The role of the lattice in the $\gamma \to \alpha$ phase transition of Ce: a high pressure neutron and x-ray diffraction study

TL;DR

This study investigates the lattice dynamics and their role in the gamma to alpha phase transition of cerium using high-pressure neutron and x-ray diffraction, highlighting the significance of lattice vibrations in the transition.

Contribution

It provides detailed measurements of lattice parameters and vibrational entropy, emphasizing the importance of lattice vibrations alongside electronic factors in cerium's phase transition.

Findings

Vibrational entropy change is about half of the total entropy change.

Bulk modulus follows a power-law pressure dependence.

Lattice vibrations are crucial for understanding the phase transition.

Abstract

The temperature and pressure dependence of the thermal displacements and lattice parameters were obtained across the $\gamma \to \alpha$ phase transition of Ce using high-pressure, high-resolution neutron and synchrotron x-ray powder diffraction. The estimated vibrational entropy change per atom in the $\gamma \to \alpha$ phase transition, $\Delta S^{\gamma - \alpha}_{\rm vib} \approx (0.75 \pm 0.15)$k$_{\rm B}$, is about half of the total entropy change. The bulk modulus follows a power-law pressure dependence which is well described using the framework of electron-phonon coupling. These results clearly demonstrate the importance of lattice vibrations, in addition to the spin and charge degrees of freedom, for a complete description of the $\gamma \to \alpha$ phase transition in elemental Ce.