Structure and physical properties of layered double perovskite NdBaCo2O5.50 + δ (δ ≈ 0.25)

Magnetic, electric, and elastic properties of the crystal and magnetic structure of double layered perovskite NdBaCo₂O_{5.50 + δ} are studied by the neutron diffraction method at various temperatures. The data are analyzed using two models of crystal structure. In the first model, the sample consists of two crystal-structure phases with ordered and disordered arrangements of oxygen vacancies. In the second model, a new crystal-structure phase is formed in this compound, which is characterized by ordering of oxygen vacancies in the plane of the rare-earth ion in the 1c crystallographic position (0, 0, 1/2) of space group Pmmm. Two crystal-structure models correspond to different types of magnetic ordering (a mixture of a ferromagnetic phase and a G-type antiferromagnetic phase is presumed in the two-phase crystal-structure model, while a canted antiferromagnetic structure is presumed in the one-phase crystal structure model). The behavior of electric and elastic parameters is better described in the first model, while neutron diffraction studies are in better agreement with the second model.