Enhanced negative thermal expansion of boron-doped Fe₄₃Mn₂₈Ga_28.97B_0.03 alloy

Enhanced negative thermal expansion (NTE) properties are achieved by introducing a little amount of boron in the Fe₄₃Mn₂₈Ga_28.97B_0.03 alloy. As a result, this alloy shows a giant NTE coefficient of α_l = −79.7 × 10⁻⁶ K⁻¹ in a wide temperature range from 277 K to 136 K. Compared to the NTE characteristics in Fe₄₃Mn₂₈Ga₂₉, the NTE operation temperature window has expanded by 74% with the corresponding coefficient of thermal expansion increased by 57% within the NTE temperature window for the boron-doped Fe₄₃Mn₂₈Ga_28.97B_0.03. In-situ synchrotron high-energy X-ray diffraction results suggest that by boron substitution, the large unit cell volume change across martensitic transformation and the wide phase transition temperature interval are responsible for the pronounced NTE behavior in Fe₄₃Mn₂₈Ga_28.97B_0.03. Moreover, for the Fe₄₃Mn₂₈Ga_28.97B_0.03 NTE material, the compressive strength and strain are significantly improved compared with that of Fe₄₃Mn₂₈Ga₂₉. The present study indicates that Fe₄₃Mn₂₈Ga_28.97B_0.03 with enhanced NTE across martensitic transformation may be used for practical application as thermal-expansion compensators.