Local chemical disorder as the origin of anomalous thermal expansion in TiFe2 Laves phase alloys

Abstract

TiFe₂ alloys, a C14 Laves phase system, exhibit negative or zero thermal expansion (NTE/ZTE) despite the absence of the first-order transitions that typically drive such behavior in related compounds. Across the compositional range, the magnetic ground state evolves from ferromagnetic ordering in Fe-rich alloys to antiferromagnetic ordering in Ti-rich variants, yet the thermal expansion response remains invariant. High-resolution synchrotron X-ray and neutron diffraction detect no anomalies in lattice volume or magnetic moment, and Rietveld refinements exclude significant antisite disorder. In contrast, Fe and Ti K-edge extended X-ray absorption fine structure (EXAFS) and elemental mapping via energy-dispersive X-ray spectroscopy (EDAX) reveal pronounced nanoscale compositional inhomogeneity, forming Fe-rich and Ti-rich regions. The coexistence of competing ferro- and antiferromagnetic interactions from these chemically distinct domains gives rise to an invar-like effect below a characteristic temperature, T*. These results establish local chemical disorder as a key mechanism for stabilizing NTE/ZTE behavior in intermetallic systems, independent of long-range structural or magnetic transitions.