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PRINCIPAL PUBLICATION AND AUTHORS

Synthesis of Single Crystals of ε-Iron and Direct Measurements of Its Elastic Constants, A. Dewaele (a,b), B. Amadon (a,b), A. Bosak (c), V. Svitlyk (c,d), F. Occelli (a,b), Phys. Rev. Lett. 131, 034101 (2023); https:/doi.org/10.1103/PhysRevLett.131.034101 (a) CEA DAM-DIF, Arpajon (France) (b) Université Paris-Saclay, CEA, Bruyères-le-Châtel (France) (c) ESRF (d) Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Dresden (Germany)

REFERENCES

[1] A. Dewaele et al., Phys. Rev. Lett. 97, 215504 (2006). [2] R. Fréville et al., Phys. Rev. B 107, 104105 (2023). [3] G. Steinle-Neumann et al., Nature 413, 57 (2001). [4] B. Martorell et al., Earth Planet. Sci. Lett. 365, 143 (2013).

that this anisotropy persists at the pressure conditions of the Earth s core (Figure 104b), which is consistent with observations of how seismic waves propagate through the planet.

In conclusion, this work takes advantage of the different mechanisms of solid solid phase transformations in iron [2] to control the microstructure of samples and obtain single crystals of the high-pressure ε-Fe phase through the α → γ → ε path. Direct measurements of ε-Fe single crystal elastic constants up to 33 GPa reveal a longitudinal velocity 4.4% lower in the basal plane. In parallel, a state-of-the-art technique for the modelling of bonding in correlated electronic systems was used to predict these elastic constants. They agree with the measured ones, which validates this description and

places dense iron ab initio modelling on firm footing. The crystalline elastic anisotropy of ε-Fe is predicted to persist up to the densities of Earth s inner core. By combining novel experimental and theoretical methods, this study advances our understanding of the composition and behaviour of the materials at the centre of our planet.

Fig. 104: a) Measured single-crystal elastic constants of ε-Fe plotted vs pressure P (squares) compared with the same constants calculated within standard DFT and DMFT frameworks. b) Predicted acoustic wave anisotropy for ε-Fe single crystals around 300 GPa (6.669 Å3/at) and 0 K with DMFT. The velocities of the longitudinal and two transverse waves are represented vs the angle of propagation to the hexagonal c axis. Literature predictions at 7.113 Å3/at [3] and 6.536 Å3/at [4] are also plotted.