounds with T N ≈ 14−17 K 8. Nevertheless, more chromium-based oxychalcogenides, especially oxyselenides, should be explored to uncover new physical phenomena.In this work, we present the structure and physical properties of two new layered chromium oxyselenides, namely the LnCrSe 2 O (Ln = Pr, Nd), which were synthesized via the molten salt methods.For comparison, CeCrSe 2 O was also synthesized.…”