Structure and magnetism of rare-earth-substituted Ca3Co2O6

Yttrium- and rare-earth-substituted derivatives of Ca3−vRvCo2O6 (R6-point double bond; length half of m-dashY, 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-type structure with space group R3¯c), in which the trivalent R3+ substituents randomly occupy the Ca2+ site. The homogeneity range of Ca3−vRvCo2O6 extends to v≈0.90 for the substituents concerned. A significant increase in the Co2–O distances within the trigonal-prismatic Co2O6 co-ordination 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>∼0.30.