Dr Alessandro Stroppa, Consiglio Nazionale delle Ricerche (CNR), Italy

Dr David Scanlon, University College London

Thursday 7 December 2017
Time: 5pm
Venue: People's Palace room PP2, QMUL, 327 Mile End Road, E1 4NS
Contact: Devis Di Tommaso
Tel: +44 (0)20 7882 6226
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    Dr Alessandro Stroppa
    Electric-Magneto-Optical Kerr Effect in a hybrid organic-inorganic perovskite

    Hybrid organic-inorganic compound attract  a lot of interest for their flexible structures and multifunctional properties.  For example, they can have coexisting magnetism and ferroelectricity who possible coupling give rise to magnetoelectricity.  Here using first-principles computations, we show that, in a perovskite metal-organic framework (MOF), the magnetic and electric orders are further coupled to optical excitations, leading to an Electric tuning of the Magneto-Optical Kerr effect (EMOKE).  Moreover, the Kerr angle can be switched by reversal of both ferroelectric and magnetic polarization only.  The interplay between the Kerr angle and the organic-inorganic components of MOFs offers surprising unprecedented tools for engineering MOKE in complex compounds.  Note that this work may be relevant to acentric magnetic systems in general, e.g., multiferroics.

    A. Stroppa et al. J. Am. Chem. Soc., 2017,139 (37), pp 12883-12886

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    Dr David Scanlon
    Designing Earth Abundant Transparent Oxides for Energy Generation

    The combination of transparency to visible light (optical band gaps in excess of 3.1 eV) and high electrical conductivity (conductivities > 103 S/cm) in a metal oxide material is quite unusual as these are normally mutually exclusive properties.[1] This combination has been realised, however, for a small subset of metal oxides, termed transparent conducting oxides (TCOs), such as ZnO, CdO, Ga2O3, SnO2, In2O3, BaSnO3 etc.[2-5] The cationic species in these materials are all “post transition metals” and so all possesses a (n–1)d10ns0np0 electronic structure. The hybridization between the cations s states and the O p states typically yield low lying conduction band minima (high electron affinities) with excellent conduction band dispersion (low effective masses – high electron mobility).[6] Another cation which possesses an (n–1)d10ns0np0 electronic structure is Sb(V), however, oxides featuring Sb(V) have not enjoyed a huge amount of study to date.

    Recently, however, ZnSb2O6 has been identified from a high throughput computational screening to have an electronic structure that could be ideal for TCO applications.[7] There is some experimental support for this as crystalline samples of ZnSb2O6 formed from sintered powder were reported to demonstrate some n-type conductivity in 2005,[8] although not to the level necessary for TCO applications. It should be noted, however, that the best TCOs (e.g. BaSnO3) only show high performance when doped with a suitable electron donor. In this presentation, we outline a hybrid density functional theory examination of the defect chemistry of ZnSb2O6, including intrinsic defects and extrinsic donors. Our calculations have allowed us to identify the ideal dopants for ZnSb2O6, demonstrating its suitability as a next generation n-type TCO. In addition, we also demonstrate that ZnSb2O6 shows great promise as an oxide thermoelectric material at high temperature.

    Adam J. Jackson1,2, Alex M. Ganose1,2,3, Benjamin A. D. Williamson,1,2 R. H. Kalra,1,2 and David O. Scanlon1,2,3,* 1University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, UK; 2Thomas Young Centre, University College London, Gower Street, London WC1E 6BT, UK 3Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK

    [1] P. D. C. King and T. D. Veal, J. Phys.: Condens. Matter, 23, 334214 (2011) [2] M. Burbano, D. O. Scanlon, and G. W. Watson, J. Am. Chem. Soc. 133, 15065 (2011).

    [3] D. O. Scanlon and G.W. Watson, J. Mater. Chem. 22, 25236 (2012) [4] A. Walsh  et al., Phys. Rev. Lett. 100, 167402 (2008) [5] Z. Leben-Higgins et al., Phys. Rev. Lett., 116, 027602 (2016) [6] H. Mizoguchi and P. M. Woodward, Chem. Mater, 16, 5233 (2004) [7] G. Hautier et al., Chem, Mater, 26, 5447 (2014) [8] N. Kikuchi et al. J. Am. Ceram. Soc., 88, 2793 (2005)


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