reprint - joseph smyth - university of colorado boulder

ORIGINAL PAPER

Crystal structure, Raman and FTIR spectroscopy, and equationsof state of OH-bearing MgSiO3 akimotoite

Yu Ye • Joseph R. Smyth • Steven D. Jacobsen • Wendy R. Panero • David A. Brown •

Tomoo Katsura • Yun-Yuan Chang • Joshua P. Townsend • Przemyslaw Dera •

Sergey Tkachev • Cayman Unterborn • Zhenxian Liu • Celine Goujon

Received: 18 December 2012 / Accepted: 23 July 2013 / Published online: 14 August 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract MgSiO3 akimotoite is stable relative to majorite-

garnet under low-temperature geotherms within steeply or

rapidly subducting slabs. Two compositions of Mg–akimot-

oite were synthesized under similar conditions: Z674 (con-

taining about 550 ppm wt H2O) was synthesized at 22 GPa

and 1,500 �C and SH1101 (nominally anhydrous) was syn-

thesized at 22 GPa and 1,250 �C. Crystal structures of both

samples differ significantly from previous studies to give

slightly smaller Si sites and larger Mg sites. The bulk thermal

expansion coefficients of Z674 are (153–839 K) of

a1 = 20(3) 9 10-9 K-2 and a0 = 17(2) 9 10-6 K-1, with

an average of a0 = 27.1(6) 9 10-6 K-1. Compressibility at

ambient temperature of Z674 was measured up to 34.6 GPa at

Sector 13 (GSECARS) at Advanced Photon Source Argonne

National Laboratory. The second-order Birch–Murnaghan

equation of state (BM2 EoS) fitting yields:

V0 = 263.7(2) A3, KT0 = 217(3) GPa (K0 fixed at 4). The

anisotropies of axial thermal expansivities and compress-

ibilities are similar: aa = 8.2(3) and ac = 10.68(9)

(10-6 K-1); ba = 11.4(3) and bc = 15.9(3) (10-4 GPa).

Hydration increases both the bulk thermal expansivity and

compressibility, but decreases the anisotropy of structural

expansion and compression. Complementary Raman and

Fourier transform infrared (FTIR) spectroscopy shows mul-

tiple structural hydration sites. Low-temperature and high-

pressure FTIR spectroscopy (15–300 K and 0–28 GPa)

confirms that the multiple sites are structurally unique, with

zero-pressure intrinsic anharmonic mode parameters

between -1.02 9 10-5 and ?1.7 9 10-5 K-1, indicating

both weak hydrogen bonds (O–H��O) and strong OH bonding

due to long O��O distances.

Communicated by T. L. Grove.

Y. Ye (&)

Department of Physics, University of Colorado,

Boulder, CO 80309, USA

e-mail: [email protected]

Present Address:

Y. Ye

School of Earth and Space Exploration, Arizona State

University, Tempe, AZ 85287, USA

J. R. Smyth � D. A. Brown

Department of Geological Sciences, University of Colorado,

Boulder, CO 80309, USA

S. D. Jacobsen � Y.-Y. Chang � J. P. Townsend

Department of Earth and Planetary Sciences, Northwestern

University, Evanston, IL 60208, USA

W. R. Panero � C. Unterborn

School of Earth Sciences, Ohio State University,

Columbus, OH 43210, USA

T. Katsura

Bayerisches Geoinstitut, Universitat Bayreuth,

95440 Bayreuth, Germany

P. Dera � S. Tkachev

Center for Advanced Radiation Sources,

University of Chicago, Argonne National Laboratory,

Argonne, IL 60439, USA

Z. Liu

Geophysical Laboratory, Carnegie Institution of Washington,

Washington, DC 20015, USA

C. Goujon

Institut Neel, CNRS and Universite Joseph Fourier,

BP 166, 38042 Grenoble Cedex 9, France

123

Contrib Mineral Petrol (2013) 166:1375–1388

DOI 10.1007/s00410-013-0933-y

Keywords Akimotoite � Crystal structure � Thermal

expansion � Compressibility � Anisotropy � FTIR

Introduction

Akimotoite (ilmenite-type MgSiO3) is stable at pressures of

18–25 GPa and up to about 2,000 K in the MgSiO3 system,

with wadsleyite plus stishovite stable at lower pressures,

majorite stable at higher temperatures, and silicate perov-

skite stable at higher pressures and temperatures (e.g., Ito

and Matsui 1977; Sawamoto 1987; Kato et al. 1995; Kuroda

et al. 2000; Gasparik 1990). Wang et al. (2004) measured

the P–V–T equation of state of akimotoite and examined the

possible influence of akimotoite–majorite phase transitions

on the seismic structure of the 660-km seismic discontinu-

ity, where akimotoite could be stable along cold subduction

geotherms. The crystal structure of akimotoite (trigonal

system, space group R�3, Z = 6) was determined by Ito and

Matsui (1977) and refined by Horiuchi et al. (1982) with

unit-cell parameters a = 4.7284 A, c = 13.5591 A, and

corresponding density, q0 = 3.810 g/cm3.

Ashida et al. (1988) measured the thermal expansivity of

akimotoite between 300 and 900 K from polycrystalline

X-ray diffraction data, fitting linear coefficients of thermal

expansivity to the lattice parameters, resulting in a volume

expansion coefficient, a0 = 2.44 9 10-5 K-1. Reynard

et al. (1996) studied the compressibility of akimotoite from

powder X-ray diffraction in a diamond anvil cell up to

28 GPa, using H2O as a pressure medium. In that study,

Reynard et al. (1996) fixed KT0 = 212 GPa from previous

Brillouin scattering results (Weidner and Ito 1985) to refine

dK/dP = K0 = 7.5(±1.0) using ruby fluorescence pres-

sures and K0 = 5.6 using pressures determined from the

equation of state of the H2O pressure medium. Wang et al.

(2004) measured the P–V–T equation of state of akimotoite

up to 19 GPa and 1,373 K and refined a volume coefficient

of thermal expansivity, a0 = 2.41(19) 9 10-5 K-1 with

K0 = 5.6 when KT0 was fixed to 210 GPa. First-principals

lattice dynamics calculations found comparable results

with KT0 = 201 GPa, K0 = 4.64, and a0 = 1.88 9

10-5 K-1 at 300 K (Karki and Wentzcovitch 2002), and an

ab initio study of the elastic behavior gives an adiabatic

bulk modulus (KS) of 222 GPa, with K0 = 4.5 (Da Silva

et al. 1999).

Bolfan-Casanova et al. (2002) studied the incorporation

of H2O into akimotoite, finding up to *350 ppm wt H2O

(calibration of Patterson 1982) in samples synthesized at

19–21 GPa and 1,573–1,773 K. Because of its potential

role in transporting H2O into the lower mantle along cold

subduction geotherms, we have undertaken this study to

determine the influence of H2O on the crystal structure,

thermal expansivity, compressibility, and vibrational

properties of OH-akimotoite for comparison with anhy-

drous akimotoite. In this study, we report crystal structure

refinements of two akimotoite samples, one containing

\*50 ppm wt H2O (sample SH1101) and a hydrous

sample (Z674) containing *550 ppm wt H2O. The com-

pressibility of the hydrous sample (Z674) was determined

by single-crystal synchrotron X-ray diffraction up to

35 GPa Thermal expansivity of the hydrous akimotoite

sample (Z674) was determined by single-crystal X-ray

diffraction on a laboratory rotating anode source between

153 and 839 K. The anisotropy of thermal expansivity and

compressibility is discussed. In addition, low-temperature

(10–300 K) synchrotron FTIR spectra for OH-akimotoite

were measured up to 28 GPa to determine the isobaric and

isothermal mode Gruneisen parameters, as well as an

intrinsic anharmonic mode parameter. Finally, we sum-

marize relationships between isothermal bulk moduli and

density for anhydrous and hydrous MgSiO3 and Mg2SiO4

polymorphs.

Experimental methods and results

Sample synthesis

Hydrous akimotoite sample Z674 was synthesized using

the 5,000 ton press at Bayerisches Geoinstitut, Universitat

Bayreuth, Germany. The welded Pt capsule was 2.4 mm

diameter by 6.7 mm in length. The capsule was placed into

a 14-mm sintered MgO octahedron with a stepped LaCrO3

ceramic heater. The anvils were 54-mm WC cubes with

6-mm corner truncations. The starting material was

85 wt% enstatite and 15 wt% forsterite with an additional

15 wt% H2O as liquid water and synthesized at 22 GPa and

1,500 �C for 8 h.

Nominally anhydrous akimotoite sample SH1101 was

synthesized using the 1,500 ton press at Bayerisches

Geoinstitut, Universitat Bayreuth, Germany. The welded Pt

capsule was 1.2 mm diameter by 2.4 mm in length. The

capsule was in a 10-mm sintered MgO octahedron with a

stepped LaCrO3 ceramic heater. The anvils were 28-mm

WC cubes with 4-mm corner truncations. The starting

material was mixed from powders of MgO (periclase),

SiO2 (quartz), and Mg(OH)2 (brucite) to give stoichiome-

tric MgSiO3 with an additional 2 H2O wt% as OH in

brucite and synthesized at 22 GPa and 1,250 �C for 4 h.

Raman and infrared spectroscopy

Raman and Fourier transform infrared (FTIR) spectroscopy

at ambient conditions was used for sample characterization.

Raman spectra of crystals from runs Z674 and SH1101

were obtained using a 250-mW, 458-nm solid-state diode

1376 Contrib Mineral Petrol (2013) 166:1375–1388

123

laser source (Melles Griot 85-BLS-601). A confocal optical

system with an Olympus-BX microscope and 1009

objective was used to collect spectra for 60 s and averaged

over 3 accumulations, with about 10-mW laser power at the

sample. Spectra were collected using an Andor Shamrock

303i spectrograph (0.3 m focal length) with a grating of

1,200 lines per mm and Newton DU-970 electron-multi-

plying CCD camera. Spectra were obtained from 0 to

4,000 cm-1 shift from the laser line at 1.3 cm-1 resolution.

This setup is particularly useful for studies of Raman shifts

in the OH region because excitation with 458 nm positions

Raman shifts from O–H (3,000–3,600 cm-1 shift) at

530–550 nm, where the CCD camera has highest quantum

efficiency. Unpolarized Raman spectra of akimotoite sam-

ples Z674 and SH1101 in the lattice mode region

(0–1,000 cm-1) are shown in Fig. 1. Raman spectra in the

OH region are plotted in Fig. 2, showing three distinct O–H

stretching modes in akimotoite Z674, whereas akimotoite

SH1101 is nominally anhydrous.

FTIR spectra of akimotoite Z674 were collected from

800 to 4,000 cm-1 at 2 cm-1 resolution and 512 scans

using a Bruker Tensor-37 spectrometer equipped with a

Hyperion microscope, 159 objective, a 250-lm pixel size

MCT detector, KBr beam splitter, and a globar light

source. Two different akimotoite crystals of unknown ori-

entation from run Z674 (called crystal-1 and crystal-2 in

Fig. 3) were measured with unpolarized light. Both sam-

ples were about 150–200 lm in size and polished to about

60 lm thickness.

High-pressure, low-temperature FTIR data for sample

Z674 were measured at the U2A synchrotron-IR beamline

of the National Synchrotron Light Source (NSLS). Data

Fig. 1 Unpolarized Raman spectra of akimotoite crystals from runs

Z674 and SH1101 in the lattice mode regionFig. 2 Unpolarized Raman spectra of akimotoite crystals from runs

Z674 and SH1101 in the O–H stretching region. In Z674, three

distinct O–H stretching modes are observed at 3,295, 3,320, and

3,350 cm-1, whereas SH1101 is nominally anhydrous

Fig. 3 Unpolarized FTIR spectra of two crystals from run Z674

Contrib Mineral Petrol (2013) 166:1375–1388 1377

123

Fig. 4 High-pressure, low-temperature FTIR spectra of Z674 in the order of increasing pressure: a zero-pressure, b 5–10 GPa, c 10–14 GPa, and

d 21–26 GPa


123

were collected on the custom long-working distance

microscope with a beam aperture of *30 lm, using a KBr

beam splitter and an MCT detector. All spectra were col-

lected with 512 or 1,024 scans with 4 cm-1 spectral

resolution.

A doubly polished fragment of Z674 was loaded with a

ruby chip in an Ar pressure medium in a symmetric dia-

mond cell with type IIa diamond anvils and compressed to

21 GPa. Cooling of the DAC was done in a CRYO

Industries cryostat model 102-2572-DCA, cooled with

liquid helium using Varian TPS-compact vacuum system

to *10-4 Pa. Temperature stability and accuracy of the

temperature controller is \0.1 K at T [50 K; *0.5 K for

T \20 K. Upon cooling, the pressure in the cell increases

due to thermal contraction. A small ruby sphere was

therefore mounted on the back of one of the diamonds both

to serve as an internal measure of the zero-pressure R1 shift

and to confirm that the cryostat thermocouple temperature

located above the diamond cell accurately reflects the

temperature of the sample itself. High-pressure data were

collected during three cooling cycles at 21–28, 11–16, and

5.5–10 GPa via cooling at *10 K and then collecting

spectra upon warming up to room temperature. The spectra

at pressures and temperatures are shown in Fig. 4a–d,

and the peak positions versus T and P are listed in

‘‘Appendix 1’’.

Structure refinements

Single crystals from runs Z674 and SH1101 were selected for

structure refinement at ambient conditions, measuring

120 9 105 9 85 lm3 for Z674 and 105 9 90 9 80 lm3 for

SH1101. Unit-cell parameters of each crystal were refined on a

Bruker P4 four-circle diffractometer with a dual-scintillation

point detector system, which used 18-kW rotating Mo-anode

X-ray generator operating at 50 kV and 250 mA. MoKa1-Ka2

mixed characteristic wavelength was used with Ka_avg =

0.71080 A, which was calibrated by a single crystal of anhy-

drous forsterite of spherical shape. Least squares fitting was

performed on 42 centered reflections within the following

classes: (104), (015), (213), (113), (021), (024), (107), (205),

(216), (116), (018), (312) and (314). The unit-cell parameters

are as follows: a = 4.7283(6) A, c = 13.560(2) A, V =

262.55(6) A3 for Z674; a = 4.7295(3) A, c = 13.5601(13) A,

V = 262.68(4) A3 for SH1101. For comparison, Ito and Mat-

sui (1977) studied a sample of akimotoite with a =

4.7284(4) A, c = 13.5591(16) A, V = 262.54(4) A3. Inten-

sity data for both single crystals were collected using a Bruker

APEX II CCD detector mounted on a P4 diffractometer up to

70� 2h. Refinement of atom positions and anisotropic dis-

placement parameters were carried out using SHELXL-97

(Sheldrick 1997) in the software package WinGX (Farrugia

1999). We used scattering factors of Mg2? and Si4? reported by

Cromer and Mann (1968), and those of O2- from Tokonami

(1965). The intensity data collection parameters and refined

atomic position coordinates as well as the unit-cell parameters

are listed in Table 1, and the anisotropic displacement

parameters are listed in Table 2.

The same single crystal of Z674 used for structure

refinement was used for thermal expansion studies between

150 and 900 K at ambient pressure. At each temperature

step, the unit-cell parameters were refined following the

same procedure at ambient temperature described above.

Three low-temperature measurements were conducted at

253, 203, and 153 K. Low temperatures were measured

and controlled by a Bruker LT-2A controller, which uses a

low-temperature N2 gas stream. Next, the single crystal

was transferred inside a silica glass capillary for high-

temperature experiments. Eleven high-temperature points

were taken up to 839 K using a Bruker high-temperature

device, which uses a two-prong ceramic-coated Pt wire

radiant heater, with an Omega temperature control unit. Ye

et al. (2009) reported the temperature calibration in detail.

Unit-cell parameters at various temperatures are listed in

‘‘Appendix 2’’.

High-pressure synchrotron X-ray diffraction

High-pressure XRD experiments for sample Z674 were

conducted at beamline 13-BM-D (GSECARS) of the

Advanced Photon Source (APS) at Argonne National

Laboratory. The single crystal used for the high-pressure

experiment measured about 35 9 30 9 20 lm. We used a

symmetric piston-cylinder-type diamond anvil cell (DAC)

with 300 lm culets. The diamond cell was fitted with a

cubic boron nitride (cBN) seat on the downstream side and

a tungsten carbide (WC) seat on the upstream side. We

used a rhenium gasket, pre-indented to an initial thickness

of *40 lm with a 160-lm-diameter hole. The DAC was

loaded with neon as pressure medium using the COM-

PRES/GSECARS gas-loading system (Rivers et al. 2008).

The pressure inside the cell was about 1.4 GPa after gas

loading, and the gasket-hole diameter decreased by about

30 %. Fine gold powder was mounted in the sample

chamber along with sample to serve as the pressure scale

(Dorogokupets and Dewaele 2007).

Throughout the experiment, monochromatic synchro-

tron radiation with wavelength k = 0.33442 A was used to

collect diffraction patterns on a MAR345 image plate. The

single-crystal diffraction data collection at each pressure

took 10–12 min with omega rotation from ±25�. To obtain

the orientation matrix at the initial pressure of 1.38 GPa, an

omega step-scan was performed with 1� steps. In total, 50

images were collected to calculate omega angles for each

reflection and the orientation matrix, as well as to refine


123

unit-cell parameters. This orientation matrix was used as a

first approximation to index peaks in images collected at

subsequent pressures. For each pressure step, about 30–40

reflection peaks were used to refine the unit-cell parameters

by the software packages of GSE-ADA (Dera 2007a) and

RSV (Dera 2007b). The unit-cell parameters at various

pressures are listed in ‘‘Appendix 3’’.

Discussion

H2O content calibration

From our FTIR and Raman spectra alone, it is not possible

to accurately quantify the H2O content of the akimotoite

samples. Figure 3 shows unpolarized FTIR spectra of two

crystals from run Z674. In agreement with spectra of OH-

bearing akimotoite from Bolfan-Casanova et al. (2002), we

observe three strong bands at 3,300, 3,320, and

3,390 cm-1, and one weak band around 3,260 cm-1. In

addition, we observe three previously unreported OH bands

at 3,250, 3,345, and 3,410 cm-1. Using the general cali-

bration of Libowitzky and Rossman (1997) on the peaks

shown in Fig. 3, we obtain integrated molar absorption

coefficients (eI) of 1.006 9 105 and 0.989 9 105 cm-2 per

mol H2O/L, respectively, corresponding to H2O contents of

440 ppm wt H2O for crystal-1 and 700 ppm wt H2O for

crystal-2, using the calibration from Libowitzky and

Rossman (1997). For the purpose of comparison with

Bolfan-Casanova et al. (2002), we also applied the Patt-

erson (1982) calibration to the spectra in Fig. 3 and

obtained 250 and 400 ppm wt H2O for crystal-1 and

crystal-2, respectively. In this paper, we take the average of

the two crystals using the Libowitzky and Rossman (1997)

calibration and consider the H2O content of Z674 to be

*550 ppm wt H2O, with an estimated uncertainty of about

200 ppm wt H2O. The Raman spectrum of akimotoite

Z674 in the OH region is shown in Fig. 2. We observe

three bands, at 3,295, 3,320, and 3,350 cm-1, respectively.

The signal-to-noise ratio (SNR) for the OH band at

3,350 cm-1 was calculated using SNR = S/ry, where S is

the average signal peak height above the background and

ry is the standard deviation of the peak height (McCreery

2005). For the spectrum, we obtain SNR *20. Because

sample Z674 contains about 550 ppm wt H2O (from FTIR

above), the SNR suggests that sample SH1101 contains

less than *30 ppm wt H2O, based upon the lack of

observed Raman modes in the 3,300–3,400 cm-1 region.

Therefore, we conclude from Raman spectroscopy that

akimotoite SH1101 is nominally anhydrous.

FTIR at high-P and low-T

Low-temperature vibrational spectra at 10-4 Pa and over

three different high-pressure ranges at 21–28, 11–16, and

5.5–10 GPa were collected from 15 to 300 K. We observe

three OH bands throughout the measurements, with 300 K

frequencies of about 3,300, 3,320, and 3,388 cm-1. These

OH bands shift to higher frequencies upon decreasing tem-

perature, with average shifts of -0.0039, -0.0049 and

-0.046 (cm K)-1in the range of 15–300 K (Fig. 5). We

Table 1 Intensity data collection parameters and refined atomic position coordinates for akimotoite samples Z674 and SH1101

Z674 SH1101 Z674 SH1101

a (A) 4.7283(6) 4.7295(3) R1 for I [ 4r (%): 2.96 3.58

c (A) 13.560(2) 13.560(1) Rint (%): 1.98 1.85

Vol. (A3) 262.55(6) 262.68(4)

No. total refl.: 925 1,092 Mga z: 0.36001(6) 0.35999(8)

No. unique total: 254 270 Sia Z: 0.15777(4) 0.15768(6)

No. unique

I [ 4r:

235 O x: 0.3222(2) 0.3222(3)

GooF: 0.819 0.930 y: 0.0370(2) 0.0367(3)

z: 0.24008(6) 0.24011(8)

a: x = y = 0 for Mg and Si coordinates

Table 2 Anisotropic displacement parameters (A2) for Z674 and

SH1101

Z674 SH1101 Z674 SH1101

Mga U11: 0.0067(4) 0.0092(5) O U11: 0.0050(5) 0.0072(6)

U33: 0.0083(4) 0.0068(6) U22: 0.0053(5) 0.0077(6)

U12: 0.0034(2) 0.0046(2) U33: 0.0066(5) 0.0067(6)

Ueq: 0.0073(3) 0.0084(4) U23: 0.0008(3) 0.0008(4)

Sia U11: 0.0053(3) 0.0077(4) U13: 0.0001(3) 0.0000(4)

U33: 0.0068(4) 0.0057(4) U12: 0.0020(3) 0.0032(4)

U12: 0.0026(2) 0.0039(2) Ueq: 0.0059(3) 0.0074(4)

Ueq: 0.0058(3) 0.0071(3)

a U22 = U11; U23 = U13 = 0 for Mg and Si


123

observed a significant sharpening of 3,389 cm-1 band from

21 cm-1 (300 K) to 12 cm-1 (15 K) FWHM at ambient

pressure (Fig. 4a), with less than 10 % narrowing of the

other two bands. The sharp 3,700 cm-1 peaks in Fig. 4a

suggest micro-inclusions of brucite inside the hydrous

akimotoite sample, which were also observed in Raman

spectra and reported by Bolfan-Casanova et al. (2002). Peaks

between 2,800 and 3,000 cm-1 may be due to the diamond.

Upon decompression from high-pressure, we find steep

room temperature frequency shifts with pressure (dm/dP) of

-10, -8.2, and -11.4 (cm GPa-1) (Fig. 6). The three

bands become very broad and overlap at 21–25.5 GPa at all

temperatures (Fig. 4d). However, upon cooling from 300 to

10 K at pressures from 10.8 to 13.6, the three OH bands

can be resolved except at 10 K. (Fig. 4c). Upon cooling at

5.4–7.5 GPa, the three OH bands become more clearly

resolved, but still overlap (Fig. 4b).

The sample pressure increased upon cooling due to

thermal contraction of the diamond cell, and thus, the

measured frequency shifts are therefore a consequence of

both changing temperature and pressure. Assuming that the

pressure dependence is independent of temperature, we

determine larger temperature dependence of the frequency

increases with increasing pressure.

The frequency shifts for the 3,300, 3,320, and 3,388 cm-1

bands are -0.21(1) (cm K)-1, -0.19(1) (cm K)-1, and

-0.206(4) (cm K)-1 at 5.5 GPa, respectively, while

-0.16(3), -0.12(2), and -0.17(5) (cm K)-1 at 10–13 GPa,

respectively. Due to overlapping bands at higher pressure, it

is more difficult to resolve the temperature dependence.

With both pressure and temperature dependence of the

OH vibrational modes in akimotoite, along with thermal

expansion and bulk modulus measurements on the same

sample, it is then possible to calculate the isobaric and

isothermal mode Gruneisen parameters as in Eqs. (1, 2),

respectively,

ci;P ¼1

ao ln mi

oT

� �P

ð1Þ

Fig. 5 Variation in vibrational frequencies with temperature at room

pressure for the three OH bands of Z674

Fig. 6 Variation in vibrational frequencies with pressure and

temperature for the three OH bands in OH-akimotoite sample Z674


123

ci;T ¼ KT

o ln mi

oP

� �T

ð2Þ

The intrinsic anharmonic mode parameter, ai, can therefore

be derived from these values,

ai ¼ a ci;T � ci;P

� �¼ aKT

o ln mi

oP

� �T

� o ln mi

oT

� �P

¼ o ln mi

oT

� �V

ð3Þ

Given the volume thermal expansion coefficient

a0_V = 14.8(9) 9 10-6 K-1 (153–300 K) and isothermal

bulk modulus KT = 217(3) GPa (BM2 EoS), we reported

the isobaric and isothermal mode Gruneisen parameters

(Eqs. 1, 2), as well as the intrinsic anharmonic mode

parameter for the samples Z674 (*550 ppm wt H2O)

(Eq. 3) in Table 3.

The negative intrinsic anharmonic mode parameters for

the 3,300.6 and 3,320.2 cm-1 vibrational modes indicate

relatively weak bonding in the OH��O in the akimotoite

structure, comparable to the external XO6 and Mg trans-

lational modes in akimotoite (Okada et al. 2008). The

positive intrinsic anharmonic mode parameter for

3,387.5 cm-1 is comparable to the values for internal

vibrational modes in akimotoite, indicative of strong bonds

through long O–O distances, consistent with the higher

vibrational frequency.

Crystal structures

The crystal structure of akimotoite (space group R 3) has a

distorted hexagonal close packing (HCP) of oxygen anions

with Mg2? and Si4? cations occupying octahedral sites

(Horiuchi et al. 1982). The MgO6 and SiO6 octahedra form

alternating layers along the c axis, and the cations are

completely ordered if each layer contains only Mg or only

Si, so that the closest pairs of cations in the face-sharing

octahedra are always Mg–Si. The bond lengths and poly-

hedral volumes of cation polyhedral for the current akim-

otoite samples of Z674 and SH1101 are calculated using

the software package XTALDRAW (Downs et al. 1993)

and listed in Table 4, compared with those from Horiuchi

et al. (1982). The Mg–O, Si–O bond lengths and octahedral

volumes of the current samples are identical with each

other, in spite of the different H2O contents, indicating that

such small water contents have no significant impact on the

crystal structures.

Although the unit-cell volumes of the two samples are

identical within error to each other and to the previous

results of Horiuchi et al. (1982), the oxygen position

parameters differ significantly from those of the previous

study giving the current samples a slightly larger Mg and

slightly smaller Si octahedron. The\Mg–O[and\Si–O[lengths of akimotoite from Horiuchi et al. (1982) are

0.4(1) % smaller and 1.0(1) % larger, respectively, than

those of the current samples, indicating that the sample from

Horiuchi et al. (1982) might not be completely ordered.

Since Mg2? cation has a larger radius than Si4?, even a

small portion of Mg and Si sites exchange could reduce the

measured Mg–O lengths, while increase the measured Si–O

lengths without changing the structure of R 3. This would be

consistent with a more complete ordering of the cation in

the current samples. The durations of the heating cycles for

the current samples were 8 and 4 h, respectively, whereas

that of the sample studied by Horiuchi et al. (1982) was only

20 min, at the experimental conditions of 22 GPa and

1,550 �C, which were similar to those of the current sam-

ples. On the other hand, both the samples of Z674 and

SH1101 share nearly identical internal structures, indicating

that small water contents of *500 ppm wt have no sig-

nificant impact on the crystal structure of akimotoite.

Table 3 Isobaric and isothermal mode Gruneisen parameters and intrinsic anharmonic mode parameter for hydrous MgSiO3 akimotoite samples

of Z674 and Bolfan-Casanova et al. (2002)

Frequency at ambient

condition (cm-1)

Z674 Bolfan-Casanova

et al. (2002)

ci,Pa ci,T

b ai (10-5 K-1) ci,pc

3,300.6 -0.12(2) -0.45(12) -1.02(12) -0.32

3,320.2 -0.06(3) -0.37(10) -0.96(10) -0.42

3,387.5 -1.1(2) -0.55(11) 1.7(2) -0.41

a At 0 GPa, b up to 11 GPa, c up to 10 GPa

Table 4 Bond lengths (A) and polyhedral volumes (A3) of cation

polyhedral for akimotoite

Z674 SH1101 Horiuchi et al. (1982)

Mg O 9 3: 2.175(1) 2.175(1) 2.163(2)

O 9 3: 1.994(1) 1.993(1) 1.990(2)

\Mg–O[: 2.084(1) 2.084(1) 2.076(2)

Poly. Vol.: 11.35(1) 11.35(1) 11.24(2)

Si O 93: 1.825(1) 1.827(1) 1.830(2)

O 93: 1.760(1) 1.761(1) 1.768(2)

\Si–O[: 1.793(1) 1.794(1) 1.799(2)

Poly. Vol.: 7.51(1) 7.52(1) 7.59(1)


123

Thermal expansion

Temperature variation in the lattice parameters and unit-

cell volume for sample Z674 (*550 ppm wt H2O) nor-

malized to 300 K are plotted in Fig. 7, compared with

those of anhydrous MgSiO3 akimotoite from Ashida et al.

(1988). The fitted curves indicate that the slope of a versus

T for Z674 is slightly larger than reported by Ashida et al.

(1988), whereas the slope of c versus T for Z674 is slightly

smaller. The linear temperature-dependent expansion

coefficients a1 and a0, as well as average thermal expansion

coefficient (a0) for Z674, are summarized in Table 5,

compared with Ashida et al. (1988). a0(V) for sample Z674

is 29.0(2) 9 10-6 K-1 (300–839 K), 19 % larger than

previous results from Ashida et al. (1988), and a0(c) is

*30 % larger than a0(a) for sample Z674, while *50 %

larger for Ashida et al. (1988). Hence, according to these

two samples of akimotoite, hydration slightly increases

bulk thermal expansivity and decreases the anisotropy of

axial thermal expansivities.

The c/a ratio versus temperature for sample Z674 is

plotted in Fig. 8. The c/a ratio thus increases with tem-

perature because of larger thermal expansion in c direction.

Conversely, the positive slope becomes smaller with tem-

perature because a1(a) is significantly larger than a1(c)

for the temperature-dependent coefficients. Here, we fit the

c/a ratio as a second-order polynomial function of T as in

Eq. (4):

c=a ¼ 2:8625 8ð Þ þ 2:0 3ð Þ � 10�5 � T � 1:3 3ð Þ� 10�8 � T2 ð4Þ

It is important to notice that the change in unit-cell

parameters for Z674 is not significant after heating to

839 K, compared with the uncertainties of a, c, V. There

are no obvious differences of unit-cell parameters and

internal structures between anhydrous and hydrous

(550 ppm wt H2O) akimotoite samples, as discussed in the

previous part of crystal structures. Hence, X-ray is not an

efficient method to determine whether dehydration hap-

pened or not in this study.

Isothermal compressibility

Variations in the unit-cell volumes with pressure for

akimotoite samples of Z674, Wang et al. (2004) and

Reynard et al. (1996) are plotted in Fig. 9, with second-

order Birch–Murnaghan equation of state (BM2 EoS) fit-

ting for each data set. The BM2 fitting results are listed in

Table 6, compared with the theoretical values from Karki

and Wentzcovitch (2002) and Da Silva et al. (1999). For

sample Z674, the calculated V0 from BM2 is 263.7(2) A3,

0.4 % larger than the value measured in our laboratory,

which can be attributed to the systematic difference

between two experimental set ups in Sector 13, APS, and

our laboratory (Ye et al. 2010, 2012). For BM2 EoS fit-

tings, the KT value from Reynard et al. (1996) is signifi-

cantly larger than that from this study, and Reynard et al.

(1996) adopted pure H2O as the pressure-transmitting

medium, which transforms to the ice-VII polymorph above

2.3 GPa. The KT value from Wang et al. (2004) is slightly

larger than the current value, which is consistent with the

previous conclusion that the bulk thermal expansion coef-

ficient of this study is slightly larger than that from Wang

et al. (2004). The variation in densities with pressure (up to

20 GPa) for samples of Z674, Wang et al. (2004) and

Reynard et al. (1996) is shown in Fig. 10. For this pressure

range up to 20 GPa, linear regressions are adopted to

demonstrate how densities decrease as functions of pres-

sure (to the first order of approximation), with slopes of

0.0157(1) g/(cm3 GPa) (R2 = 0.9993) for sample Z674,

0.0150(2) g/(cm3 GPa) (R2 = 0.9993) for Wang et al.

(2004), and 0.0152(3) g/(cm3 GPa) (R2 = 0.9993) for

Reynard et al. (1996). The slope for sample Z674 is larger

than those of anhydrous samples from Wang et al. (2004)

and Reynard et al. (1996). This is also consistent with the

current sample being slightly more compressible than the

anhydrous ones presumably due to Mg2? vacancies asso-

ciated with the *550 ppm wt H2O content of the sample.

In addition, third-order BM EoS fitting for sample Z674

gives V0 = 263.4(2) A3, KT0 = 235(9) GPa, K0 = 2.7(6).

K0 is significantly smaller than 4. The results of sample

Z674 for both third-order and second-order B-M EOS fit-

tings are plotted in Fig. 11 with confidence ellipsoids for

68.3, 90, and 95.4 % (Angel 2000), and the point for sec-

ond-order fitting is on the ellipsoid for 90 %.

The a and c axes versus pressure are plotted in Fig. 12,

and the axial compressibilities are summarized in Table 6.

100 200 300 400 500 600 700 800 9000.996

0.998

1.000

1.002

1.004

1.006

1.008

1.010

1.012

1.014

1.016

1.018a/a

0

c/c0

V/V0

2nd-order polynomial fits for Z674 linear fits for Ashida et al. (1988)

X/X

0

T (K)

Fig. 7 Fractional unit-cell parameters versus temperature for sample

Z674 (solid symbols 153–839 K) and Ashida et al. (1988) (open

symbols 298–820 K). The two sets of unit-cell parameters at

temperatures are normalized to room temperature


123

The results from Reynard et al. (1996) and Wang et al.

(2004) are consistent with each other, while the axial

compressibilities of the current sample are 11(3) % larger

in a direction and 11(2) % smaller in c direction, compared

with those of Wang et al. (2004). On the other hand, all

three studies are consistent in having the c axis more

compressible than the a axis: bc/ba ratios are 1.39(5),

1.73(9), and 1.82(4) for this study, Wang et al. (2004) and

Reynard et al. (1996) respectively. The anisotropy of axial

compressibilities is consistent with the anisotropy of axial

thermal expansion, discussed above. Further, this is con-

sistent with the conclusion that longitudinal moduli

C33 \ C11 from elasticity studies of akimotoite (Li et al.

2009; Weidner and Ito 1985) and the observation that

P-wave anisotropies of akimotoite single crystal have

minimum value in the c direction by the crystallographic

preferred orientation studies of Shiraishi et al. (2008) and

Zhang et al. (2005). The c/a ratios versus pressure are

plotted in Fig. 13. For this study, the c/a ratio is linearly

fitted as in Eq. (5):

c=a ¼ 2:8700 9ð Þ � 0:0017 1ð Þ � P GPað Þ ð5Þ

The linear regression slopes for c/a versus P are

-0.0019(3) for Wang et al. (2004) and -0.0026(1) for

Reynard et al. (1996), both of which are larger in absolute

values compared with that of the current study, because of

the larger bc/ba ratios. Hence, hydration decreases the

anisotropy of axial compressibilities, as well as axial

thermal expansivities discussed above.

There are several previous studies reporting isothermal

compressibilities of MgSiO3 polymorphs (Hugh-Jones and

Angel 1994 for orthoenstatite; Hazen et al. 1994 for maj-

orite; Wang et al. 2004 for akimotoite; Ross and Hazen

1990 for perovskite, etc.), as well as Mg2SiO4 polymorphs

(e.g., Couvy et al. 2010 for forsterite; Holl et al. 2008 for

wadsleyite; Ye et al. 2012 for ringwoodite, etc.). In addi-

tion, the H2O contents can be up to *3 wt% in wadsleyite

(e.g., Inoue et al. 1995) and ringwoodite (e.g., Ye et al.

2012). Hydration has a significant effect on decreasing the

bulk moduli and densities of these materials (Holl et al.

2008; Jacobsen and Smyth 2006; Ye et al. 2012, etc.). Here,

the isothermal bulk moduli KT values for MgSiO3 poly-

morphs, as well as anhydrous and hydrous Mg2SiO4 poly-

morphs, are plotted against density q in Fig. 14, with linear

regressions for MgSiO3 and Mg2SiO4 polymorphs, respec-

tively. All KT values are derived by second-order B-M EoS

fitting with K0 fixed at 4, for better investigation of

Table 5 Volume and axial thermal expansion coefficients for akimotoite Z674 (153–839 K), compared with those from Ashida et al. (1988)

(298–820 K)

a = a1 9 T ? a0 Ashida et al. (1988)

a1 (10-9 K-2) a0 (10-6 K-1) R2 a0 (10-6 K-1) R2 a0 (10-6 K-1) R2

V 20(3) 17(2) 0.9980 27.1(6) 0.9929 24.4(9) 0.9342

a 10(1) 3.4(8) 0.9957 8.2(3) 0.9831 7.1(6) 0.8970

c 1(1) 10.1(5) 0.9991 10.68(9) 0.9990 10.0(7) 0.8963

2.864

2.865

2.866

2.867

2.868

2.869

2.870

2.871

2.872

c / a

T (K)100 200 300 400 500 600 700 800 900

Fig. 8 Variation in the c/a axial with temperature for OH-akimotoite

sample Z674 with second-order polynomial regression

0 5 10 15 20 25 30 35230

235

240

245

250

255

260

265 Z674 Wang et al. (2004) T0150 Wang et al. (2004) T0133 Reynard et al. (1996) Fitting for Z674 Fitting for Wang et al. (2004) Fitting for Reynard et al. (1996)

V(Å

3 )

P (GPa)

Fig. 9 Unit-cell volumes versus pressure with the fitting curves with

BM2 EoS fitting


123

relationship between KT and q. There are some discrepan-

cies among the compressibility studies for perovskite, and

the results from Ross and Hazen (1990), Yagi et al. (1982)

are significantly lower than the linear fitting trend. The

linear regression for MgSiO3 and Mg2SiO4 polymorphs is

expressed in Eqs. (6) and (7), respectively:

MgSiO3 : KT GPað Þ ¼ 162 5ð Þ � q g=cm3� �

� 401 11ð ÞR2 ¼ 0:9901� �

ð6Þ

Mg2SiO4 : KT GPað Þ ¼ 170 7ð Þ � q g=cm3� �

� 421 18ð ÞR2 ¼ 0:9813� �

ð7Þ

According to Fig. 14, hydration decreases both densities

and bulk moduli for wadsleyite and ringwoodite, but still

obeys the linear relationship (Eq. 7). This is consistent with

the conclusion from Mookherjee and Stixrude (2009) that

hydrous Mg2SiO4 polymorphs tend to obey Birch’s law

nearly as well as anhydrous ones, which establishes the

compressional wave velocity Vp is linearly dependent of

the density.

In summary, our experiments support the following:

1. Both hydrous (Z674) and anhydrous (SH1101)

MgSiO3 akimotoite samples were synthesized under

multi-anvil pressure, simulating the high-pressure and

temperature conditions of the lower transition zone.

The FTIR and Raman spectra at ambient condition

indicate the water contents are *550 ppm wt for

sample Z674 and \50 ppm wt for SH1101.

2. High-pressure low-temperature FTIR experiments

were conducted for sample Z674 to derive the isobaric

and isothermal mode Gruneisen parameters

(0–11 GPa, 10–300 K) as well as the intrinsic anhar-

monic mode parameters at 3,300, 3,321, and

3,389 cm-1.

3. Single-crystal X-ray diffraction studies demonstrate

that both the samples Z674 and SH1101 share nearly

identical unit-cell parameters and internal structure,

implying such small water contents have no significant

effect on the akimotoite crystal structure. Both the

current samples have larger \Mg–O[ while smaller

\Si–O[ than Horiuchi et al. (1982), meaning the

Table 6 Isothermal bulk moduli and axial compressibilities (10-4 GPa) for akimotoite

KT (GPa) K0 V0 (A3)a ba bc Pmax (GPa)

Z674 217(3) 4 263.7(2) 11.4(3) 15.9(3) 34.6

Wang et al. (2004) 221(4) 4 264.1(3) 10.3(4) 17.8(6) 17.0

Reynard et al. (1996) 227(7) 4 262.0(3) 10.0(2) 18.2(2) 25.2

Karki and Wentzcovitch (2002)b 201 4.64

Da Silva et al. (1999)c 222 4.5

a Volume values are derived from BM2 EoS fittingsb Calculated from first-principals lattice dynamicsc Adiabatic bulk modulus calculated from ab initio study of the elastic behavior

0 5 10 15 20

3.80

3.85

3.90

3.95

4.00

4.05

4.10 Wang et al. (2004) T0150 Wang et al. (2004) T0133 Reynard et al. (1996) This study

(g/c

m3 )

P (GPa)

ρ

Fig. 10 Variation in density with pressure for OH-akimotoite sample

Z674 (solid squares) compared with other studies

Fig. 11 Confidence ellipsoid plots for K0 versus KT0 from B-M EOS

fittings, with error bars for the point from third-order Birch–

Murnaghan equation of state fitting


123

current structures are more ordered, due to longer

reaction time during synthetic process.

4. The hydrous sample Z674 has a larger thermal

expansivity and compressibility than the anhydrous

ones (Wang et al. 2004; Ashida et al. 1988; Reynard

et al. 1996), indicating that hydration could soften

MgSiO3 akimotoite, as it softens Mg2SiO4 polymorphs

(e.g., Holl et al. 2008; Ye et al. 2009, 2010, 2012).

5. In akimotoite structure, the c direction has larger

thermal expansivity and compressibility than the

a direction, causing c/a ratio increasing with increased

temperature while decreasing with increased pressure.

On the other hand, hydration would decrease the

anisotropies of axial thermal expansivity and

compressibility.

Acknowledgments This work was supported by US National Sci-

ence Foundation Grants EAR 11-13369 to JRS, EAR-0748707

(CAREER) to SDJ, and EAR-0955647 (CAREER) to WRP. We also

acknowledge the support from Carnegie/DOE Alliance Center

(CDAC) and the David and Lucile Packard Foundation. Synthesis was

carried out at Bayerisches Geoinstitut (BGI), through support of the

BGI Visitors Program. Neal Blair is acknowledged for access to the

FTIR microscope at Northwestern University. GeoSoilEnviroCARS

was supported by the NSF (EAR-0622171), the Department of Energy

(DOE) DE-FG02-94ER14466, and the State of Illinois. Use of the

Advanced Photon Source was supported by the DOE Office of Sci-

ence, Office of Basic Energy Sciences, Under Contract No. DE-

AC02-06CH11357. The use of the U2A beamline at the National

Synchrotron Light Source beamline was supported by COMPRES,

through the NSF Cooperative Agreement EAR 06-49658 and by the

DOE, Office of Science, Office of Basic Energy Sciences, under

Contract No. DE-AC02-98CH10886.

Appendix 1

See Table 7.

0 5 10 15 20 25 30 350.940

0.945

0.950

0.955

0.960

0.965

0.970

0.975

0.980

0.985

0.990

0.995

1.000

1.005

Z674 (dark: a axis; gray: c axis) run T0150 Wang et al. (2004) run T0133 Wang et al. (2004) Reynard et al. (1996) fitting line for current data fitting line for Reynard et al. (1996)

c/c0

X /

X0

P (GPa)

a/a0

Fig. 12 Variation in the normalized lattice parameters with pressure

for OH-akimotoite sample Z674, with a0 = 4.726(2) A,

c0 = 13.567(3) A

0 5 10 15 20 25 30 35

2.80

2.81

2.82

2.83

2.84

2.85

2.86

2.87

2.88

c/a

P (GPa)

Z674run T0150 Wang et al. (2004)run T0133 Wang et al. (2004) Reynard et al. (1996) fitting line for Z674

fitting line for Reynard et. (1996)

Fig. 13 Variation in axial c/a ratio with pressure for akimotoite

3.2 3.4 3.6 3.8 4.0 4.2

80

100

120

140

160

180

200

220

240

260

280

300

320forstertite wadsleyiteringwooditeperovskite akimotoitemajoriteHigh-P clinoenstatiteLow-P clinoenstatiteorthoenstatite

KT

0 (G

Pa)

(g/cm3ρ )

MgSiO3

Mg2SiO

4

Fig. 14 Isothermal bulk modulus KT (K0 fixed at 4) versus density qfor MgSiO3 and Mg2SiO4 polymorphs, with linear regressions (dash

lines), respectively. (enstatite: Hugh-Jones and Angel 1994; low-

P and high-P clinoenstatite: Jacobsen et al. 2010; majorite: Hazen

et al. 1994; akimotoite: this study, Wang et al. 2004; Reynard et al.

1996; perovskite: Ross and Hazen 1990; Yagi et al. 1982; Knittle and

Jeanloz 1987; Mao et al. 1989; forsterite: Couvy et al. 2010;

wadsleyite: Holl et al. 2008; Yusa and Inoue 1997; Ye et al. 2010;

ringwoodite: Hazen 1993; Yusa et al. 2000; Ye et al. 2012)


123

Appendix 2

See Table 8.

Appendix 3

See Table 9.

References

Angel RJ (2000) Equations of state. In: Hazen RM, Downs RT (eds)

High-pressure and high-temperature crystal chemistry, MSA.

Rev Mineral Geochem 41:35–60

Ashida T, Kume S, Ito E, Navrotsky A (1988) MgSiO3 ilmenite: heat

capacity, thermal expansivity, and enthalpy of transformation.

Phys Chem Miner 16:239–245

Bolfan-Casanova N, Keppler H, Rubie DC (2002) Hydroxyl in

MgSiO3 akimotoite: a polarized and high-pressure IR study. Am

Mineral 87:603–608

Couvy H, Chen J, Drozd V (2010) Compressibility of nanocrystalline

forsterite. Phys Chem Miner 37:343–351

Table 7 OH frequencies (cm-1) for akimotoite Z674 at pressures

and temperatures

P (GPa) T (K) OH frequencies (cm-1)

Cooling cycle 1

21.3 300 3259.1

250

23.9 200 3,220.5 3,264.9 3,301.5

25.7 150 3,257.2

27 100 3,237.9 3,266.8

27.8 50 3,226.3 3,264.9

28.2 15 3,228.2 3,264.9

Cooling cycle 2

10.8 300 3,226.3 3,261 3,297.7

12.5 250 3,226.3 3,263 3,295.7

13.8 200 3,230.2 3,268.7 3,307.3

14.7 150 3,234 3,266.8 3,318.9

15.7 100 3,247.5 3,274.5

16.2 50 3,226.3 3,264.9

16.3 15 3,236 3,266.8 3,313.1

Cooling cycle 3

5.44 300 3,245.6 3,276.5 3,326.6

7.2 250 3,237.9 3,274.5 3,317

8.1 200 3,239.8 3,274.5 3,317

8.8 150 3,237.9 3,278.4 3,318.9

9.6 100 3,245.6 3,286.1 3,322.7

10.2 50 3,251.4 3,290 3,324.7

10.2 15 3,257.2 3,291.9 3,330.5

Cooling cycle 4 (different sample fragments)

0 300 3,300.6 3,320.2 3,387.5

0 250 3,300.9 3,320.5 3,390.2

0 200 3,301.1 3,320.3 3,393

0 150 3,301.5 3,320.5 3,396.5

0 100 3,300.6 3,320.65 3,399.4

0 50 3,302.3 3,321.84 3,400

0 15 3,301.6 3,321.4 3,399.4

Table 8 Unit-cell parameters of akimotoite Z674 as functions of

temperature

T (K) a (A) c (A) V (A3)

153(2) 4.7264(5) 13.542(2) 261.96(5)

203(2) 4.7269(5) 13.546(2) 262.12(5)

253(2) 4.7276(6) 13.552(2) 262.31(6)

300(2) 4.7283(5) 13.560(2) 262.54(6)

349(3) 4.7306(6) 13.568(2) 262.94(6)

395(3) 4.7320(5) 13.575(2) 263.26(5)

Table 9 Unit-cell parameters of akimotoite Z674 as functions of

pressure

P (GPa) a (A) c (A) V (A3)

1.38(2) 4.722(4) 13.559(5) 261.9(3)

2.02(4) 4.717(3) 13.535(4) 260.8(3)

2.81(9) 4.719(2) 13.502(3) 260.4(2)

3.92(9) 4.712(3) 13.474(3) 259.1(2)

5.77(6) 4.694(4) 13.467(5) 257.0(3)

9.01(6) 4.686(3) 13.373(4) 254.3(2)

11.54(8) 4.672(3) 13.321(4) 251.8(2)

13.91(7) 4.656(5) 13.257(6) 248.8(4)

16.00(7) 4.647(4) 13.208(6) 247.1(3)

18.54(5) 4.639(5) 13.156(6) 245.2(4)

20.53(8) 4.633(3) 13.121(4) 243.9(2)

21.84(8) 4.616(3) 13.099(4) 241.7(2)

26.62(5) 4.601(4) 13.001(5) 238.3(3)

29.40(9) 4.590(5) 12.963(6) 236.5(4)

30.88(7) 4.581(5) 12.942(7) 235.2(4)

34.46(7) 4.576(3) 12.839(4) 232.9(2)

Table 8 continued

T (K) a (A) c (A) V (A3)

440(4) 4.7338(7) 13.581(3) 263.56(7)

483(4) 4.7355(7) 13.586(3) 263.86(7)

537(4) 4.7379(8) 13.594(3) 264.27(7)

586(4) 4.7405(6) 13.603(2) 264.73(6)

632(5) 4.7426(6) 13.607(2) 265.05(6)

681(5) 4.7443(6) 13.617(2) 265.42(6)

736(5) 4.7464(6) 13.625(2) 265.83(6)

782(5) 4.7485(5) 13.631(2) 266.18(5)

839(5) 4.7519(5) 13.639(2) 266.71(5)


123

Cromer DT, Mann J (1968) X-ray scattering factors computed from

numerical Hartree–Fock wave functions. Acta Crystallogr

A24:321–325

Da Silva CRS, Karki BB, Stixrude L, Wentzcovitch RM (1999) Ab

initio study of the elastic behavior of MgSiO3 ilmenite at high

pressure. Geophys Res Lett 26(7):943–946

Dera P (2007a) GSE-ADA data analysis program for monochromatic

single crystal diffraction with area detector. GeoSoilEnviro-

CARS, Argonne

Dera P (2007b) RSV reciprocal space viewer program for single

crystal data analysis. GeoSoilEnviroCARS, Argonne

Dorogokupets PI, Dewaele A (2007) Equations of state of MgO, Au,

Pt, NaCl-B1 and NaCl-B2: internally consistent high-tempera-

ture pressure scales. High Press Res 27:431–436

Downs RT, Bartelmehs KL, Gibbs GV, Boisen MB (1993) Interactive

software for calculating and displaying X-ray or neutron powder

diffractometer patterns of crystalline materials. Am Mineral

78:1104–1107

Farrugia LJ (1999) WinGX software package. J Appl Crystallogr

32:837–838

Gasparik T (1990) Phase relations in the transition zone. J Geophys

Res 95:15751–15769

Hazen RM (1993) Comparative compressibilities of silicate spinels:

anomalous behavior of (Mg, Fe)2SiO4. Science 259:206–209

Hazen RM, Downs RT, Conrad PG, Finger LW, Gasparik T (1994)

Comparative compressibilities of majorite-type garnets. Phys

Chem Miner 21:344–349

Holl CM, Smyth JR, Jacobsen SD, Frost DJ (2008) Effects of

hydration on the structure and compressibility of wadsleyite,

b-(Mg2SiO4). Am Mineral 93:598–607

Horiuchi H, Hirano M, Ito E, Matsui Y (1982) MgSiO3 (ilmenite-type):

single crystal X-ray diffraction study. Am Mineral 67:788–793

Hugh-Jones DA, Angel RJ (1994) A compressional study of MgSiO3

orthoenstatite up to 8.5 GPa. Am Mineral 79:405–410

Inoue T, Yurimoto H, Kudoh Y (1995) Hydrous modified spinel,

Mg1.75SiH0.5O4: a new water reservoir in the mantle transition

region. Geophys Res Lett 22:117–120

Ito E, Matsui Y (1977) Silicates ilmenites and the post-spinel

transformations. In: Manghnani and Akimoto S (eds) High Press

Res Appl Geophys. Academic Press, New York, pp 193–206

Jacobsen SD, Smyth JR (2006) Effect of water on the sound velocities of

ringwoodite in the transition zone. In: Jacobsen SD, van der Lee S

(eds) Earth’s deep water cycle, vol 168., American Geophysical

Union Monograph SeriesAGU, Washington, pp 131–145

Jacobsen SD, Liu Z, Boffa-ballaran T, Littlefield EF, Ehm L, Hemley

RJ (2010) Effect of H2O on upper mantle phase transitions in

MgSiO3: is the depth of the seismic X-discontinuity an indicator

of mantle water content? Phys Earth Planet Int 183:234–244

Karki BB, Wentzcovitch RM (2002) First-principles lattice dynamics

and thermoelasticity of MgSiO3 ilmenite at high pressure.

J Geophys Res 107(B11):2267. doi:10.1029/2001JB000702

Knittle E, Jeanloz R (1987) Synthesis and equation of state of (Mg,

Fe)SiO3 perovskite to over 100 Gigapascals. Science 235:668–670

Kuroda K, Irifune T, Inoue T, Nishiyama N, Miyashita M, Funakoshi K,

Utsumi W (2000) Determination of the phase boundary between

ilmenite and perovskite in MgSiO3 by in situ X-ray diffraction and

quench experiments. Phys Chem Miner 27:523–532

Li L, Weidner DJ, Brodholt J, Alfe D, Price GD (2009) Ab initio

molecular dynamics study of elasticity of akimotoite MgSiO3 at

mantle conditions. Phys Earth Planet Int 173:115–120

Libowitzky E, Rossman GR (1997) An IR absorption calibration for

water in minerals. Am Mineral 82:1111–1115

Mao HK, Hemley RJ, Shu J, Chen L, Jephcoat AP, Bassett WA

(1989) The effect of pressure, temperature, and composition on

lattice parameters and density of (Mg, Fe)SiO3-perovskite to 30

GPa. Annu Rep Dir Geophys Lab 1988–1989:82–89

McCreery RL (2005) Signal-to-noise in Raman spectroscopy. In:

Winefordner JD (ed) Raman spectroscopy for chemical analysis.

John Wiley & Sons, Inc., Hoboken, NJ, USA. doi:10.1002/

0471721646.ch4

Mookherjee M, Stixrude L (2009) Structure and elasticity of

serpentine at high-pressure. Earth Planet Sci Lett 279:11–19

Okada T, Narita T, Nagai T, Yamanaka T (2008) Comparative Raman

spectroscopic study on ilmenite-type MgSiO3 (akimotoite),

MgGeO3, and MgTiO3 (geikielite) at high temperatures and

high pressures. Am Mineral 93:39–47

Patterson MS (1982) The determination of hydroxyl by infrared

absorption in quartz, silicate glasses and similar materials. Bull

Mineral 105:20–29

Reynard B, Fiquet G, Itie J-P, Rubie DC (1996) High-pressure X-ray

diffraction study and equation of state of MgSiO3 ilmenite. Am

Mineral 81:45–50

Rivers M, Prakapenka VB, Kubo A, Pullins C, Holl CM, Jacobsen SD

(2008) The COMPRES/GSECARS gas-loading system for

diamond anvil cells at the Advanced Photon Source. High Press

Res 28:273–292

Ross NL, Hazen RM (1990) High-pressure crystal chemistry of

MgSiO3 perovskite. Phys Chem Miner 17:228–237

Sawamoto H (1987) Phase diagram of MgSiO3 at pressures up to 24

GPa and temperatures up to 2200 �C: phase stability and

properties of tetragonal garnet. In: Manghnani MH, Syono Y

(eds) High Press Res Miner Phys. American Geophysical Union,

Washington, pp 209–219

Sheldrick GM (1997) SHELXL97, Release 97-2. Program for the

refinement of crystal structures. University of Gottingen, Gottingen

Shiraishi R, Ohtani E, Kanagawa K, Shimojuku A, Zhao D (2008)

Crystallographic preferred orientation of akimotoite and seismic

anisotropy of Tonga slab. Nature 455:657–660

Tokonami M (1965) Atomic scattering factor for O2-. Acta

Crystallogr 19:486

Wang Y, Uchida T, Zhang J, Rivers ML, Sutton SR (2004) Thermal

equation of state of akimotoite MgSiO3 and effects of the

akimotoite-garnet transformation on seismic structure near the

660 km discontinuity. Phys Earth Planet Int 143–144:57–80

Weidner D, Ito E (1985) Elasticity of MgSiO3 in the ilmenite phase.

Phys Earth Planet Int 40:65–70

Kato T, Ohtani E, Morishima H, Yamazaki D, Suzuki A, Suto M,

Kubo T (1995) In situ X-ray observation of high-pressure phase

transitions of MgSiO3 and thermal expansion of MgSiO3

perovskite at 25 GPa by double-stage multianvil system. J Geo-

phys Res 100(B10):20475–20481

Yagi T, Mao HK, Bell PM (1982) Hydrostatic compression of

perovskite-type MgSiO3. In: Saxena SK (ed) Advances in

physical geochemistry. Springer, Berlin, pp 317–325

Ye Y, Schwering RA, Smyth JR (2009) Effects of hydration on

thermal expansion of forsterite, wadsleyite, and ringwoodite at

ambient pressure. Am Mineral 94:899–904

Ye Y, Smyth JR, Hushur A, Manghnani MH, Lonappan D, Dera P, Frost

DJ (2010) Crystal structure of hydrous wadsleyite with 2.8 % H2O

and compressibility to 60 GPa. Am Mineral 95:1765–1772

Ye Y, Brown DA, Smyth JR, Panero WR, Chang Y-Y, Jacobsen SD,

Townsend J, Thomas S-M, Hauri EH, Dera P (2012) Compress-

ibility and thermal expansion of hydrous ringwoodite with

2.5(3) wt% H2O. Am Mineral 97:573–582

Yusa H, Inoue T (1997) Compressibility of hydrous wadsleyite (b-

phase) in Mg2SiO4 by high pressure X-ray diffraction. Geophys

Res Lett 24:1831–1834

Yusa H, Inoue T, Ohishi Y (2000) Isothermal compressibility of

hydrous ringwoodite and its relation to the mantle discontinu-

ities. Geophys Res Lett 27:413–416

Zhang Y, Zhao D, Matsui M (2005) Anisotropy of akimotoite: a

molecular dynamics study. Phys Earth Planet Int 151:309–319


123

http://dx.doi.org/10.1029/2001JB000702

http://dx.doi.org/10.1002/0471721646.ch4

http://dx.doi.org/10.1002/0471721646.ch4

reprint - joseph smyth - university of colorado boulder

Documents