Orientational Phase Transition Around 274 K in C_60 Single Crystal

• 作 者: 徐亚伯 何丕模 杨宏顺 郑萍 余朝文 陈兆甲 张宣嘉 李文铸
• 机 构: Department of Physics,Zhejiang University,Hangzhou 310027,PRC,Department of Physics,Zhejiang Univers
• 出 处: Science in China,Ser.A
• 发表日期: 1994年11期
• 关键词: rotation disordered Transition symmetry delta conclusion dimensions beginning sh

The electrical conductivity of a C60 single crystal around 274 K and the specific heat of C60 crystals from 150 to 340 K have been measured.The delta-like specific heat peak at about 251 K related to the first-order phase transition has been reported.The activation energy change around 274 K and the lambda-like specific heat peak beginning at 270 K and ending at 310 K show that there is an orientational phase transition in fcc C60 crystals above 251 K.By taking the symmetry into consideration and further analyzing lambda-like specific heat peak and the activation energy change around 274 K,the conclusion has been reached that this new phase transition is an orientational structure transition from the merohedral twinning fcc to the orientationally disordered fcc.The temperature of free rotation of C60 molecules is about 281 K.

The electrical conductivity of a C60 single crystal around 274 K and the specific heat of C60 crystals from 150 to 340 K has been measured. The delta-like specific heat peak at about 251 K related to the first-order phase transition has been reported. The activation energy change around 274 K and the lambda-like specific heat peak beginning at 270 K and ending at 310 K show that there is an orientational phase transition in fcc C60 crystals above 251 K. By taking the symmetry into consideration and further analyzing lambda -like specific heat peak and the activation energy change around 274 K, the conclusion has been reached that this new phase transition is an orientational structure transition from the merohedral twinning fcc to the orientally disordered fcc. temperature of free rotation of C60 molecules is about 281 K.