Understanding the complexities of electronic and magnetic ground states in
solids is one of the main goals of solid-state physics. Transition-metal ox
ides have proved to be particularly fruitful in this regard, especially for
those materials with the perovskite structure, where the special character
istics of transition-metal-oxygen orbital hybridization determine their pro
perties. Ruthenates have recently emerged as an important family of perovsk
ites because of the unexpected evolution from high-temperature ferromagneti
sm in SrRuO3 to low-temperature superconductivity in Sr2RuO4 (refs 1, 2). H
ere we show that a ruthenate in a different structural family, La4Ru6O19, d
isplays a number of highly unusual properties, most notably non-Fermi-liqui
d behaviour. The properties of La4Ru6O19 have no analogy among the thousand
s of previously characterized transition-metal oxides. Instead, they resemb
le those of CeCu6-xAux-a widely studied f-electron-based heavy fermion inte
rmetallic compound that is often considered as providing the best example o
f non-Fermi-liquid behaviour. In the ruthenate, non-Fermi-liquid behaviour
appears to arise from just the right balance between the interactions of lo
calized electronic states derived from Ru-Ru bonding and delocalized states
derived from Ru-O hybridization.