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

The entire family of carefully oxygen-adjusted RBaCo₂O_5.5 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.