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TT: Tiefe Temperaturen
TT 2: Correlated Electrons - Metal Insulator Transition
TT 2.4: Talk
Friday, March 4, 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 t2g 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.