Positron states in fullerites and other carbon phases

The positron states and annihilation characteristics are calculated for different phases of carbon: pure and potassium-doped solid C₆₀, diamond and graphite. In solid C₆₀ with the FCC structure the positron is concentrated in the interstitial space between the C₆₀ molecules. For the different carbon phases the calculated positron lifetimes reproduce well the experimental results in a wide range from about 100 ps for diamond to 400 ps for fullerite. The effects of interstitial dopants on the positron distribution and lifetime are studied for the solid C₆₀. Finally, the positron characteristics for the compound K_xC ₆₀ are predicted and found to be sensitive to the potassium concentration.