Jeudi 23 février 2012 à 14h00 - salle O. Kahn
Dr. Ayako YAMAMOTO, RIKEN Advanced Science Institute (Japon),
"Synthesis of pyrochlore-type oxides with unusually high valence, Ru5+, Rh4+, and Ir5+, by a high-pressure technique"
It is well known that pyrochlore-type compounds exhibit attractive properties driven by geometrical frustration. Especially, itinerant ones are attractive, because some of them show superconductivity or metal-insulator transition. Here I will present my recent study in synthesis, structure and properties of A2Ru2O7 (A=Hg,Cd,Ca,Tl), Tl2Rh2O7, and A2Ir2O7 (A=Hg,Cd,Ca,Tl). All the compounds are prepared at 4 GPa by a cubic-anvil-type equipment. High-pressure method has advantages in suppressing the vaporization of high- volatile elements, stabilize unusual valence, and keeping oxygen stoichiometry. Most of ruthenium and rhodium oxides show metal-insulator transition or kink, and iridium ones show anomalous metallic feature. I will also present thermal stability of these compounds. The results tell us that each compound stays in delicate balance between cations.