MOSSBAUER-EFFECT STUDY OF CALCIOMAGNETITES

CachiFe3-chiO4 samples, with chi less than or equal to 0.28, prepared from alpha-Fe2O3 and CaO by the Bridgman method were investigated by m eans of Fe-57 Mossbauer spectroscopy. Room temperature spectra gave ev idence that the samples were multiphase, the calciomagnetite being the dominant phase with a contribution of 73% to 99%, depending on the sa mple. Analysis of the subspectra associated with the calciomagnetite g ave evidence that Ca-ions reside on the tetrahedral (A) sites and have not random distribution. Their presence on those sites causes a reduc tion of the hyperfine field at Fe nuclei occupying the octahedral posi tions (B) by 12.3(1.0) kOe per one Ca-ion and a decrease in the averag e hf field, [H-B]/d chi, at the rate of 29 kOe/mol% for chi less than or equal to 0.07 and of 387 kOe/mol% for larger chi. In addition, a li near correlation between [H-B] and the average isomer shift, [I-B], wa s revealed to hold. It indicates that addition of Ca-ions into the mag netite causes a decrease in the spin-density and an increase in the ch arge-density at Fe nuclei occupying the B-sites.