Positron annihilation in hydrogen-doped alkali-metal fullerides

Hydrogen-doped alkali-metal fullerides were studied by means of mass-analyz ed thermal desorption and positron annihilation. The hydrogen desorption sp ectra reveal the inclusion of hydrogen in the fullerides as two types of co mponents; one weakly adsorbed and the other strongly bound, probably as hyd ride ion. The positron lifetime spectra demonstrate that hydrogen-doping to alkali-metal fullerides increases a concentration of higher-order vacancy- type defects, through which more than 50% injected positrons decay with a l ifetime of 0.42-0.71 ns.