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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
Thursday, March 29, 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 Tc≈0.24K. With increasing pressure, the high temperature transitions are suppressed and disappear at a critical pressure of about
27kbar, while Tc increases dramatically and reaches a maximum value of 4K near pc. 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.