Abstract
A new member of the CaCu 3 B 2 B' 2 O 12 perovskite family, CaCu 3 Cr 2 Ru 2 O 12 , has been synthesized at 12 GPa and 1150 °C. Rietveld refinement using powder X-ray diffraction data reveals that this oxide crystallizes in space group Im3 where cations are disordered over the octahedral B site. Measurements of magnetic susceptibility exhibit a temperature independent Pauli paramagnetic behavior. There is no indication of magnetic ordering, in contrast to the ferrimagnetic behavior associated with the superexchange between Cu(II) and Cr(III) in CaCu 3 Cr 2 Sb 2 O 12 . Although itinerant electron behavior is similar to that observed for the isostructural CaCu 3 Ga 2 Ru 2 O 12 , Cu(II)-O-Ru(V) ↔ Cu(III)-O-Ru(IV) charge transfer is not expected. Rather, a delocalization mechanism involving both CrO 6 and RuO 6 octahedral sublattices is proposed, as is typical for double perovskites. The pure paramagnetic behaviors of CaCu 3 Ga 2 B' 2 O 12 (B' = Nb, Sb, and Ta) perovskites, which contrast with the antiferromagnetic CaCu 3 Ti 4 O 12 , indicate that the electronic coupling within the A sublattice is strongly influenced by the electronic structure of the B sublattice.
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