Infinitely Adaptive Transition Metal Oxychalcogenides: The Modulated Structures of Ce2O2MnSe2 and (Ce0.78La0.22)2O2MnSe2

Wang, Chun-Hai; Ainsworth, Chris M.; Gui, Dong-Yun; McCabe, Emma E.; Tucker, Matthew G.; Evans, Ivana R.; Evans, John S.O.

Abstract

This article reports the syntheses, structures, and physical properties of the oxychalcogenides (Ce1–xLax)2O2MnSe2 with x = 0–0.7. These materials have a layered structure related to that of the LaOFeAs-derived superconductors but with the transition metal sites 50% occupied. Ce2O2MnSe2 contains alternating layers of composition: [Ce2O2]2+ and [MnSe2]2–. The size mismatch between the layers leads to an incommensurate structure with a modulation vector of q = αa*+ 0b*+0.5c* with α = 0.158(1), which can be described with a (3 + 1)D superspace structural model in superspace group Cmme(α,0,1/2)0s0 [67.12]. There is a strong modulation of Mn site occupancies, leading to a mixture of corner- and edge-sharing MnSe4/2 tetrahedra in the [MnSe2]2– layers. The modulation vector can be controlled by partial substitution of Ce3+ for larger La3+, and a simple commensurate case was obtained for (Ce0.78La0.22)2O2MnSe2 with α = 1/6. The materials respond to the change in relative size of the oxide and chalcogenide blocks by varying the ratio of corner- to edge-sharing tetrahedra. The superspace model lets us unify the structural description of the five different ordering patterns reported to date for different Ln2O2MSe2 (Ln = lanthanide) materials. Mn moments in Ce2O2MnSe2 and (Ce0.78La0.22)2O2MnSe2 order antiferromagnetically below TN = 150 K, and Ce moments order below ∼70 K. The magnetic structures of both materials have been determined using neutron diffraction. Both materials are semiconductors; Ce2O2MnSe2 has σ = 9 × 10–6 Ω–1 cm–1 at room temperature and an activation energy for charge carrier mobility from RT to 170 °C of ∼0.4 eV.

Citation

Wang, C., Ainsworth, C. M., Gui, D., McCabe, E. E., Tucker, M. G., Evans, I. R., & Evans, J. S. (2015). Infinitely Adaptive Transition Metal Oxychalcogenides: The Modulated Structures of Ce2O2MnSe2 and (Ce0.78La0.22)2O2MnSe2. Chemistry of Materials, 27(8), 3121-3134. https://doi.org/10.1021/acs.chemmater.5b00666

• Journal Article Type: Article
• Online Publication Date: Apr 2, 2015
• Publication Date: Apr 28, 2015
• Deposit Date: May 4, 2015
• Publicly Available Date: Apr 10, 2016
• Journal: Chemistry of Materials
• Print ISSN: 0897-4756
• Electronic ISSN: 1520-5002
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 27
• Issue: 8
• Pages: 3121-3134
• DOI: https://doi.org/10.1021/acs.chemmater.5b00666
• Public URL: https://durham-repository.worktribe.com/output/1430030