Curve fitting complex Mössbauer spectra; application to HoBa2(Cu0.95Fe0.05)3O7.02

Abstract A method for determining the best fit of a complex Mossbauer spectrum is presented and applied to the room temperature 57 Fe Mossbauer spectrum of HoBa 2 (Cu 0.95 Fe 0.05 ) 3 O 7.02 . The method generates many “good fits” as do previous methods. The “best fit”, which is the goal of curve fitting, is selected from the class of good fits by means of a statistical test using the “ F ” function. The best fit for this compound represents 7 doublets. This is significantly larger than the previously reported number (3 or 4) of subspectra associated with REBa 2 (Cu 1− x Fe x ) 3 O y compounds. Assuming no mixed valence, this implies 7 Fe sites. This result is also significantly larger than the previously reported number of Fe sites (1–4) in the REBa 2 (Cu 1− x Fe x ) 3 O y compounds. For 6 of the 7 doublets, the isomer shift, quadrupole splitting and line width are strongly correlated. The valence state corresponding to these 6 doublets is high spin + 4. The seventh doublet is high spin + 3. The sum of Mossbauer site multiplicities is related to the number of accidental degeneracies by a sum rule.