Synthesis, structure, oxygen content and properties of layered Dy 1.2 Ba 1.8 Fe 1.8 Co 1.2 O 8‐δ

It is shown that an excess of Dy in A‐site (in amount of 0.2 in formula units) allows synthesizing a single‐phase perovskite‐related oxide with the 123‐type structure at 1100 °C in air. Cobalt ions completely fill the octahedrally coordinated positions in the structure of 123‐type Dy 1.2 Ba 1.8 Fe 1.8 Co 1.2 O 8‐δ , while iron together with excess Co is in the pyramidal oxygen coordination. The oxygen content at room temperature of 7.86 decreases with temperature. A slight increase in the slope of thermal expansion observed at T >200 °C. The electrical conductivity, carried out mainly by holes, increases non‐linearly with temperature, reaching a maximum value 14.8 S ⋅ cm −1 at 900 °C. Magnetic measurements allow assuming that Fe 3+ are in low spin state, all Co 2+ ions are in high spin, and Co 3+ can be split into several states depending on coordination.