Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 27: Solids at Low Temperature - New Materials

TT 27.2: Talk

Tuesday, March 8, 2005, 12:15–12:30, TU H3027

Influence of structural distortions on electronic properties of Ba₆Ge₂₅ clathrate — •Ivica Zerec¹, Wilder Carrillo-Cabrera¹, Vladimir Voevodin¹, Jörg Sichelschmidt¹, Alexander Yaresko², Peter Thalmeier¹, and Yuri Grin¹ — ¹Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden — ²Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, 01187 Dresden

Clathrates are cage compounds, recently investigated as interesting candidates for thermoelectric applications. The complex structure poses a major challenge in understanding the variety of their interesting physical properties. We present the electronic band structure calculations for Ba₆Ge₂₅ clathrate. It undergoes an involved structural phase transition, accompanied with stepwise changes of many physical quantities. We construct the ordered structural models for different temperatures, in accordance with the experimental data and calculate the corresponding electronic band structures. We show how the changes of electronic properties across the phase transition may be understood from the modifications of the band structure induced by the structural distortions. In particular we show how the shift of the optical spectral weights towards higher frequencies, observed in the optical conductivity below the phase transition, is well reproduced by the theoretical calculations based on the electronic band structure.