Structure and magnetism of rare-earth-substituted Ca3Co2O6

Yttrium- and rare-earth-substituted derivatives of Ca3-vRvCo2O6 (R=Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Lu) have been synthesized and structurally characterized by powder X-ray and neutron diffraction. All phases adopt the K4CdCl6-tYPC structure with space group R (3) over barc), in which the trivalent R3+ substituents randomly occupy the Ca2+ site. The homogeneity range of Ca3-vRvCo2O6 extends to v approximate to 0.90 for the substituents concerned. A significant increase in the Co2-O distances within the trigonal-prismatic Co2O(6) coordination polyhedra upon introduction of R3+ confirms that extra electrons from the R3+ -for-Ca2+ substitution exclusively enter the Co2 site of the quasi-one-dimensional Ca3-vRvCo2O6 structure, thereby formally reducing its oxidation state. This is furthermore supported by magnetic susceptibility and low-temperature neutron diffraction measurements. The long-range ferrimagnetic ordering temperature is reduced upon R substitution and appears to vanish for v >similar to 0.30. (c) 2006 Elsevier Inc. All rights reserved.