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Title: Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O

Abstract

Ringwoodite ({gamma}-Mg{sub 2}SiO{sub 4}) is the stable polymorph of olivine in the transition zone between 525-660 km depth, and can incorporate weight percent amounts of H{sub 2}O as hydroxyl, with charge compensated mainly by Mg vacancies (Mg{sup 2+} = 2H{sup +}), but also possibly as (Si{sup 4+} = 4H{sup +} and Mg{sup 2+} + 2H{sup +} = Si{sup 4+}). We synthesized pure Mg ringwoodite containing 2.5(3) wt% H{sub 2}O, measured by secondary ion mass spectrometry (SIMS), and determined its compressibility at 300 K by single-crystal and powder X-ray diffraction (XRD), as well as its thermal expansion behavior between 140 and 740 K at room pressure. A third-order Birch-Murnaghan equation of state (BM3 EOS) fits values of the isothermal bulk modulus K{sub T0} = 159(7) GPa and (dK{sub T}/dP){sub P = 0} = K' = 6.7(7) for single-crystal XRD; K{sub T0} = 161(4) GPa and K' = 5.4(6) for powder XRD, with K{sub T0} = 160(2) GPa and K' = 6.2(3) for the combined data sets. At room pressure, hydrous ringwoodite breaks down by an irreversible unit-cell expansion above 586 K, which may be related to dehydration and changes in the disorder mechanisms. Single-crystal intensity data were collected at various temperaturesmore » up to 736 K, and show that the cell volume V(cell) has a mean thermal expansion coefficient {alpha}{sub V0} of 40(4) x 10{sup -6}/K (143-736 K), and 29(2) x 10{sup -6}/K (143-586 K before irreversible expansion). V(Mg) have {alpha}{sub 0} values of 41(3) x 10{sup -6}/K (143-736 K), and V(Si) has {alpha}{sub 0} values of 20(3) x 10{sup -6}/K (143-586 K) and 132(4) x 10{sup -6}K (586-736 K). Based on the experimental data and previous work from {sup 29}Si NMR, we propose that during the irreversible expansion, a small amount of H{sup +} cations in Mg sites transfer to Si sites without changing the cubic spinel structure of ringwoodite, and the substituted Si{sup 4+} cations move to the normally vacant octahedral site at (1/2, 1/2, 0). Including new SIMS data on this and several Mg-ringwoodite samples from previous studies, we summarize volume-hydration data and show that the Mg{sup 2+} = 2H{sup +} dominates up to about 2 wt% H{sub 2}O, where a discontinuity in the volume vs. H{sub 2}O content trend suggests that other hydration mechanisms become important at very high H{sub 2}O contents.« less

Authors:
; ; ; ; ; ; ; ; ; ;  [1];  [2];  [2];  [2];  [2];  [2]
  1. (Bayreuth)
  2. (
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
DOE - BASIC ENERGY SCIENCESDOE - OTHERNSFOTHER
OSTI Identifier:
1037479
Resource Type:
Journal Article
Resource Relation:
Journal Name: American Mineralogist; Journal Volume: 97; Journal Issue: (4) ; 04, 2012
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

Ye, Yu, Brown, David A., Smyth, Joseph R., Panero, Wendy R., Jacobsen, Steven D., Chang, Yun-Yuan, Townsend, Joshua P., Thomas, Sylvia-Monique, Hauri, Erik H., Dera, Przemyslaw, Frost, Daniel J., Colorado), CIW), UC), NWU), and OSU). Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O. United States: N. p., 2016. Web. doi:10.2138/am.2012.4010.
Ye, Yu, Brown, David A., Smyth, Joseph R., Panero, Wendy R., Jacobsen, Steven D., Chang, Yun-Yuan, Townsend, Joshua P., Thomas, Sylvia-Monique, Hauri, Erik H., Dera, Przemyslaw, Frost, Daniel J., Colorado), CIW), UC), NWU), & OSU). Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O. United States. doi:10.2138/am.2012.4010.
Ye, Yu, Brown, David A., Smyth, Joseph R., Panero, Wendy R., Jacobsen, Steven D., Chang, Yun-Yuan, Townsend, Joshua P., Thomas, Sylvia-Monique, Hauri, Erik H., Dera, Przemyslaw, Frost, Daniel J., Colorado), CIW), UC), NWU), and OSU). Fri . "Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O". United States. doi:10.2138/am.2012.4010.
@article{osti_1037479,
title = {Compressibility and thermal expansion of hydrous ringwoodite with 2.5(3) wt% H[subscript 2]O},
author = {Ye, Yu and Brown, David A. and Smyth, Joseph R. and Panero, Wendy R. and Jacobsen, Steven D. and Chang, Yun-Yuan and Townsend, Joshua P. and Thomas, Sylvia-Monique and Hauri, Erik H. and Dera, Przemyslaw and Frost, Daniel J. and Colorado) and CIW) and UC) and NWU) and OSU)},
abstractNote = {Ringwoodite ({gamma}-Mg{sub 2}SiO{sub 4}) is the stable polymorph of olivine in the transition zone between 525-660 km depth, and can incorporate weight percent amounts of H{sub 2}O as hydroxyl, with charge compensated mainly by Mg vacancies (Mg{sup 2+} = 2H{sup +}), but also possibly as (Si{sup 4+} = 4H{sup +} and Mg{sup 2+} + 2H{sup +} = Si{sup 4+}). We synthesized pure Mg ringwoodite containing 2.5(3) wt% H{sub 2}O, measured by secondary ion mass spectrometry (SIMS), and determined its compressibility at 300 K by single-crystal and powder X-ray diffraction (XRD), as well as its thermal expansion behavior between 140 and 740 K at room pressure. A third-order Birch-Murnaghan equation of state (BM3 EOS) fits values of the isothermal bulk modulus K{sub T0} = 159(7) GPa and (dK{sub T}/dP){sub P = 0} = K' = 6.7(7) for single-crystal XRD; K{sub T0} = 161(4) GPa and K' = 5.4(6) for powder XRD, with K{sub T0} = 160(2) GPa and K' = 6.2(3) for the combined data sets. At room pressure, hydrous ringwoodite breaks down by an irreversible unit-cell expansion above 586 K, which may be related to dehydration and changes in the disorder mechanisms. Single-crystal intensity data were collected at various temperatures up to 736 K, and show that the cell volume V(cell) has a mean thermal expansion coefficient {alpha}{sub V0} of 40(4) x 10{sup -6}/K (143-736 K), and 29(2) x 10{sup -6}/K (143-586 K before irreversible expansion). V(Mg) have {alpha}{sub 0} values of 41(3) x 10{sup -6}/K (143-736 K), and V(Si) has {alpha}{sub 0} values of 20(3) x 10{sup -6}/K (143-586 K) and 132(4) x 10{sup -6}K (586-736 K). Based on the experimental data and previous work from {sup 29}Si NMR, we propose that during the irreversible expansion, a small amount of H{sup +} cations in Mg sites transfer to Si sites without changing the cubic spinel structure of ringwoodite, and the substituted Si{sup 4+} cations move to the normally vacant octahedral site at (1/2, 1/2, 0). Including new SIMS data on this and several Mg-ringwoodite samples from previous studies, we summarize volume-hydration data and show that the Mg{sup 2+} = 2H{sup +} dominates up to about 2 wt% H{sub 2}O, where a discontinuity in the volume vs. H{sub 2}O content trend suggests that other hydration mechanisms become important at very high H{sub 2}O contents.},
doi = {10.2138/am.2012.4010},
journal = {American Mineralogist},
number = (4) ; 04, 2012,
volume = 97,
place = {United States},
year = {Fri Jul 29 00:00:00 EDT 2016},
month = {Fri Jul 29 00:00:00 EDT 2016}
}