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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 Dy1.2Ba1.8Fe1.8Co1.2O8‐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 Fe3+ are in low spin state, all Co2+ ions are in high spin, and Co3+ can be split into several states depending on coordination. [ABSTRACT FROM AUTHOR]

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 Dy1.2Ba1.8Fe1.8Co1.2O8‐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 Fe3+ are in low spin state, all Co2+ ions are in high spin, and Co3+ can be split into several states depending on coordination. [ABSTRACT FROM AUTHOR]