We have measured the susceptibility, specific heat, resistivity, and thermopower of CaCu3Ti4-xRuxO12 and CaCu3-yMnyRu4O12, and have found that CaCu3Ru4O12 can be regarded as a heavy-fermion oxide in d-electron systems. The Kondo temperature is near 200 K, and the susceptibility (1.4 × 10-3 cmu/ Cu mol) and the electron specific heat coefficient [28 mJ/(Cu mol K2)] are moderately enhanced. The resistivity is proportional to T2 at low temperatures, and satisfies the Kadowaki-Woods relation. The heavy-fermion state comes from the interaction between the localized moment of Cu 3d and the conduction electron of Ru 4d. An insulator-metal transition occurs between x = 1.5 and 4 in CaCu3-Ti4-xRuxO12, which can be regarded as a transition from a magnetic insulator to a heavy-fermion metal.
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