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Hole Doping and Structural Transformation in CsTl1–xHgxCl3

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posted on 02.02.2015, 00:00 by Maria Retuerto, Zhiping Yin, Thomas J. Emge, Peter W. Stephens, Man-Rong Li, Tapati Sarkar, Mark C. Croft, Alexander Ignatov, Z. Yuan, S. J. Zhang, Changqing Jin, Robert Paria Sena, Joke Hadermann, Gabriel Kotliar, Martha Greenblatt
CsTlCl3 and CsTlF3 perovskites have been theoretically predicted to be superconductors when properly hole-doped. Both compounds have been previously prepared as pure compounds: CsTlCl3 in a tetragonal (I4/m) and a cubic (Fmm) perovskite polymorph and CsTlF3 as a cubic perovskite (Fmm). In this work, substitution of Tl in CsTlCl3 with Hg is reported, in an attempt to hole-dope the system and induce superconductivity. The whole series CsTl1–xHgxCl3 (x = 0.0, 0.1, 0.2, 0.4, 0.6, and 0.8) was prepared. CsTl0.9Hg0.1Cl3 is tetragonal as the more stable phase of CsTlCl3. However, CsTl0.8Hg0.2Cl3 is already cubic with the space group Fmm and with two different positions for Tl+ and Tl3+. For x = 0.4 and 0.5, solid solutions could not be formed. For x ≥ 0.6, the samples are primitive cubic perovskites with one crystallographic position for Tl+, Tl3+, and Hg2+. All of the samples formed are insulating, and there is no signature of superconductivity. X-ray absorption spectroscopy indicates that all of the samples have a mixed-valence state of Tl+ and Tl3+. Raman spectroscopy shows the presence of the active Tl–Cl–Tl stretching mode over the whole series and the intensity of the Tl–Cl–Hg mode increases with increasing Hg content. First-principle calculations confirmed that the phases are insulators in their ground state and that Hg is not a good dopant in the search for superconductivity in this system.

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