Decoding Earth's core. Scientists recreate iron monocrystals to study seismic variations

A while back, experts advanced a theory that the physical properties of epsilon-iron, the material Earth's core is made of, might be accountable for the planet's peculiar seismic behavior. "The inner core of Earth behaves anisotropically, meaning it displays varying characteristics in different directions. Consequently, seismic waves travel through the inner core at different velocities in the polar and equatorial directions," explains Jie Li, a mineral physicist at the University of Michigan in the USA.

A team of scientists from the University of Paris-Saclay in France has experimentally reproduced monocrystals of a high-pressure polymorph of iron, conducting the first-ever X-ray analysis of this material. The results of their research were published in the journal Physical Review Letters.

As reported by Chemistry World, the scientists exposed iron samples to immense pressure (roughly 101,526 PSI) and heat (around 1526.33°F), resulting in stable epsilon-iron monocrystals. This structure permitted the X-ray analysis and testing of its stress and elastic properties.

Agnès Dewaele from the University of Paris-Saclay explains that a single crystal of epsilon-iron is challenging to create directly from the surrounding alpha-iron because the transformation destroys single crystals. "Instead of attempting a direct transformation, we passed through a third phase, known as gamma-iron, which is only stable at high temperatures. This way, we could maintain samples in the form of a monocrystal," she adds.

The experimental measurements confirmed the scientists' earlier suspicions. According to the research, epsilon-iron demonstrates directional elasticity - vibrations travel approximately 4.4 percent faster along one axis of the crystal compared to measurements taken relative to another axis of the crystal.