0 10 20 30 40 50 60 70 80 90 10032

34

36

38

40

42

44

46

48

K0=199(6) GPaK0=221(3) GPa

Low spin

Fe0.5 Mg

0.5 Al0.5 Si

0.5 O3

Vo

lum

e p

er

form

ula

un

it (

Å3)

Pressure (GPa)

Fe0.96 M

g0.5 Si

0.54 O3

High spin

0.02 0.03 0.04 0.05 0.06 0.07 0.08165

170

175

180

185

190

195

200

205

210

Norm

aliz

ed

Pre

ssure

(G

Pa

)

Strain

40 GPa

Structure, crystal chemistry, and compressibility of iron-rich silicate perovskite at pressures up to 95 GPa.

I. Koemets1, Z. Liu2, E. Koemets1, B. Wang1, C. McCammon1, T. Katsura1, M. Hanfland3, A. Chumakov3, L. Dubrovinsky1

10 20 30 40 50 60

7

8

9

10

15

16

17

18

oB (Al0.5Si0.5)

pA (Fe0.61Mg0.39)

oB (Si)

oB (Fe0.7Mg0.22Si0.08)

Po

lyh

ed

ral vo

lum

e (

Å3)

Pressure (GPa)

pA (Fe0.5Mg0.5)

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

This study:

Al-free sample

Fe3+ on pA-site

Fe3+ on oB-site

Al-rich sample:

Fe3+ on pA-site

Fe2+ on pA-site

Previous studies:

Sinmyo et al. 2017

Liu et al. 2018

Potapkin et al. 2013

High spin

oB-site Fe3+

pA-site Fe2+

Ce

ntr

e s

hift (m

m/s

)

Quadrupole splitting (mm/s)

pA-site Fe3+

Low spin

1. IntroductionBridgmanite elasticity is influenced by chemical composition,

oxygen vacancies, and pressure-induced high-spin to low-spintransition in iron. The effect of pressure-driven spin transition(s) iniron-bearing bridgmanite on bulk modulus is complex, because ironcould occupy different crystallographic sites and can occur as bothferrous and ferric. In addition, high-pressure experiments with silicateperovskite end-members could provide us with a self-consistentelasticity database and clarify mechanism(s) of cations substitution.

2. MethodsSamples synthesis in Large Volume Press, diamond anvil cells for

pressure generation, synchrotron radiation based in situ single-crystalX-ray diffraction, and Mössbauer spectroscopy.

4. Results: Compressibility

Cold compression behaviour of Fe0.5Mg0.5Si0.5Al0.5O3 and Fe0.96Mg0.5Si0.54O3

Black lines represent fits of P-V data with second order Birch-Murnaghan EoS. Blue lines aredata from (Lin et al., 2000).At pressures above ~10 GPa samples with both compositionstransform to (pseudo) orthorhombic perovskite-type structured phases. Inset: Above 40 GPasoftening of the phase is obvious and related to spin transition of Fe3+ located in the B’-site of

double-perovskite.

3. Results: Structures and their relations

Crystal structures of Fe0.5Mg0.5Al0.5Si0.5O3 (a, b) and Fe0.96Mg0.5Si0.54O3 (c, d) silicate phases and their structural relations (a,c) Phases stable at P<10 GPa, (b,d) Phases stable at P>10 GPa. Distinguishable crystallographic sites are different in color. pA refers to prismatic A-site, oB and oB’ refers to octahedral B- and B’-site

5. Results: Crystal chemistry

Compressibility of individual polyhedra in Al-rich silicate perovskite (black) and Al-poor silicate double perovskite (red).

6. Results: Mössbauer spectroscopy

A summary of quadrupole splitting and centre shift of silicate perovskite samples at highpressure.For comparison, we plotted data from previous studies involving data collection on Fe-bearingbridgmanites. Liu et al. 2018 (stars) used nuclear forward scattering; Sinmyo et al. 2017(crosses) and Potapkin et al. 2013 (triangles) used SMS.

Key points: First silicate double-perovskite New corundum-structure derivative Fe,Mg-bearing octahedral site in dPv

1 University of Bayreuth, Bayreuth, Germany 2 Jilin University, Changchun, China 3 ESRF, Grenoble, France