Hamburg 2001 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 25: Postersitzung III: Pinning und Vortexdynamik, Massive HTSL, Bandleiter, Transporteigenschaften in HTSL, SL dünner Filme, Elektronen und Phononen in HTSL, Tunneln, Borkarbide, Quantenphasen und Metall-Isolator-Überg
änge, Anwendungen, Sonstiges

TT 25.45: Poster

Donnerstag, 29. März 2001, 14:30–17:00, Rang S\ 3

The Low Temperature States of Germanium Clathrates — •H. Q. Yuan, S. Paschen, M. Grosche, W. Carrillo-Cabrera, C. Langhammer, G. Sparn, Y. Grin, M. Baenitz, and F. Steglich — MPI-CPfS, Nöthnitzer Str. 40, 01187 Dresden

The newly discovered Ba₆Ge₂₅ belongs to the chiral clathrate structure family CP124. In this compound, Germanium atoms are located at the vertices of condensed pentagondodecahedra. Each of the pentagondodecahedra is centered by one Barium atom and the remaining Barium atoms occupy the cavities created by the dense-piling of the pentagondodecahedra. In this poster, we present the novel low temperature states of the clathrate Ba₆Ge₂₅ and its related compounds by tuning the materials with hydrostatic pressure. At ambient pressure, Ba₆Ge₂₅ shows a two-step structural phase transition between 170K and 230K and a superconducting transition at T_c≈0.24K. With increasing pressure, the high temperature transitions are suppressed and disappear at a critical pressure of about

27kbar, while T_c increases dramatically and reaches a maximum value of 4K near p_c. On replacing 1/3 of the Ba atoms with Na, no

structural phase transitions are observed at ambient pressure and the system displays a metallic resistivity above the superconducting transition which decreases with increasing pressure.