Physicists have synthesized crystals of the substance we think is at the core of the Earth: ScienceAlert

Using a diamond anvil, physicists have succeeded in compressing iron into the shape we think exists deep in the center of the Earth.

it’s called Hexagonal chop, or epsilon iron (ϵ-Fe), which is only stable at extremely high pressures. Scientists believe that the majority of the iron in Earth’s core takes this shape, and a detailed understanding of its properties can help us understand why there are directional differences in the center of our planet – a property known as anisotropy.

There is only one problem with this quest to understand the Earth’s core. Here at the surface, in a relatively nice and low atmospheric pressure regime, conditions are difficult to replicate in the core. But we can create high pressure conditions for short time pulses, using diamond anvils and heat.

Here we report the synthesis of ϵ-Fe single crystals in diamond anvil cells and the subsequent measurement of single-crystal elastic constants for this phase up to 32 GPa at 300 K with inelastic X-ray scattering. Write a team led by physicist Agnès Dewaele from Paris-Saclay University in France.

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The challenge is to convert the atmospheric pressure phase of the so-called iron ferrite, or alpha iron. Usually, when high pressure is applied to ferrite in an attempt to crush it into a hexagonal shape, it breaks into small crystals unsuitable for detailed analysis, frustrating efforts to study its elastic properties.

Therefore, Diwali and her colleagues approached the problem step by step. They placed ferrite crystals in a diamond anvil in a vacuum heater, and increased the pressure to 7 gigapascals (about 70,000 times atmospheric pressure at sea level) and the temperature to 800 K (527 degrees Celsius, or 980 Fahrenheit).

This produced an intermediate phase of iron occurring at high temperatures in called atmospheric conditions austenite;, or gamma iron. Austenite has a different structure than ferrite, and the austenite crystals made by the team changed into a smoother hexagonal phase at pressures between 15 and 33 gigapascals at 300 K.

Next, they used the synchrotron beamline at the European Synchrotron Radiation Facility to probe the sextants and analyze their properties.

What we know about Earth’s core is largely reconstructed based on seismic data. Sound waves from planetary tremors propagate differently through different materials; This is how we know that the Earth’s core is divided into layers like a jaw.

But for a more detailed understanding, we need to know what the material in the core really is, and how it responds to sound waves. Dewaele and her team’s work showed that hexaferrum’s elasticity depends on orientation; Waves propagate faster along a particular axis.

This asymmetry persists during pressure changes as well, suggesting that it is also how the hexagon behaves in up to 360 GPa the inner kernel environment. This is consistent with observations of how seismic waves travel across the planet.

The results indicate that the team’s techniques could make an excellent probe for understanding the extreme conditions at the center of our universe.

Research published in Physical review letters.