K_3C_(60)在200K附近的取向相变机理  

MECHANISM FOR THE ORIENTATIONAL PHASE TRANSITION OF K_3C_(60)

作　　者：李宏年[1] 徐亚伯[1] 鲍世宁[1] 李海洋[1] 吴太权[1] 陈晓[1] 钱海杰[2] 易.奎热西 刘风琴[2] 

机构地区：[1]浙江大学物理系 [2]中国科学院高能物理研究所国家同步辐射实验室,北京100039

出　　处：《物理学报》2001年第12期2456-2460,共5页Acta Physica Sinica

基　　金：国家自然科学基金 (批准号 :10 0 740 5 3 );浙江省自然科学基金 (批准号 :10 0 0 19);浙江省教育厅资助的课题~~

摘　　要：研究了K3C6 0 单晶薄膜在 2 0 0K附近的导带结构 .样品温度为 190K时 ,同步辐射角分辨光电子谱能够观察到[111]方向有规律的能带色散 .而在 2 2 0K附近色散不存在 .这一实验结果与K3C6 0 在 2 0 0K存在取向相变相符合 .用反铁磁Ising模型对实验结果进行了分析 .结果表明 ,K3C6 0 在 2 0 0K的相变是由低温下的一维无序取向结构转变为2 0 0K以上的双取向结构畴与无序分子 (约占 40 % )Conduction band structure of K3C60 single crystal films was studied at temperatures near 200 K. Band dispersions along the [111] direction could be observed at 190 K using synchrotron radiation photoemission spectra technique. When the sample temperature increased to 220 K, most subpeaks of the conduction band vanished and the dispersions could not be observed. This result coincides with the existence of an orientational phase transition occurring at 200 K. The fcc nearest-neighbor antiferromagetic Ising model was adopted to analyze the temperature dependence of the band structure. The phase transition is due to the one-dimensional-disordered structure (1DDS) at lower temperatures, which turns to a mixture of bi-directional structure domains and disordered molecules at higher temperatures. The number of disordered molecules was deduced to be about 40 percent of the total molecules at 220 K.

关 键 词：K3C60 取向相变机理 单晶薄膜 导带结构 温度 200K 碳化三钾 

分 类 号：O792[理学—晶体学]