Investigation of cation vacancies in Zinc substituted maghemite by positron annihilation lifetime and Doppler broadening spectroscopy

In this work we investigated vacancies in maghemite and Zn substituted maghemite (γ-Fe2−yZn3y/2O3, y=0.0, 0.11, 0.24, 0.36, 0.50 and 0.66) nanoparticles using coincidence Doppler broadening and positron annihilation lifetime spectroscopy. Coincidence Doppler broadening spectroscopy (CDBS) measurements showed that the positrons annihilated in cation vacancies that surrounded by oxygen anions. Also, the CDBS showed that in pure maghemite and in the y=0.11 samples the vacancies are in octahedral and tetrahedral sites, respectively. For other samples they are distributed in both octahedral and tetrahedral sites. The positron annihilation lifetime spectroscopy (PALS) measurements confirmed the results of the CDBS measurements and also exhibited that the number of vacancies in y=0.36 sample is less than the other samples. This is attributed to Zn substituted magnetite phase in this sample as well as Zn substituted maghemite phase.