Crystal growth features and properties of layered rare earth and barium cobaltates

High quality single crystals of LnBaCo₂O_5+δ (0 < δ < 1) (Ln = Pr, Eu, Gd, Tb, Dy) with rectangular shape and average dimensions 5 mm × 5 mm × 1 mm were grown for the first time from overstoichiometric flux melt. The data on the primary crystallization field of most cobaltate phases, which appear in parts of corresponding Gibbs triangles in the range 1373 - 1523 K are discussed. Bulk single crystals of new phases HoBaCo₄O₇ up to 300 mm³, YBaCo ₄O₇ and TbBaCo₄O₇ up to 10 mm ³ in volume were grown first. A solution of these compounds structure has been found in the space group P6₃mc. For the Ln = Pr, Gd, Sm, Tb, Dy, Ho based systems under the liquidus line there are several other new cobaltate phases of both perovskite, and hexagonal crystal structure. Stability of the double perovskite phase and temperature of the antiferromagnetic - ferromagnetic phase transition in relation to the radius of rare earth ions are compared. The data on the exact analysis of chemical composition, including EDX and iodometric titration, as well as results on magnetic susceptibility of EuBaCo_1-xAl_xO_5+δ (0 < x < 0.3) are discussed.