Positron annihilation study of the microstructure of Co doped ZnO nanocrystals

ZnO nanopowders are mechanically mixed with a certain quantity of Co 3 O 4 nanopowders to obtain 10at.% Co doped Co 3 O 4 /ZnO composites. The nanocomposites are annealed in argon atmosphere at different temperatures between 100 ℃ and 1200 ℃. The structure and the grain size of the nanocomposite are investigated by X-ray diffraction 2 θ scans. With annealing temperature increasing up to 700 ℃, Co 3 O 4 phase gradually disappears, and ZnO grain size begins to increase significantly. After annealing at above 1000 ℃, Co 3 O 4 phase completely disappears, and CoO phase (rock-salt crystal structure) appears. Positron annihilation lifetime measurements reveal a large number of Zn vacancies and vacancy clusters existing in the interface region of the Co 3 O 4 /ZnO nanocomposites. These defects are gradually recovered after annealing at above 700 ℃, and their number is under the detection limit after annealing at 900 ℃. The same conclusion can be drawn from the coincidence Doppler broadening (CDB) measurements.