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Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 2: Correlated Electrons - Metal Insulator Transition

TT 2.11: Talk

Friday, March 4, 2005, 12:45–13:00, TU H2053

Effect of pressure on the electric transport properties of RNiO3 — •R. Lengsdorf1, J.A. Alonso2, D.I. Khomskii1, H. Micklitz1, and M.M. Abd-Elmeguid11II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln — 2Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid, Spain

The temperature-induced metal-insulator (MI) transition in the RNiO3 series has been ascribed to an opening of a small charge transfer gap at T<TMI which is intimately connected with either a slight but abrupt expansion of the unit cell volume or an orthorhombic (Pbnm) to monoclinic (P21/n) structural transition for large (R=Pr,.., Eu) and small (R=Dy,.., Lu) R3+ ions, respectively. The monoclinic symmetry in the insulating state implies two independent Ni-sites and the presence of charge ordering. Experimental evidence for such a charge ordered state in larger R3+ nickelates has recently been reported (e.g. EuNiO3 and NdNiO3 thin films), supporting the importance of charge ordering for the occurence of the temperature-induced MI transition. For a deeper understanding of the mechanism of the MI transition in the RNiO3 series, we have studied the effect of pressure on the transport properties of some selected RNiO3 (R=Sm, Eu, Y and Lu) oxides. While the monoclinic structure of YNiO3 (TMI=582 K and TN=138 K) and LuNiO3 (TMI=599 K and TN=125 K) remains stable up to 14 GPa and 16 GPa, respectively, the pressure-temperature dependence of the electrical resistance clearly indicates a transition to a metallic state already at p≥5 GPa. Possible mechanisms responsible for the pressure-induced insulator-metal transition in RNiO3 series will be discussed.

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