M. Retuerto, T. Emge, M. R. Li, Z. P. Yin, M. Croft, A. Ignatov, P. W. Stephens, J. Hadermann, J. W. Simonson, M. C. Aronson, A. Pan, D. N. Basov, G. Kotliar, M. Greenblatt
Recently CsTlCl3 and CsTlF3 perovskites were predicted theoretically to be potential superconductors. The synthesis of these two new compounds, together with complete characterizations of the samples is reported for the first time. CsTlCl3 is obtained as orange single crystals and CsTlF3 as light brown powders. The structure of the samples was determined by electron diffraction, synchrotron powder x-ray diffraction and single crystal x-ray diffraction. CsTlCl3 is obtained in two different polymorphs: a tetragonal phase (space group I4/m), similar to CsAuCl3, with Tl1+ and Tl3+ in two different crystallographic positions, and therefore with charge ordering; CsTlCl3 was also obtained as a cubic and less distorted phase (space group Fm-3m), also with two different positions for Tl1+ and Tl3+. CsTlF3 was obtained as a cubic phase with space group Fm-3m and Tl1+ and Tl3+ in two unique sites. All three compounds are paramagnetic; according to theory, hole doping and high pressure are required to achieve superconductivity in the CsTlX3 (X = F, Cl) cubic perovskites. The mixed Tl1+ and Tl3+ valence has been confirmed by x-ray absorption spectroscopy. The optical gap has been determined by spectroscopic techniques to be ~2.5 eV, in reasonable agreement with that calculated by first-principles density functional theory (~2.1 eV). The theoretical design and the experimental validation of CsTlF3 and CsTlCl3 cubic perovskites is an extraordinary starting point since, in theory, superconductivity in these materials can be achieved in cubic phases.
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http://arxiv.org/abs/1302.2353
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