K3C60在200K附近的取向相变机理

研究了K₃C₆₀单晶薄膜在200K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220K附近色散不存在.这一实验结果与K₃C₆₀在200K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,K₃C₆₀在200K的相变是由低温下的一维无序取向结构转变为200K以上的双取向结构畴与无序分子(约占40 关键词： 3C₆₀')" href="#">K₃C₆₀ 取向相变机理

MECHANISM FOR THE ORIENTATIONAL PHASE TRANSITION OF K3C60

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.