Structural Phase Transition from Rhombohedral to Cubic in LaCoO3.

摘要: Lanthanum cobalt oxide LaCoO3 has a rhombohedrally distorted perovskite structure with the crystal space group of R3c.1-3) Raccah and Goodenough have reported that varies increasing temperature from R3c to R3 around K. In high phase, two kinds inequivalent Co atoms order preferentially on alternate (111) 2) They also first insulator-to-metal phase transition at 1210K accompanied an abrupt drop rhombohedral angle 60.4◦ 60◦ keeping symmetry through transition. addition, they endothermic 1210K, higher transitions 550 900K differential thermal analysis. A powder neutron diffraction study revealed between 4.2 1248K, possible exception 668K. According study, remains 60.3◦ even 1248K. Their does not support 1210K. investigate structural LaCoO3, we performed X-ray measurement, thermogravimetric (TG) analysis (DTA) temperatures. The results suggest second crystallographic cubic 1610K, show any anomaly previously is intrinsic one in pure LaCoO3. samples for measurements were obtained single grown lamp-image floating zone furnace. using high-accuracy diffractometer equipped parabolic multilayer parallel slit analyzer 300 1700K air atmosphere. (TG-DTA) was 1773K both crystalline bulk polycrystalline TG-DTA (Rigaku TG-8120D) coupled mass spectrometer (Q-MS, Rigaku Thermo-Mass QA550