Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.76: Poster

Samstag, 5. März 2005, 11:00–16:30, Poster TU C

Low temperature mixed spin state of Co³⁺ in LaCoO₃ evidenced from local lattice distortions — •V. Gnezdilov¹, P. Lemmens^2,3, Yu.G. Pashkevich⁴, K.-Y. Choi⁵, S. Shiry aev⁶, G. Bychkov⁶, and S. Barilo⁶ — ¹B.I. Verkin Inst. for Low Temp. Physics NASU, 61164 Kharkov, Ukraine — ²Inst. for Physics of Condensed Matter, TU Braunschweig, D-38106 Braunschweig, Germany — ³MPI-FKF, D-70569 Stuttgart, Germany — ⁴A.A. Galkin Donetsk Phystech NASU, 83114 Donetsk, Ukraine — ⁵Inst. for Materials Research, Tohoku University, Sendai 980-8577, Japan — ⁶Inst. of Physics of Solids & Semiconductors, Academy of Sciences, 220072 Minsk, Belarus

Single- and multi-phonon excitations of the single crystalline LaCoO₃ were studied using Raman spectroscopy in the temperature region of 5 K - 300 K. First-order Raman spectra show a larger number of phonon modes than allowed for the rhombohedral (D_3d⁶) structure. Additional phonon modes are interpreted in terms of activated modes due to local lattice distortions arising from the Jahn-Teller (JT) activity of the intermediate-spin (IS) state of Co³⁺ ions. The temperature dependence of the breathing - and stretching-type phonon modes on cooling suggests the presence of Co³⁺ ions in the intermediate spin state, even at lowest temperatures. The anomalous temperature dependence of the second-order phonon excitations spectra is in accordance with the Franck-Condon mechanism that is characteristic for a JT orbital order.