Phase stability of iron germanate, FeGeO3, to 127 GPa
The high-pressure behavior of germanates is of interest as these compounds serve as analogs for silicates of the deep Earth. Current theoretical and experimental studies of iron germanate, FeGeO3, are limited. Here, we have examined the behavior of FeGeO3 to 127 GPa using the laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction. Upon compression at room temperature, the ambient-pressure clinopyroxene phase transforms to a disordered triclinic phase [FeGeO3 (II)] at ~ 18 GPa in agreement with earlier studies. An additional phase transition to FeGeO3 (III) occurs above 54 GPa at room temperature. Laser-heating experiments (~ 1200–2200 K) were conducted at three pressures (33, 54, and 123 GPa) chosen to cover the stability regions of different GeO2 polymorphs. In all cases, we observe that FeGeO3 dissociates into GeO2 + FeO at high pressure and temperature conditions. Neither the perovskite nor the post-perovskite phase was observed up to 127 GPa at ambient or high temperatures. The results are consistent with the behavior of FeSiO3, which also dissociates into a mixture of the oxides (FeO + SiO2) at least up to 149 GPa.
KeywordsGermanates Phase-transitions Diamond anvil cell High-pressure
The authors are grateful to Drs. J. Wicks, S. Tkachev, C. Prescher, and J. Krizan for experimental assistance. This work was supported by the National Science Foundation (EAR-1415321). The authors’ acknowledge use of the Advanced Photon Source, an Office of Science User Facility, U.S. Department of Energy. GeoSoilEnviroCARS (GSECARS, Sector 13), is supported by the NSF Earth Sciences (Grant No: EAR-1128799) and the Department of Energy, Geosciences (Grant No. DE-FG02-94ER14466). C. Stan acknowledges support from DOE Office of Science User Facility contract No. DE-AC02-05CH11231. The use of the gas-loading facility at GSECARS was partially supported by the Consortium for Materials Properties Research in Earth Sciences.
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