INFRARED SPECTROSCOPIC STUDY OF PHASE-TRANSITIONS IN A(1)C(60) COMPOUNDS (A=K,RB,CS)

Optical measurements on doped C-60 films provide evidence for a transi tion from a high temperature conducting phase to a low temperature ins ulating phase in quenched Rb1C60 and K1C60 compounds, while Cs1C60 did not exhibit this behavior. For slow cooled samples our study confirms earlier results indicating phase separation of K1C60 to K3C60 and C-6 0, and the formation of a new Rb1C60 phase at low temperatures. Upon s low cooling Cs1C60 behaves similar to Rb1C60.