Dresden 2006 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 25: Correlated Electrons - Poster Session

TT 25.117: Poster

Mittwoch, 29. März 2006, 14:30–18:30, P1

Temperature- and doping-induced spin-state transitions of RCoO₃ — •K. Berggold, N. Hollmann, M. Reuther, M. Kriener, J. Baier, C. Zobel, A. Reichl, and T. Lorenz — II. Physikalisches Institut, University of Cologne, Germany

LaCoO₃ attracts a lot of attention, because it undergoes a temperature-induced spin-state transition. There are different ways to tune this spin-state transition, either to stabilize the low-spin state by replacing La with smaller rare earth ions R, or to suppress it by the introduction of charge-carriers[1,2]. For low doping levels so-called high-spin polarons are formed. We studied the thermal conductivity κ on RCoO₃ single crystals with R = La, Pr, Nd, and Eu, as well as on La_1−xSr_xCoO₃ with 0≤ x≤0.3 and find that κ is strongly suppressed by the spin-state transition. Particularly we present magnetic-field dependent measurements for low temperatures to investigate the influence of the high-spin polarons to κ. A low thermal conductivity is one pre-condition to reach large values of the thermoelectric figure of merit ZT, which is necessary for thermoelectric applications. We observe a ZT^(max)≈0.03, which is rather high for oxides[3]. We also present first measurements of Eu_1−xSr_xCoO₃. Here, charge-carrier doping should act differently because of the stabilized low-spin state.

[1] Baier et al., PRB 72, 155116 (2005)

[2] Kriener et al.,PRB 69, 094417 (2004)

[3] Berggold et al.,PRB 71, 014443 (2005)

This work was supported by the DFG through SFB 608