Anomalous elastic properties across the γ to α volume collapse in cerium.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 29084963.
- Also identified by DOI 10.1038/s41467-017-01411-9 and PMC identifier 5662743.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The behavior of the f-electrons in the lanthanides and actinides governs important macroscopic properties but their pressure and temperature dependence is not fully explored. Cerium with nominally just one 4f electron offers a case study with its iso-structural volume collapse from the γ-phase to the α-phase ending in a critical point (p <sub>C</sub>, V <sub>C</sub>, T <sub>C</sub>), unique among the elements, whose mechanism remains controversial. Here, we present longitudinal (c <sub>L</sub>) and transverse sound speeds (c <sub>T</sub>) versus pressure from higher than room temperature to T <sub>C</sub> for the first time. While c <sub>L</sub> experiences a non-linear dip at the volume collapse, c <sub>T</sub> shows a step-like change. This produces very peculiar macroscopic properties: the minimum in the bulk modulus becomes more pronounced, the step-like increase of the shear modulus diminishes and the Poisson's ratio becomes negative-meaning that cerium becomes auxetic. At the critical point itself cerium lacks any compressive strength but offers resistance to shear.