Multiple-phase evolution and electrical transport of Sr4−xYxCo4O12−δ (x = 0–1.0): an ordered phase transition process

The transition metal oxide (TMO) SrCoO3−δ family with rich structural diversity has been widely studied in the phase transition and energy application fields. We report the multiple-phase structure evolution, phase transitions during sintering, and electrical transport of A-site doped Sr4−xYxCo4O12−δ (x = 0–1.0) ceramics. Sr6Co5O15 (x = 0) adopts a hexagonal structure (H), Sr4−xYxCo4O12−δ (x = 0.2–0.4) ceramics adopts a cubic perovskite (CP) structure, and Sr4−xYxCo4O10.5+δ′ (x = 0.8–1.0) ceramics adopts an ordered-tetragonal (OT) structure; moreover, their phase transitions during the sintering processing of samples are systematically investigated. Combining the thermal analysis and X-ray diffraction results, the exothermic peak and weight gain of Sr3YCo4O10.5 (x = 1.0, T) at 1042 °C are considered to correspond to an ordered phase transition (T → OT) occurring. Finally, a systematic phase schema of the Sr4−xYxCo4O12−δ (x = 0–1.0) state dependence on the Y content and sintering temperature is obtained. The high-energy Y–O bond stabilizes the high-temperature CP structure (x = 0.2–0.4) and induces a structural evolution from the CP to OT structure (x = 0.8–1.0). In addition, all Sr4−xYxCo4O12−δ (x = 0–1.0) ceramics show semiconductive electrical transport behavior. Sr6Co5O15 (H) with a one-dimensional chain structure has the highest resistivity, while Sr3.8Y0.2Co4O12−δ (CP) with a three-dimensional corner-sharing structure exhibits the lowest resistivity, and Sr4−xYxCo4O12−δ (x = 0.2–1.0) ceramics show an increasing tendency in resistivity due to the hole carrier Co4+ converting to Co3+. We studied multiple-phase evolution and ordered phase transition in Sr4−xYxCo4O12−δ (x = 0–1.0) ceramics through Y–O bonding.