Emergent Negative Thermal Expansion in Amorphous Fe-Y-Zr-B Alloys

Area of Science:

• Materials Science
• Solid State Physics
• Magnetism

Background:

• Negative thermal expansion (NTE) is a rare phenomenon observed in crystalline materials like ceramics and metal-organic frameworks.
• NTE involves materials contracting when heated, contrary to typical thermal expansion.

Purpose of the Study:

• To report the unprecedented observation of NTE in an amorphous alloy.
• To investigate the origin and characteristics of NTE in amorphous metallic materials.

Main Methods:

• Synthesis and characterization of an amorphous Fe_{87.5}Y_{3}Zr_{1.5}B_{8} alloy.
• Measurement of thermal expansion over a wide temperature range.
• Extended X-ray Absorption Fine Structure (EXAFS) analysis.
• X-ray Pair Distribution Function (PDF) analysis.

Main Results:

• An unprecedented NTE was observed in the amorphous Fe_{87.5}Y_{3}Zr_{1.5}B_{8} alloy.
• The NTE phenomenon was significant, occurring over a wide temperature range (200-375 K) with a coefficient of α_{1}=-6.9×10^{-6} K^{-1}.
• NTE was found to be intrinsic to the amorphous structure and correlated with the iron magnetic moment.
• EXAFS indicated strong NTE for nearest-neighbor Fe-Fe pairs.
• PDF analysis suggested a tendency towards local ordered atomic arrangement in the amorphous alloy.

Conclusions:

• Amorphous alloys represent a novel class of materials exhibiting NTE.
• The observed NTE is driven by a complex interplay of local structure, magnetic interactions, and thermal relaxation.
• This discovery opens new avenues for scientific research and practical applications of NTE materials.