Jung-Fu Lin1,4,
Viktor V. Struzhkin1,
Steven D. Jacobsen1,
Michael Y. Hu2,
Paul Chow2,
Jennifer Kung3,
Haozhe Liu2,
Ho-kwang Mao1
and Russell J.
Hemley1
- Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington DC 20015, USA
- HPCAT, Carnegie Institution of Washington, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
- The Mineral Physics Institute, University of New York at Stony Brook, Stony Brook, New York 11794, USA
- †Present address: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
Correspondence to: Jung-Fu Lin, Email: j.lin@gl.ciw.edu
Iron is the most
abundant
transition-metal
element in the
mantle and
therefore plays
an important
role in the
geochemistry and
geodynamics of
the Earth's
interior.
Pressure-induced
electronic spin
transitions of
iron occur in
magnesiowüstite,
silicate
perovskite and
post-perovskite.
Here we have
studied the spin
states of iron
in
magnesiowüstite
and the isolated
effects of the
electronic
transitions on
the elasticity
of
magnesiowüstite
with
in situ
X-ray emission
spectroscopy and
X-ray
diffraction to
pressures of the
lowermost
mantle. An
observed
high-spin to
low-spin
transition of
iron in
magnesiowüstite
results in an
abnormal
compressional
behaviour
between the
high-spin and
the low-spin
states. The
high-pressure,
low-spin state
exhibits a much
higher bulk
modulus and bulk
sound velocity
than the
low-pressure,
high-spin state;
the bulk modulus
jumps by ~35 per
cent and bulk
sound velocity
increases by ~15
per cent across
the transition
in (Mg0.83,Fe0.17)O.
Although no
significant
density change
is observed
across the
electronic
transition, the
jump in the
sound velocities
and the bulk
modulus across
the transition
provides an
additional
explanation for
the seismic wave
heterogeneity in
the lowermost
mantle. The
transition also
affects current
interpretations
of the
geophysical and
geochemical
models using
extrapolated or
calculated
thermal
equation-of-state
data without
considering the
effects of the
electronic
transition.