Multiple-phase evolution and electrical transport of Sr 4- x Y x Co 4 O 12- δ ( x = 0-1.0): an ordered phase transition process.

The transition metal oxide (TMO) SrCoO 3- 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 Sr 4- x Y x Co 4 O 12- δ ( x = 0-1.0) ceramics. Sr 6 Co 5 O 15 ( x = 0) adopts a hexagonal structure (H), Sr 4- x Y x Co 4 O 12- δ ( x = 0.2-0.4) ceramics adopts a cubic perovskite (CP) structure, and Sr 4- x Y x Co 4 O 10.5+ 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 Sr 3 YCo 4 O 10.5 ( 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 Sr 4- x Y x Co 4 O 12- 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 Sr 4- x Y x Co 4 O 12- δ ( x = 0-1.0) ceramics show semiconductive electrical transport behavior. Sr 6 Co 5 O 15 (H) with a one-dimensional chain structure has the highest resistivity, while Sr 3.8 Y 0.2 Co 4 O 12- δ (CP) with a three-dimensional corner-sharing structure exhibits the lowest resistivity, and Sr 4- x Y x Co 4 O 12- δ ( x = 0.2-1.0) ceramics show an increasing tendency in resistivity due to the hole carrier Co 4+ converting to Co 3+ . We studied multiple-phase evolution and ordered phase transition in Sr 4- x Y x Co 4 O 12- δ ( x = 0-1.0) ceramics through Y-O bonding.