Pseudoelasticity of SrNi$_2$P$_2$ micropillar via Double Lattice Collapse and Expansion

TL;DR

This paper demonstrates that SrNi$_2$P$_2$ micropillars exhibit exceptional pseudoelasticity with a 14% recoverable strain due to reversible lattice transformations, surpassing typical crystalline solids and resembling shape memory alloys.

Contribution

It introduces a new high-performance ThCr$_2$Si$_2$-structured material exhibiting large pseudoelastic strains via a unique reversible lattice collapse-expansion mechanism.

Findings

Achieved ~14% recoverable strain in SrNi$_2$P$_2$ micropillars.

High yield strength (~3.8 GPa) and ultrahigh modulus of resilience (~146 MJ/m$^3$).

Stress-strain behavior similar to shape memory alloys.

Abstract

The maximum recoverable strain of most crystalline solids is less than 1% because plastic deformation or fracture usually occurs at a small strain. In this work, we show that a SrNi$_2$P$_2$ micropillar exhibits pseudoelasticity with a large maximum recoverable strain of ~14% under uniaxial compression via unique reversible structural transformation, double lattice collapse-expansion that is repeatable under cyclic loading. Its high yield strength (~3.8$\pm$0.5 GPa) and large maximum recoverable strain bring out the ultrahigh modulus of resilience (~146$\pm$19MJ/m$^3$) a few orders of magnitude higher than that of most engineering materials. The double lattice collapse-expansion mechanism shows stress-strain behaviors similar with that of conventional shape memory alloys, such as hysteresis and thermo-mechanical actuation, even though the structural changes involved are completely different. Our work suggests that the discovery of a new class of high performance ThCr$_2$Si$_2$-structured materials will open new research opportunities in the field of pseudoelasticity.