Positron states in C60 and potassium-doped C60 crystals

Abstract

Positron lifetimes and distributions in C60 and potassium-doped C60 crystals are calculated using the superposed-atom model and the numerical relaxation technique. In the calculation on pure C60, the high-frequency dielectric constant is treated as a parameter and has been determined to be approximately 3.5 by fitting the lifetime to the experimental value. Positrons are distributed predominantly at the octahedral interstices in pure C60. The lifetime and the distribution of positrons are significantly affected by potassium doping when the dopant atoms occupy the octahedral sites, whereas they are not altered much by doping at the tetrahedral sites or at the centre of the C60 cluster. It is revealed that the positron is a very sensitive probe of dopant atoms occupying the octahedral sites. Possible applications are discussed.