Quantitative determination of the oxidation state of iron in biotite using X-ray photoelectron spectroscopy: I. Calibration

• Published in: Geochimica et cosmochimica acta Vol. 61; no. 21; pp. 4519 - 4530
• Main Authors: Raeburn, Stuart P., Ilton, Eugene S., Veblen, David R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.1997
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/S0016-7037(97)00263-9

X-ray photoelectron spectroscopy (XPS) analyses of Fe(III)/ΣFe were calibrated with nine single crystals of biotite of known Fe(III)/ΣFe content. Peak shape parameters for the component Fe 2+ and Fe 3+ Fe 3p peaks were obtained by a constrained least squares fitting method that minimized the difference between Fe(IIl)/EFe determined by XPS and wet chemistry /electron microprobe (WCEM) analyses. Fe 2+ and Fe 3+ peak separation was estimated from the separation of minima in the second derivative of Fe 3p spectra. The single set of derived peak parameters yielded a good linear correlation ( r = 0.87) between XPS and WCEM values over the sample range of 2–20% Fe(RI)/ΣFe. Target transformation factor analysis of a time series of spectra for a sample displaying progressive oxidation during XPS analysis resulted in Fe 2+ and Fe 3+ component peak shapes largely consistent with the constrained least squares fitting method. Peak asymmetry for the Fe 3+ component was the only parameter that differed for the two methods. Beam damage, which appeared to be restricted to three single crystals with low ΣFe, low Fe/Mg, and high Fe(II)/ΣFe, caused increases in Fe(III)/ΣFe that were proportional to the duration of sample exposure.