Flux synthesis, modulated crystal structures, and physical properties of REMn_0.5SeO (RE = La, Ce)

The selenide oxides REMn_0.5SeO (RE = La, Ce) were synthesized by heating RE₂O₃, 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(αβ1/2)0s, Z = 2, LaMn_0.5SeO: a = 405.7(1), b = 405.7(1), c = 915.2(1) pm, γ = 90 , q = [1/10, -1/10, 1/2]; CeMn_0.5SeO: a = 402.0(1), b = 401.8(1), c = 910.7(1) pm, γ = 90.000(4) , q = [0.0789(2), -0.0783(2), 1/2]}. The structures are related to the ZrCuSiAs-type structure with ordered vacancies at the manganese sites. The resulting modulations of the checkerboard pattern in the [Mn_0.5Se] layers can be approximated by 10a x 10b x 2c and 51a x 51b x 2c supercells in LaMn_0.5SeO and CeMn_0.5SeO, respectively. Both compounds are insulators. The optical bandgap of LaMn_0.5SeO was determined to 2.13 eV from the Kubelka-Munk function. Magnetic measurements indicate antiferromagnetic ordering of the Mn²⁺ moments with Neel points well above room temperature, as known from related manganese compounds. (Copyright copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)