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Microstructure of ZnO-Li2CO3 compound studied by positron annihilation spectroscopy

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Abstract

Li-doped ZnO polycrystals with Li2CO3 concentration between 0 and 15 at.% have been prepared using a solid state reaction method. After annealing of the mixed samples at 1200 °C, Li2CO3 completely decomposed to Li2O and the lattice parameters a/c first increase with Li2CO3 concentration up to 5 at.%, and then decrease with increasing Li2CO3 concentration. This indicates that Li atoms prefer interstitial sites at low concentration and substitute Zn sites when Li concentration is beyond a certain threshold. Positron annihilation measurements were performed for undoped ZnO and Li2CO3-doped ZnO with 15 at.% samples as a function of annealing temperature. A high concentration of vacancy defects is observed in the undoped and as-prepared Li2CO3-doped samples, and they are fully removed after annealing at 1200 °C. The average positron lifetimes of all Li2CO3-doped samples after annealing at 1200 °C are the same, suggesting that Li doping has little effect on the positron lifetime in ZnO. This might be due to the invisibility of positron to Lii or Lii[BOND]LiZn complex, which is further confirmed by theoretical calculation.

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