Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 2: Correlated Electrons - Metal Insulator Transition

TT 2.4: Vortrag

Freitag, 4. März 2005, 11:00–11:15, TU H2053

Electronic gap closure and structural changes in YTiO₃ and LaTiO₃ at high pressures — •Ingo Loa¹, X. Wang¹, K. Syassen¹, M. Hanfland², T. Lorenz³, H. Roth³, and Y.-L. Mathis⁴ — ¹Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart — ²European Synchrotron Radiation Facility, F-38043 Grenoble — ³II. Physikalisches Institut, Universität zu Köln, D-50937 Köln — ⁴Forschungszentrum Karlsruhe, ISS/ANKA, D-76021 Karlsruhe

LaTiO₃ and YTiO₃ are two Mott-Hubbard-type insulators that are characterized by a single 3d electron occupying t_2g orbitals. Both compounds adopt a distorted perovskite-type structure at ambient pressure. We have investigated the pressure-induced changes in the electronic excitation gaps of LaTiO₃ and YTiO₃ by infrared reflection and absorption spectroscopy. These experiments evidence a pressure-induced insulator-to-metal transition in LaTiO₃ near 11 GPa (T=300 K) while YTiO₃ remains insulating to at least 20 GPa. For YTiO₃ we observe a continuous down-shift of the absorption edge from 0.7 eV at ambient conditions to 0.4 eV at 17 GPa. Like in the case of LaTiO₃ this indicates an evolution towards a metallic state at high pressures. The associated structural changes were determined by synchrotron x-ray powder diffraction. We will present detailed information on the equations of state as well as the variations of bond lengths and bond angles as a function of pressure. For YTiO₃ we observe hardly any variation in bond angles with pressure, which makes it attractive as a model system for theoretical investigations.