Hydrogen bond symmetrization and equation of state of phase D

Journal Article · Tue Oct 09 04:00:00 EDT 2012 · J. Geophys. Res.

DOI:https://doi.org/10.1029/2010JB008087· OSTI ID:1049573

Hushur, Anwar; Manghnani, Murli H; Smyth, Joseph R; Williams, Quentin; Hellebrand, Eric; Lonappan, Dayana; Ye, Yu; Dera, Przemyslaw; Frost, Daniel J ^[1]

---

1. Hawaii

We have synthesized phase D at 24 GPa and at temperatures of 1250-1100 C in a multianvil press under conditions of high silica activity. The compressibility of this high-silica-activity phase D (Mg{sub 1.0}Si{sub 1.7}H{sub 3.0}O{sub 6}) has been measured up to 55.8 GPa at ambient temperature by powder X-ray diffraction. The volume (V) decreases smoothly with increasing pressure up to 40 GPa, consistent with the results reported in earlier studies. However, a kink is observed in the trend of V versus pressure above {approx}40 GPa, reflecting a change in the compression behavior. The data to 30 GPa fit well to a third-order Birch-Murnaghan equation of state (EoS), yielding V{sub o} = 85.1 {+-} 0.2 {angstrom}{sup 3}; K{sub o} = 167.9 {+-} 8.6 GPa; and K{prime}{sub o} = 4.3 {+-} 0.5, similar to results for Fe-Al-free phase D reported by Frost and Fei (1999). However, these parameters are larger than those reported for Fe-Al-bearing phase D and for Fe-Al-free phase D. The abnormal volume change in this study may be attributed to the reported hydrogen bond symmetrization in phase D. Fitting a third-order Birch-Murnaghan EoS to the data below 30 GPa yields a bulk modulus K{sub o} = 173 (2) GPa for the hydrogen-off-centered (HOC) phase and K{sub o} = 212 (15) GPa for the data above 40 GPa for the hydrogen-centered (HC) phase, assuming K{prime}{sub o} is 4. The calculated bulk modulus K{sub o} of the HC phase is 18% larger than the bulk modulus K{sub o} of the HOC phase.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: NSF
• OSTI ID: 1049573
• Journal Information: J. Geophys. Res., Journal Name: J. Geophys. Res. Journal Issue: 2011 Vol. 116; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

08 HYDROGEN
AMBIENT TEMPERATURE
COMPRESSIBILITY
COMPRESSION
HYDROGEN
SILICA
X-RAY DIFFRACTION