Kinetics of the isostructural γ to α transition in cerium investigated by ultrasonics

Abstract

We performed ultrasonic pulse echo measurements on high-purity polycrystalline cerium across the isostructural γ to α-fcc-to-fcc transition, up to 13 kbar and then back down to 0.3 kbar. Our results confirm the anomalous decrease of the longitudinal sound velocity in the γ-phase approaching the transition, a significant hysteresis loop, and definitively highlight the strong difference in the long wavelength limit of the lattice dynamics of the γ and α phases. We have also studied the kinetics of the transition, which is well described by an Arrhenius behavior, with an activation volume of 10 cm³/mol.

Keywords:

• cerium
• phase transition
• kinetics

Acknowledgements

We thank F.J. Ryerson for access to various apparatus used in this study. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Notes

This might be strictly true only for the 2–3% difference measured at 11 and 12 kbar. In the other cases, the larger difference might arise from the simultaneous presence in different ratios of both γ - and α -phases (see discussion later on).