Targeting Superior Zero Thermal Expansion Material by the Concept of TRIP‐Invar

A key challenge for spin‐dominated functional materials is their suboptimal structural properties, a problem that restricts their widespread applications. Here, this limitation is addressed by introducing additional lattice degree of freedom. This is exemplified in a novel cobalt‐based alloy, which is targeted to demonstrate both the spin‐state transformation‐induced zero thermal expansion (Invar effect, ensuring precision) and lattice transformation‐induced plasticity (TRIP effect, enhancing safety), referred to as TRIP‐Invar. An unusual martensitic transformation exhibiting three‐phase coexistence has been observed under stressing at 77 K, which results in pronounced work hardening behavior and exceptional cryogenic toughness. Notably, reversible spin/lattice transformations enable intrinsic thermal repairability. This findings not only expand the categories within the Invar family, but also provide a reference for the discovery of other integrated structural and functional materials, enabling humanity's exploration of extreme environments like the poles and deep space.