Browsing by Author "Ainsworth, CM"

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    3D transition metal ordering and Rietveld stacking fault quantification in the new oxychalcogenides La2O2Cu2–4xCd2xSe2
    (American Chemical Society, 2016-04-04) Ainsworth, CM; Lewis, JW; Wang, CH; Coelho, AA; Johnston, HE; Brand, HEA; Evans, JSO
    A number of LnOCuCh (Ln = La-Nd, Bi; Ch = S, Se, Te) compounds have been reported in the literature built from alternating layers of fluorite-like [Ln2O2]2+ sheets and antifluorite-like [M2Se2]2- sheets, where M is in the +1 oxidation state leading to full occupancy of available MSe4/2 tetrahedral sites. There is also a family of related LnOM0.5Se (Ln = La & Ce, M = Fe, Zn, Mn & Cd) compounds built from alternating layers of [Ln2O2]2+ sheets and [MSe2]2- sheets, where M is in the +2 oxidation state with half occupancy of available tetrahedral sites and complex ordering schemes in two dimensions. This paper reports a new family of compounds containing both +1 and +2 metal ions in the La2O2Cu2-4xCd2xSe2 family. We show how Cu1+ and Cd2+ ions segregate into distinct fully occupied and half occupied checkerboard-like layers respectively, leading to complex long-range superstructures in the third (stacking) dimension. To understand the structure and microstructure of these new materials we have developed and implemented a new methodology for studying low and high probability stacking faults using a Rietveld-compatible supercell approach capable of analyzing systems with thousands of layers. We believe this method will be widely applicable. © 2016 American Chemical Society.
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    Crystal structure and magnetic modulation in β−Ce2O2FeSe2
    (American Physical Society, 2017-08-11) Wang, CH; Ainsworth, CM; Champion, SD; Stewart, GA; Worsdale, MC; Lancaster, T; Blundell, SJ; Brand, HEA; Evans, JSO
    We report a combination of x-ray and neutron diffraction studies, Mössbauer spectroscopy, and muon spin relaxation (μ+SR) measurements to probe the structure and magnetic properties of the semiconducting β-Ce2O2FeSe2 oxychalcogenide. We report a structural description in space group Pna21 which is consistent with diffraction data and second harmonic generation measurements and reveal an order-disorder transition on one Fe site at TOD≈330K. Susceptibility measurements, Mössbauer, and μ+SR reveal antiferromagnetic ordering below TN=86K and more complex short range order above this temperature. 12 K neutron diffraction data reveal a modulated magnetic structure with q=0.444bN∗. © 2017 American Physical Society.
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    Infinitely adaptive transition-metal ordering in Ln2O2MSe2-type oxychalcogenides
    (American Chemical Society, 2015-04-30) Ainsworth, CM; Wang, CH; Johnston, HE; McCabe, EE; Tucker, MG; Brand, HEA; Evans, JSO
    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. © 2015 American Chemical Society