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arXiv · 0806.2396

Mott-Hubbard gap closure and structural phase transition in the oxyhalides TiOBr and TiOCl under pressure

C. A. Kuntscher·A. Pashkin·H. Hoffmann·S. Frank·M. Klemm·S. Horn·A. Schönleber·S. van Smaalen·M. Hanfland·S. Glawion·M. Sing·R. Claessen
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Abstract

Pressure-dependent transmittance and reflectance spectra of TiOBr and TiOCl single crystals at room temperature suggest the closure of the Mott-Hubbard gap, i.e., the gap is filled with additional electronic states extending down to the far-infrared range. According to pressure-dependent x-ray powder diffraction data the gap closure coincides with a structural phase transition. The transition in TiOBr occurs at slightly lower pressure ($p$=14 GPa) compared to TiOCl ($p$=16 GPa) under hydrostatic conditions, which is discussed in terms of the chemical pressure effect. The results of pressure-dependent transmittance measurements on TiOBr at low temperatures reveal similar effects at 23 K, where the compound is in the spin-Peierls phase at ambient pressure.

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C. A. Kuntscher, A. Pashkin, H. Hoffmann, S. Frank, M. Klemm, S. Horn, A. Schönleber, S. van Smaalen, M. Hanfland, S. Glawion, M. Sing, R. Claessen. 2008-06-14. Mott-Hubbard gap closure and structural phase transition in the oxyhalides TiOBr and TiOCl under pressure. https://doi.org/10.1103/physrevb.78.035106

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