Electronic phase diagram of Li_xCoO_2 revisited with potentiostatically deintercalated single crystals

摘要

Electronic phase diagram of Li_xCoO_2 has been reexamined using potentiostatically de-intercalated single-crystal samples. Stable phases of x ～ 0.87, 0.72, 0.53, 0.50, 0.43, and 0.33 were found and isolated for physical property studies. A-type and chain-type antiferromagnetic orderings have been suggested from magnetic susceptibility measurement results in x ～ 0.87 and 0.50 below approximately 10 and 200 K, respectively, similar to those found in Na_xCoO_2 system. There is no Li vacancy superlattice ordering observed at room temperature for the electronically stable phase Li_(0.72)CoO_2 as revealed by synchrotron x-ray Laue diffraction. The peculiar magnetic anomaly near ～175 K as often found in powder samples of x ～ 0.46-0.78 cannot be isolated through this single-crystal potentiostatic method, which supports the previously proposed explanation to be a surface stabilized phase of significant thermal hysteresis and aging character.