LOCAL-STRUCTURE OF AS-PREPARED AND PARTIALLY REDUCED CO,TI,SN-SUBSTITUTED BA-HEXAFERRITE POWDER

In this study, the local structure around Fe and Co atoms in as-prepar ed and partially reduced Co,Ti,Sn-substituted Ba-hexaferrite powders a re examined using extended x-ray absorption fine structure (EXAFS). It appears that the substitutional atoms in general and Co in particular show a preference for the Fe(IV) and Fe(III) sites. After partial red uction in H-2 at 300 degrees C, both the Fe and Co EXAFS show a mixtur e of two phases: substituted Ba-hexaferrite and bce metal. There does not appear to be any large preference in reduction among the five diff erent types of Fe sites. However, a much larger fraction of the Co is reduced than is the Fe. Thus the partially reduced sample is not merel y a collection of unreduced and totally reduced particles. The after-r eduction spectra for both Fe and Co EXAFS were fit using a linear comb ination of spectra from as-prepared material and bcc metal, which enab led quantitative calculation of the relative fraction of each metal re duced. (C) 1997 American Institute of Physics.