Soft chemical control of the crystal structure and properties of Sr₂MnO₂Cu_1.5-δS₂

J. N. Blandy¹, A. M. Abakumov², K. E Christensen¹, J. Hadermann², P. Adamson¹, D. G. Free¹, H. Cohen¹, A. L. Thompson¹ and S. J. Clarke¹

¹Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR
²Electron Microscopy for Materials Science (EMAT), University of Antwerp, Grenenborgerlaan 171, B-2020 Antwerp, Belgium
jack.blandy@chem.ox.ac.uk

Sr₂MnO₂Cu_1.5-δS₂[1] is a constituent compound of the wider class A₂MO₂X₂Ch₂ (A = Sr, Ba; M = 1^st row transition metal, X = Cu, Ag; Ch = S, Se). Previous work on this compound has included investigation of its potential as a Li⁺ ion host in batteries [2] and examination of the solid solution Sr₂MnO₂Cu_1.5S_2-xSe_x.[3] This work explores topotactic oxidation of the manganese ions to synthesise metastable compositions with larger copper deficiencies.[4]

Sr₂MnO₂Cu_1.5S₂ was prepared via solid state synthesis, and then copper was deintercalated using varying concentrations of I₂/MeCN solution. The high mobility of copper in this compound meant that a range of copper occupancies could be obtained between 1.5 and 1.33 with a phase gap in the region 1.39 – 1.35.

Reduction in copper content led to changes in the copper vacancy ordering pattern from that described by Adamson et al.[3], which only appears at temperatures below an ordering temperature of c. 250 K, to an incommensurately modulated ordering pattern, which is present in room temperature samples. This incommensurate ordering pattern was solved using a (3 + 1)D model approach, with modulation vector q = 0.2418 a₀^* and space group Xmmm(α00)00s. It was found that, as well as occupational modulation of the Cu atoms, there was also significant positional modulation of the oxide layers, which moved closer to the [Cu_2-δS₂] layers to ensure that the S atoms did not become underbonded in low Cu regions (fig. 1).

The presentation will also describe the effect of tuning composition and structure on physical properties.

Fig. 1 A representation of the modulated structure obtained from analysis of the single crystal diffraction data. The occupational modulation of the Cu sites is depicted using the size of the green circles

1.    W. J. Zhu and P. H. Hor, J. Solid State Chem., 1997, 130, 319-321.

2.    S. Indris, J. Cabana, O. J. Rutt, S. J. Clarke and C. P. Grey, J.  Am. Chem. Soc., 2006, 128, 13354-13355.

3.    P. Adamson, J. Hadermann, C. F. Smura, O. J. Rutt, G. Hyett, D. G. Free and S. J. Clarke, Chem. Mater., 2012, 24, 2802-2816.

4.    J. N. Blandy, A. M. Abakumov, K. E. Christensen, J. Hadermann, P. Adamson, S. J. Cassidy, S. Ramos, D. G. Free, H. Cohen, D. N. Woodruff, A. L. Thompson and S. J. Clarke, APL Materials, 2015, 3, 041520.