Superelasticity and Cryogenic Linear Shape Memory Effects of CaFe2As2

Shape memory materials have the capability to recover their original shape after a significant amount of deformation when they are subjected to certain stimuli, for instance, heat or magnetic fields. However, their performance is often limited by the energetics and geometry of the martensitic-austenitic phase transformation. Here, we report the discovery of a unique shape memory behavior in CaFe2As2, which exhibits unprecedented superelasticity with over 13% recoverable strain, over 3 GPa yield strength, repeatable stress-strain response even at the micrometer scale, and cryogenic linear shape memory effects near 50 K. These properties are acheived through a reversible uni-axial phase transformation mechanism, the tetragonal/orthorhombic-to-collapsed tetragonal phase transformation. Our results offer the possibility of developing cryogenic linear technologies with a high precision and high actuation power per-unit-volume for deep space exploration, and more broadly, suggest a mechanistic path to a whole new class of shape memory materials, ThCr2Si2-structured intermetallic compounds.