  RbOs2O6, the third superconducting pyrochlore oxide (known so far), has been
synthesized by encapsulation and by high pressure techniques. Suitable post
chemical treatment of the as-prepared sample allowed us to eliminate the
impurity phases. Bulk superconductivity with Tc=6.4 K was observed in
magnetisation and specific heat measurements. The transition temperature of
RbOs2O6 was found to be the same for both preparation methods. Structural
investigations showed that Rb atoms occupy the 8b site in the pyrochlore
lattice with a lattice parameter of 10.1137(1) A.
