Ni-Substitution Induced Inversion in ZnFe2O4 Seen by Positron Annihilation
We report in this work about the inversion of the spinel structure of ZnFe2O4 induced by the substitution of Zn2+ by Ni2+ ions. Positron lifetimes were measured in Zn1-xNixFe2O4 with different concentrations (x) of doped Ni2+ ions and a drastic change across x = 0.4 – 0.6 was observed, which is attributed to this transformation. The interchange of positions of the cations on doping leaves a fraction of them unoccupied and these vacancies act as positron trapping centres. Since Ni2+ is smaller in size than Zn2+, defects due to non-stoichiometry are less in NiFe2O4 than in ZnFe2O4. The increase in positron lifetime implies the trapping of positrons being shifted from A- to B-sites and is an indication of the transformation from inverse to normal spinel configuration. Coincidence Doppler broadening measurements supported these findings.
Jozef Krištiak, Jan Kuriplach and Pradeep K. Pujari
P.M.G. Nambissan et al., "Ni-Substitution Induced Inversion in ZnFe2O4 Seen by Positron Annihilation", Materials Science Forum, Vol. 733, pp. 219-223, 2013