Defect dependence of positron lifetimes in oxide superconductors

First principles calculations of the positron lifetimes are used to interpret experimental lifetime data for Ba(sub 1-x)K(sub x)BiO(sub 3). The observed lifetimes are found to be very sensitive to the presence of defects in the sample. The temperature dependence of the lifetime and the change in lifetime with sample aging are both attributed to defects. The qualitative differences between metal vacancy defects and oxygen vacancy defects in metal oxides are also discussed.