Phase instabilities in KC_60

摘要

The high-temperature f.c.c. phase of KC_60 is unstable upon cooling and transforms into the orthorhombic polymer (OP). We show in this paper that the polymeric phase is also unstable above room temperature and separates into the thermodynamically stable K_3C_60+alpha-C_60 phases. The analysis of the lifetime of both f.c.c. and polymeric phases, probed by ESR as a function of temperature, allows the determination of activation energies of both f.c.c. -> polymeric and polymeric -> K_3C_60 + alpha-C_60 phase transformations, as being 0.17 and 1.1 eV, respectively.