Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Supplementary Data Info Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (16) Citing Articles via Google Scholar Google Scholar Articles by Keppler, H. Articles by Dubrovinsky, L. S. Search for Related Content GeoRef GeoRef Citation

Optical absorption spectra of ferropericlase to 84 GPa

Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany

Correspondence: ^* E-mail: Hans.Keppler{at}Uni-Bayreuth.de

Optical and near infrared absorption spectra of ferropericlase Mg_0.88Fe_0.12O have been measured to 84 GPa. Under ambient conditions, the spectrum shows two crystal field bands of high-spin Fe²⁺ at 8922 and 12 533 cm^–1, which shift to higher frequencies with increasing pressure (d/dP = 50.7 and 85.5 cm^–1/GPa). Simultaneously, the intensity of the high-frequency band continuously decreases until it vanishes around 40 GPa, suggesting a quenching of the Jahn-Teller effect. Between 51 and 60 GPa, the absorption spectrum changes drastically. Two new bands appear at 60 GPa at 9728 and 14 592 cm^–1 with frequency shifts at higher pressures of d/dP = 23.8 and 21.0 cm^–1/GPa, respectively. If the change in optical spectra between 51 and 60 GPa were interpreted as being due to spin-pairing, the crystal field parameters of low-spin Fe²⁺ at 60 GPa would be = 10 546 cm^–1 and B = 377 cm^–1. This would imply that the main cause of spin-pairing is not the increase in crystal field splitting , but the stronger covalency of the Fe-O bond as seen in the reduction of the Racah parameter B. Even at 84 GPa, ferropericlase is by no means opaque. In particular, the inferred spin-pairing transition between 51 and 60 GPa reduces radiative thermal conductivity only by about 15%. Spin-pairing in ferropericlase is therefore unlikely to have major consequences for the temperature distribution or the mode of convection in the lower mantle. The absorption edge of the high-pressure phase appears to be deeper in the UV than for the low-pressure phase, which could imply a reduced electrical (polaron) conductivity.

Key Words: Ferropericlase • spin-pairing • low-spin • iron • optical spectra • radiative conductivity • crystal field splitting • Racah parameter • Jahn-Teller effect

This article has been cited by other articles:

				H. Marquardt, S. Speziale, H. J. Reichmann, D. J. Frost, F. R. Schilling, and E. J. Garnero Elastic Shear Anisotropy of Ferropericlase in Earth's Lower Mantle Science, April 10, 2009; 324(5924): 224 - 226. [Abstract] [Full Text] [PDF]

				J.-F. Lin, Alexander. G. Gavriliuk, W. Sturhahn, S. D. Jacobsen, J. Zhao, M. Lerche, and M. Hu Synchrotron Mossbauer spectroscopic study of ferropericlase at high pressures and temperatures American Mineralogist, April 1, 2009; 94(4): 594 - 599. [Abstract] [Full Text] [PDF]

				H. Keppler, L. S. Dubrovinsky, O. Narygina, and I. Kantor Optical Absorption and Radiative Thermal Conductivity of Silicate Perovskite to 125 Gigapascals Science, December 5, 2008; 322(5907): 1529 - 1532. [Abstract] [Full Text] [PDF]