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Infinitely adaptive transition metal oxychalcogenides : the modulated structures of Ce2O2MnSe2 and (Ce0.78La0.22)2O2MnSe2.

Wang, Chun-Hai and Ainsworth, Chris M. and Gui, Dong-Yun and McCabe, Emma E. and Tucker, Matthew G. and Evans, Ivana R. and Evans, John S. O. (2015) 'Infinitely adaptive transition metal oxychalcogenides : the modulated structures of Ce2O2MnSe2 and (Ce0.78La0.22)2O2MnSe2.', Chemistry of materials., 27 (8). pp. 3121-3134.

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.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1021/acs.chemmater.5b00666
Publisher statement:This document is the Accepted Manuscript version of a Published Work that appeared in final form in Chemistry of Materials, copyright © 2015 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.chemmater.5b00666.
Date accepted:No date available
Date deposited:06 May 2015
Date of first online publication:02 April 2015
Date first made open access:10 April 2016

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