Recent positron lifetime measurements for metal oxides had suggested that positron lifetimes in the bulk state of metal oxides were shorter than previously reported. Theoretical calculations of positron lifetimes were performed for bulk and vacancy states in MgO and ZnO by using first-principles electronic structure calculations. By comparing the calculated positron lifetimes with the experimental values, it was found that the semiconductor model reproduced well the experimental positron lifetime. The previously reported longer positron lifetime was considered to arise from not only the bulk but also from the vacancy induced by impurities. In the case of the cation vacancy, the calculated positron lifetime - based upon the semiconductor model - was shorter than the experimental value. This suggested that inward relaxation occurred around the cation vacancy trapping the positron.

Theoretical Calculations of Positron Lifetimes for Metal Oxides. Mizuno, M., Araki, H., Shirai, Y.: Materials Transactions, 2004, 45[7], 1964-7