Local chemical disorder as the origin of anomalous thermal expansion in TiFe2 Laves phase alloys
M. Azavedo (Goa University)
E. T. Dias (Goa University)
V. Srihari (Bhabha Atomic Research Centre)
Robert Dankelman (TU Delft - RID/TS/Technici Pool)
I. Dhiman (TU Delft - RID/TS/Instrumenten groep, TU Delft - Applied Sciences)
K. R. Priolkar (Goa University, UGC-DAE Consortium for Scientific Research)
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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.