Positron and Positronium Annihilation as Probes to Identify Cation Substitution Effects in CoCrxFe2-xO4
CoCrxFe2-xO4 samples with x = 0.0 to 2.0 were prepared by air oxidation of aqueous suspension containing Co2+, Cr3+ and Fe3+ ions and characterized by x-ray diffraction. Positron lifetime and coincidence Doppler broadening (CDB) measurements indicated three distinct stages of positron trapping in defects. Initially the vacancy-type defects located at the A-sites (tetrahedral) trapped positrons but, with the substitution of Fe by Cr in low concentrations (x <= 0.7), positrons are trapped by defects at the B-sites (octahedral). Mossbauer spectroscopic results indicated the cationic distribution at B-sites to be stoichiometry-dependent and, till x = 0.7, the deficiency of Fe3+(B) ions was compensated by interchange of Fe3+(A) ions with Co2+(B) ions. Between x = 0.9 and 1.7, the substitution resulted in continued decrease of Fe3+(B) ions and the structure got fully transformed into a normal spinel configuration during x = 1.8 to 2.0.
Jozef Krištiak, Jan Kuriplach and Pradeep K. Pujari
P.M.G. Nambissan et al., "Positron and Positronium Annihilation as Probes to Identify Cation Substitution Effects in CoCrxFe2-xO4", Materials Science Forum, Vol. 733, pp. 215-218, 2013