  ThCr2Si2-type intermetallic compounds are known to exhibit superelasticity
associated with structural transitions through lattice collapse and expansion.
These transitions occur via the formation and breaking of Si-type bonds,
respectively, under uniaxial loading along the [0 0 1] direction. Unlike most
ThCr2Si2-type intermetallic compounds, which have either an uncollapsed
tetragonal structure or a collapsed tetragonal structure, SrNi2P2 possesses a
third type of collapsed structured: a one-third orthorhombic structure, for
which one expects the occurrence of unique structural transitions and
superelastic behavior. In this study, uniaxial compression and tension tests
were conducted on micron-sized SrNi2P2 single crystalline columns at room
temperature, 200K, and 100K, to investigate the influence of loading direction
and temperature on the superelasticity of SrNi2P2. Experimental data and
density functional theory calculations revealed the presence of
tension-compression asymmetry in the structural transitions and
superelasticity, as well as an asymmetry in their temperature dependence, due
to the opposite superelastic process associated with compression (forming P-P
bonds) and tension (breaking P-P bonds). Additionally, following
thermodynamics, the observations suggest that this asymmetric superelasticity
could lead to an opposite elastocaloric effect between compression and tension,
which could be beneficial potentially in obtaining large temperature changes
compared to conventional superelastic solids that show the same elastocaloric
effect regardless of loading direction. These results provide an important
fundamental insight into the structural transitions, superelasticity processes,
and potential elastocaloric effects in SrNi2P2.
