New Layered Manganese Oxychlorides
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New Layered Manganese Oxychlorides Christopher S. Knee and Mark T. Weller Inorganic Materials Group Dept. of Chemistry University of Southampton SO17 1BJ UK ABSTRACT
The synthesis, structure and preliminary magnetic characteristics of the new layered manganese oxide chlorides, Sr2MnO3Cl and Sr4Mn3O8-yCl2 are reported. Sr2MnO3Cl adopts a K2NiF4 type structure with sheets of MnO5 square based pyramids linked through oxygen and separated by SrCl layers; it is the end member of a new family of Ruddlesden-Popper type manganese oxide halides which includes the 3-layer member Sr4Mn3O8-yCl2. Magnetic susceptibility measurements reveal antiferromagnetic transitions at 95 K and 90 K for Sr2MnO3Cl and Sr4Mn3O8-yCl2 respectively. These materials demonstrate the extension of mixed anion chemistry to manganese and will increase flexibility in designing and controlling oxidation states of new GMR materials.
INTRODUCTION
The search for new layered transition metal oxides, which exhibit unusual properties such as superconductivity or magnetoresistance, has also led to the development of new mixed anion systems. One such group of materials, which has received renewed interest, is the RuddlesdenPopper oxyhalide family. These systems offer enhanced flexibility over pure oxides both from a structural viewpoint and from their ability to control the transition metal oxidation state as exemplified by the superconducting oxyfluoride Sr2CuO2F2+δ [1]. Recent developments in this area include the cobalt oxychlorides, Sr2CoO3Cl and Srn+1ConO3n-1Cl2 with n = 2, 3 [2]. We have successfully expanded this family with the synthesis of the first manganese oxychlorides, Sr2MnO3Cl and Sr4Mn3O8-yCl2 [3] of interest as potential giant magnetoresistance (GMR) phases. This paper presents details of the synthesis, structures and magnetic properties of these materials. D7.33.1 Downloaded from https://www.cambridge.org/core. The Librarian-Seeley Historical Library, on 11 Jan 2020 at 00:12:56, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-718-D7.33
EXPERIMENTAL
Stoichiometric amounts of high purity SrO, SrCl2 and Mn2O3 were ground in a dry box, transferred to silica vessels, sealed under vacuum and reacted at 850 °C. The single layer phase, Sr2MnO3Cl, formed after a single 20 h firing whilst the three layer material, Sr4Mn3O8-yCl2, required two 14 h anneals with an intermediate regrind. Phase purity was assessed using powder X-ray diffraction data collected on a Bruker D8 diffractometer (Cu Kα1 radiation). The only impurity apparent for Sr4Mn3O8-yCl2 was a small level of MnO whilst the Sr2MnO3Cl sample contained a small level of Sr4Mn3O8-yCl2. Further high quality powder X-ray data were collected in the 2θ range 10-100 ° step size 0.017 ° and structural models derived from Sr2FeO3Cl [4] and Sr4Co3O7.5Cl2 [2] refined using Rietveld profile analysis to give the structural parameters summarised in Tables 1 and 2 below.
Table 1. Derived atomic co-ordinates for Sr2MnO3Cl.
Sr(1) Sr
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