Multiple-phase evolution and electrical transport of Sr4−xYxCo4O12−δ (x = 0–1.0): an ordered phase transition process. Issue 14 (14th March 2023) - Song, Hongyuan
Abstract : Controllable synthesis of multiphase perovskites Sr4− x Y x Co4 O12− δ and an ordered tetragonal phase transition process with contribution of the Y–O bond. Abstract : 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− x Y x Co4 O12− δ ( x = 0–1.0) ceramics. Sr6 Co5 O15 ( x = 0) adopts a hexagonal structure (H), Sr4− x Y x Co4 O12− δ ( x = 0.2–0.4) ceramics adopts a cubic perovskite (CP) structure, and Sr4− x Y x Co4 O10.5+ 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 Sr3 YCo4 O10.5 ( 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− x Y x Co4 O12− 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− x Y x Co4 O12− δ ( x = 0–1.0) ceramics show semiconductive electrical transport behavior. Sr6 Co5 O15 (H) with a one-dimensional chain structure has the highest resistivity, while Sr3.8 Y0.2 Co4 O12− δ (CP) with a three-dimensional corner-sharing structure exhibits the lowest resistivity, and Sr4− x Y x Co4 O12− 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 Sr4− x Y x Co4 O12− δ ( x = 0–1.0) ceramics through Y–O bonding.