Scientists Use Diamond Anvil to Create Hexaferrum, Shedding Light on Earth’s Core
Using cutting-edge technology, physicists have successfully transformed iron into a unique form called hexaferrum, providing valuable insights into the composition and properties of Earth’s core. This breakthrough could help us understand the directional variations in texture observed in the center of our planet, a phenomenon known as anisotropy.
Hexaferrum, also known as epsilon iron (ϵ-Fe), is only stable under extremely high pressures. It is believed that the majority of the iron in Earth’s core exists in this form. However, replicating such high-pressure conditions on the surface is a formidable challenge. To overcome this hurdle, scientists employed a diamond anvil and heat to create brief pulses of high-pressure environments.
Under the leadership of physicist Agnès Dewaele from the University of Paris-Saclay in France, the team succeeded in synthesizing single crystals of ϵ-Fe in diamond anvil cells. They also measured the single-crystal elastic constants of this phase at pressures up to 32 GPa (gigapascals) and a temperature of 300 Kelvin using inelastic X-ray scattering.
The main obstacle in studying Earth’s core lies in converting the atmospheric pressure phase of iron called ferrite, or alpha iron, into hexaferrum. Usually, when high pressure is applied to ferrite, it fractures into tiny crystals that are unsuitable for detailed analysis. Dewaele and her colleagues took a stepwise approach to tackle this problem.
They placed crystals of ferrite in a diamond anvil within a vacuum heater and increased the pressure to 7 GPa and the temperature to 800 Kelvin. This produced an intermediate phase of iron known as austenite, or gamma iron. The austenite crystals transitioned smoothly into the hexaferrum phase between 15 and 33 GPa at 300 Kelvin.
To analyze the properties of hexaferrum, the team utilized a synchrotron beamline at the European Synchrotron Radiation Facility. The study revealed that hexaferrum’s elasticity is directionally dependent, with waves propagating faster along one specific axis. Importantly, this anisotropy persisted even during pressure changes, indicating its behavior in the extreme conditions of the inner core, where pressures can reach up to 360 GPa.
The findings align with seismic data and provide crucial information for understanding the composition and behavior of Earth’s core. While seismic data has already revealed a layered structure within the core, a detailed understanding requires knowledge of the actual material present and how it responds to acoustic waves. The team’s techniques using hexaferrum could serve as an excellent probe, shedding light on the extreme conditions at the center of our world.
This groundbreaking research, led by Agnès Dewaele, has been published in Physical Review Letters. The study showcases the extraordinary capabilities of modern technology in unraveling the mysteries hidden deep within our planet.