J. Phys. IV France 07 (1997) C1-589-C1-590
Mössbauer-Effect Study of Ca-Substituted MagnetitesJ. Cieslak1, S.M. Dubiel1, J. Orewczyk2 and S. Jasienska2
1 Faculty of Physics and Nuclear Techniques
2 Faculty of Metallurgy and Material Engineering, The University of Mining and Metallurgy (AGH), al. Mickiewicza 30, 30-059 Krakow, Poland
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, <Hb>/dx at the rate of 29 kOe/mol% for x≤0.07 and of 387 kOe/mol% for larger x. A linear correlation between <Hb> and the average isomer shift <Ib> 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.
© EDP Sciences 1997