R-site varied series of RBaCo2O5.5 (R2Ba2Co4O11) compounds with precisely controlled oxygen content

The entire family of carefully oxygen-adjusted RBaCo2O5.5 or R2Ba2Co4O11 (R=Y, Ho–La) double-perovskite oxides is systematically investigated for the lattice parameters, A-site cation disorder, and characteristic physical properties, i.e. the metal–insulator transition, ferromagnetic transition and so-called metamagnetic transition. With increasing size of the R constituent, the lattice parameters start to deviate from the linear behavior, indicating partial oxygen/vacancy and A-site cation disorder for the largest Rs of Nd, Pr and La. Both the metal–insulator transition and the two magnetic transitions are found to be highly sensitive to even minor deviations from the ideal 5.5 oxygen stoichiometry, thus underlining the importance of proper oxygen-content adjustment.