Infinitely Adaptive Transition-Metal Ordering in Ln₂O₂MSe₂-Type Oxychalcogenides

Abstract

A number of Ln2O2MSe2 (Ln = La and Ce; M = Fe, Zn, Mn, and Cd) compounds, built from alternating layers of fluorite-like [Ln2O2](2+) sheets and antifluorite-like [MSe2](2-) sheets, have recently been reported in the literatures. The available MSe4/2 tetrahedral sites are half-occupied, and different compositions display different ordering patterns: [MSe2](2-) layers contain MSe4/2 tetrahedra that are exclusively edge-sharing (stripe-like), exclusively corner-sharing (checkerboard-like), or mixtures of both. This paper reports 60 new compositions in this family. We reveal that the transition-metal arrangement can be systematically controlled by either Ln or M doping, leading to an "infinitely adaptive" structural family. We show how this is achieved in La2O2Fe1-xZnxSe2, La2O2Zn1-xMnxSe2, La2O2Mn1-xCdxSe2, Ce2O2Fe1-xZnxSe2, Ce2O2Zn1-xMnxSe2, Ce2O2Mn1-xCdxSe2, La2-yCeyO2FeSe2, La2-yCeyO2ZnSe2, La2-yCeyO2MnSe2, and La2-yCeyO2CdSe2 solid solutions.

3D Transition Metal Ordering and Rietveld Stacking Fault Quantification in the New Oxychalcogenides La2O2Cu2–4xCd2xSe2

“…14, 15 Here we show that this complexity can be extended to 3 dimensions in a new family of mixed metal oxychalcogenides. We unravel their crystal chemistry from powder diffraction studies, despite stacking faults leading to nonroutine peak shapes.…”

“…[5][6][7] Perhaps the most famous compounds with this structure type are derived from LaOFeAs, and [16][17][18][19][20] superconduct at temperatures up to 55 K. 1,2 We and others have recently reported the structures of a range of related compounds containing 2+ metals, where charge balance leads to half the available metal sites in the tetrahedral layers being occupied and composition Ln 2 O 2 MSe 2 . [13][14][15][22][23][24][25][26][27] In the case of M = Cd this leads to the simple checkerboard (or Z 4 -) ordering pattern of Figure 1 in which tetrahedra are exclusively corner-shared. 23 In other systems (M = Fe, Mn, Zn, Cd and combinations thereof) the high rigidity of the [Ln 2 O 2 ] 2+ layer can be used to tune the M 2+ architecture from exclusively corner-sharing (e.g.…”

Crystal structure and magnetic modulation in β−Ce2O2FeSe2

“…One important family of compounds is those with general composition Ln 2 O 2 MSe 2 (Ln = La, Ce; M = Mn, Fe, Zn, Cd) [3][4][5][6][7][8][9][10][11] and closely related composition such as La 2 O 2 Cu 2−4x Cd 2x Se 2 [12]. These materials are semiconductors with band gaps varying from ∼0.3 to ∼3.3 eV [1,[3][4][5]8,10,11,[13][14][15][16]. For example, layered La 2 O 2 CdSe 2 was reported as a wide-gap (3.3 eV) semiconductor and investigated as an optoelectronic device component [14,15].…”

“…Three basic structure types have been observed for Ln 2 O 2 MSe 2 compositions to date. Most adopt a layered structure (α phase) which can be modulated in either a commensurate or incommensurate manner within individual layers to accommodate different transition metal arrangements [8,10,11]. There are also two nonlayered structures reported (orthorhombic β phase and monoclinic Pb 2 HgCl 2 O 2 -type γ phase) [3,13].…”

Flux Synthesis, Crystal Structures, and Magnetism of the Series La2n+2MnSen+2O2n+2 (n = 0–2)

“…Numerous new compounds with the general formula RE 2 TSe 2 O 2 (RE = La, Ce; T = Cd, Fe, Mn, Zn) [1][2][3][4][5][6][7][8][9] have been discovered and their structures and magnetism have been studied. Among the particular families, different polymorphs may exist which makes the diversity even bigger.…”