Martensitic-like microstructures across the isostructural phase transitions in Cerium

The isostructural gamma – alpha phase transition in elemental cerium is an electronic transition caused by a delocalization of the 4f electrons. This affects the bonding properties of Ce atoms and leads to a large volume collapse reaching ∼17% in the low pressure regime (¡ 2 GPa). While great attention has been drawn on the electronic description of this transition, attempts to understand the mesoscale mechanisms of this structural transition and their consequences in terms of microstructure remain scarce. We have investigated this transition by means of combined X-ray Computed Tomography and Energy Dispersive X-ray Diffraction on polycrystalline samples. Our experimental observations reveal a platelet-shape microstructure across the transition and up to the critical point, which have been associated to displacive mechanisms. Based on continuum mechanics modeling and ab initio calculations, we propose that here, this microstructure is initiated by elastic instability and shear anisotropy in the ¡100¿ directions.