On the existence of a homologous series of BamCum+nOy oxides with the cubic structure of the BaCuO2 oxide

Phase relations have been studied in the BaO–CuO_x system in the range of 42.0–83.0 mol.% CuO at P(O₂) = 21 kPa (air) by visual polythermal analysis (VPA), powder X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), chemical analysis (CA), and electron diffraction (ED) with simultaneous elemental analysis (EA) in a transmission electron microscope (TEM). The existence of discrete crystallization fields of barium–copper oxides of cation compositions Ba₄Cu₅O_y, Ba₅Cu₆O_y, Ba₇Cu₈O_y, Ba₁₂Cu₁₃O_y, and Ba₂₄Cu₂₅O_y, which have the cubic structure of the BaCuO₂ oxide, is revealed in the studied region of the system. The oxides may be represented as members of a Ba_mCu_m+nO_y homologous series. The BaCuO₂ oxide does not exist in the subsolidus region and does not have its own crystallization field. The oxygen-deficient oxide BaCuO_1.78 of the cation composition (Ba:Cu) 1:1 with the BaCuO₂ cubic structure is found in melted samples of the 50.0 mol.% CuO composition quenched at 1020–1060 °С.