La₂₆Ge₁₉M₅O₅ (M = Ag, Cu): New superconductors with diverse cluster-based structures

The discovery of unusual chemical bonding in La₂₆Ge₁₉M₅O₅ (M = Ag, Cu) provides another path for discovering new superconductors with diverse cluster-based structures that can also possess interesting chemical and physical properties. La₂₆Ge₁₉M₅O₅ (M = Ag, Cu) are isostructural superconductors with onset T_cs of 5.4 K and 6.4 K, respectively, based on resistance and magnetization measurements. High-pressure magnetization measurements were also conducted up to 1.26 GPa in a piston-cylinder-type high-pressure cell compatible with the MPMS3. The T_c of each compound increased with increasing pressure, with no sign of saturation. The Ag and Cu transition temperatures increased by 26% and 13%, respectively. The study presented here not only supports our previous work on BaNaTiSbO, but may lead to the pursuit of new compounds in rare-earth-metal/transition-metal/main-group-metal suboxides.