  Shape memory materials have the ability 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 a unique shape memory behavior in CaFe2As2,
which exhibits 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 class of shape
memory materials, ThCr2Si2-structured intermetallic compounds.
