New perovskite oxide CaCu ₃Cr ₂Ru ₂O ₁₂: Comparison with structural, magnetic, and transport properties of the CaCu ₃B ₂B′ ₂O ₁₂ perovskite family

A new member of the CaCu ₃B ₂B′ ₂O ₁₂ perovskite family, CaCu ₃Cr ₂Ru ₂O 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 Im3̄ 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(in) in CaCu ₃Cr ₂Sb ₂O ₁₂. Although itinerant electron behavior is similar to that observed for the isostructural CaCu ₃Ga ₂Ru ₂O 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 ₃Ga ₂B′ ₂O ₁₂ (B′ = Nb, Sb, and Ta) perovskites, which contrast with the antiferromagnetic CaCu ₃Ti ₄O ₁₂, indicate that the electronic coupling within the A sublattice is strongly influenced by the electronic structure of the B sublattice.