Mössbauer-Effect Study of Ca-Substituted Magnetites
Abstract
CaxFe3-xO4 samples, with x≤0.28, prepared from αFe2O3 and CaO by the Bridgeman method were investigated by means of 57 Fe Mössbauer spectroscopy. Room temperature spectra gave evidence that the samples were multi-phase with 73% to 99% contribution of the calciomagnetite, depending on the sample. Analysis of the subspectra associated with the calciomagnetite enabled to conclude that Ca-ions reside on the tetrahedral (A) sites and have not random distribution. They reduce the hyperfine field at Fe nuclei occupying the octahedral positions (B) by 12.3(1.0)kOe per one Ca-ion and cause a decrease of the average hyperfine field, /dx at the rate of 29 kOe/mol% for x≤0.07 and of 387 kOe/mol% for larger x. A linear correlation between and the average isomer shift was revealed to hold. It permitted to conclude that Ca-doping causes a decrease of the spin-density and an increase of the charge-density at Fe nuclei occupying the B-sites of magnetite.