Flux Synthesis, Modulated Crystal Structures, and Physical Properties of REMn_0.5SeO (RE = La, Ce)

Abstract

The selenide oxides REMn 0.5 SeO (RE = La, Ce) were synthesized by heating RE 2 O 3 , RE, Mn, and Se in a NaI/KI flux at 800°C, and their modulated crystal structures determined by X-ray single crystal and powder diffraction {P 1 1 2/n(αβ½)0s, Z = 2, LaMn 0.5 SeO: a = 405.7(1), b = 405.7(1), c = 915.2(1) pm, γ = 90°, q = [1/10, -1/10, ½]; CeMn 0.5 SeO: a = 402.0(1), b = 401.8(1), c = 910.7(1) pm, γ = 90.000(4)°, q = [0.0789(2), -0.0783 (2), ½]}. The structures are related to the ZrCuSiAs-type structure with ordered vacancies at the manga-

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

“…Powder samples and single crystals of mC-La 2 MnSe 2 O 2 were prepared in a NaI/KI-flux starting from oC-La 2 MnSe 2 O 2 , which was prepared as described in Reference [1]. oC-La 2 MnSe 2 O 2 (0.10 g) was sandwiched with 0.30 g of an eutectic mixture of NaI/KI (mass ratio 0.6:0.4, dried in dynamic vacuum at 673 K) in an alumina crucible.…”

“…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.…”

“…Beside the iron compounds, there are two polymorphs known in the analogous manganese family. oC-La 2 MnSe 2 O 2 [1] has a defect ZrCuSiAs-type structure with slabs of edge-sharing OLa 4 -tetrahedra stacked alternating with slabs of MnSe 4 -tetrahedra. The structure of oA-La 2 MnSe 2 O 2 [8] consists of MnSe 4 -tetrahedra and edge-sharing MnSe 4 O 2 -octahedra which are connected by infinite ribbons of edge-sharing OLa 4 -and OLa 3 Mn-tetrahedra four units wide.…”

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].…”