Effect of pressure and composition on lattice parameters and unit-cell volume of (Fe,Mg)SiO[subscript 3] post-perovskite

Journal Article · Thu Mar 15 04:00:00 EDT 2012 · Earth Planet. Sci. Lett.

DOI:https://doi.org/10.1016/j.epsl.2011.11.038· OSTI ID:1034178

Zhang, Li; Meng, Yue; Mao, Wendy L ^[1]

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1. Stanford

We obtained unit-cell volumes (V) for (Fe{sub 0.2}Mg{sub 0.8})SiO{sub 3} and (Fe{sub 0.4}Mg{sub 0.6})SiO{sub 3} post-perovskite (PPv) over a pressure (P) range of 80-145 GPa by in-situ X-ray diffraction (XRD) measurements in laser-heated diamond anvil cells (DACs). Our study suggests that the PPv structure is highly resistant to back transformation to Pv and (Fe{sub 0.4}Mg{sub 0.6})SiO{sub 3} PPv was preserved down to 80 GPa upon laser heating during decompression before transforming to pure perovskite (Pv). The bulk modulus (K{sub 0}) of PPv was determined to be 215(1) and 198(1) GPa for (Fe{sub 0.2}Mg{sub 0.8})SiO{sub 3} and (Fe{sub 0.4}Mg{sub 0.6})SiO{sub 3} PPv respectively, with a fixed K'{sub 0} = 4. The substitution of Fe for Mg in PPv results in the largest expansion along the b-axis among all three axes and the expansion of the b-axis is nearly independent of pressure whereas the expansion along the a and c directions slightly decreases with increasing pressure. Combining our results with previous studies on (Fe{sub x},Mg{sub 1-x})SiO{sub 3} PPv (x = 0, 0.09, 0.1) shows that the bulk modulus of PPv decreases with increasing Fe content over a composition range x = 0 to 0.4, varying from 231 GPa for x = 0 to 198 GPa for x = 0.4 with zero pressure volumes scaled to composition, V{sub 0} ({angstrom}{sup 3}) = 162.2 + 19.5x and fixed K'{sub 0} = 4.0. The increase of Fe content in PPv from x = 0 to 0.4 results in a 6.3% increase in density and a 5.3% decrease in bulk sound velocity at 130 GPa.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: NSFDOE - BASIC ENERGY SCIENCES
• OSTI ID: 1034178
• Journal Information: Earth Planet. Sci. Lett., Journal Name: Earth Planet. Sci. Lett. Journal Issue: 02, 2012 Vol. 317-318; ISSN 0012-821X; ISSN EPSLA2
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

58 GEOSCIENCES
DIAMONDS
HEATING
LASERS
LATTICE PARAMETERS
PEROVSKITE
TRANSFORMATIONS
VELOCITY
X-RAY DIFFRACTION