Mössbauer-derived equilibrium iron isotope fractionation factors for troilite (FeS) and aegirine (NaFeSi2O6)
摘要
Troilite was synthesized and its Mössbauer spectra in the temperature range 90 ÷ 295 K were obtained. The equilibrium iron isotope fractionation factors (β-factors) for troilite were estimated from the temperature shift (TS) in the Mössbauer spectra. The TS was described by the Debye model, and the Mössbauer temperature (θM) was calculated. It is shown that the quantum component of TS, at temperatures above ~ 0.6θM, does not exceed the statistical error of the measurements. The use of experimental results at these temperatures leads to significant errors in the estimation of θM. Based on Mössbauer data at temperatures below 0.6θM (from 90 to 190 K), θM = 319 K was found. The temperature dependence of the iron β-factor for troilite, calculated from this value of θM, is as follows: 57Fe/54Fe 103lnβ = 0.42388x − 0.51351 × 10−3x2 + 0.96769 × 10−6x3; x = 106/T2 where T is the absolute temperature. The Mössbauer temperature dependence of the iron β-factor for troilite agrees well with the results of its estimation by nuclear resonance inelastic X-ray scattering on 57Fe nuclei. The same approach was applied to assess the iron β-factors for aegirine. Previously obtained θM = 540 K for aegirine was corrected down to θM = 479 K using Mössbauer data at temperatures below 0.6θM. The temperature dependence of the iron β-factor for aegirine: 57Fe/54Fe 103lnβ = 0.95573x − 2.6105 × 10−3x2 11.09185 × 10−6x3 matches with that from the first principal calculations. This resolves the contradiction between Mössbauer-derived and first principle calculated iron β-factors for aegirine.