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We synthesized ACu3Ru4O12 (A = Na, Na0.5Ca0.5, Ca, Ca0.5La0.5, La) andmeasured their DC magnetization, AC susceptibility, specific heat, andresistivity, in order to investigate the effects of the hetero-valentsubstitution. A broad peak in the DC magnetization around 200 K was observedonly in CaCu3Ru4O12, suggesting the Kondo effect due to localized Cu2+ ions.However, the electronic specific heat coefficients exhibit large values notonly for CaCu3Ru4O12 but also for all the other samples. Moreover, the Wilsonratio and the Kadowaki-Woods ratio of our samples are all similar to the valuesof other heavy-fermion compounds. These results question the Kondo effect asthe dominant origin of the mass enhancement, and rather indicate the importanceof correlations among itinerant Ru electrons.

Heavy-Mass Behavior of Ordered Perovskites ACu3Ru4O12 (A = Na, Ca, La)