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NEWS

December 2023 ESRFnews

Core iron probed

of iron in a hexagonal close-packed

structure, known as ε-iron, which has

preferred crystalline orientations.

Studying εiron is tricky as during

compression from its initial body

centred cubic crystalline phase known

as αphase iron typically fractures

into numerous small crystals that

undergo plastic deformation Agnès

Dewaele of the University of Paris

Saclay and colleagues have avoided this

by heating αphase iron at constant

pressure until it reaches a facecentred

cubic or γphase The researchers

then pressurised this phase at constant

temperature before cooling at

constant pressure to achieve εiron

They characterised it by angular-

dispersive X-ray diffraction at the

ID27 beamline and inelastic scattering

at the ID28 beamline

Unlike previous studies on

powdered iron samples Dewaele

and colleagues data gave precise

estimations of the anisotropy

present in the elastic constants of

εiron qualitatively agreeing with

prior works that have identified the

direction with which waves propagate

most rapidly However there were

quantitative deviations from previous

data highlighting the importance of

their experimental approach Phys

Rev Lett 131 034101

ESRF users from France have

synthesised a single-crystalline

iron in the structure that it likely

assumes in Earths core Their Xray

measurements will help to hone

theories about why seismic waves

travel at different speeds through

the Earth

Seismology suggests that the

Earths core is solid in the middle

and liquid towards the outside It

also suggests that the structure is

anisotropic as seismic waves travel

faster in the polar direction than

in the equatorial direction One

explanation for this is that the solid

inner core is predominantly composed

S H U T T E R S T O C K/R O S T 9

“Researchers

characterised the

iron using

angular

dispersive Xray

diffraction at the

ID27 beamline

and inelastic

scattering at the

ID28 beamline