Giant negative thermal expansion in a textured MnCoSi alloy

In the present work, textured stoichiometric MnCoSi alloys were fabricated by slow-cooling thermal treatment. Microstructure and crystallographic characterization revealed that the textured MnCoSi alloy consists of three different oriented orthorhombic TiNiSi-type martensite variants with their a(Orth)-axis lying in the cross-section of the rod-like MnCoSi alloy. A giant reversible linear negative thermal expansion (NTE) as much as 9350 ppm was achieved along the a(Orth)-axis of the textured MnCoSi alloy at a wide operation temperature span from 50 K to 400 K, owing to the antiferromagnetic arrangement. The linear NTE value slightly decreases from 9350 ppm to 9200 ppm with increasing the external magnetic field up to 2 T, which indicates that the present MnCoSi alloy demonstrates a stable NTE effect under external magnetic field. Moreover, during the martensitic transformation, the linear NTE along the a(Orth)-axis of the textured MnCoSi alloy could be up to 70,000 ppm at about 1200 K. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Textured stoichiometric MnCoSi alloys exhibit giant reversible linear negative thermal expansion (NTE) along the a(Orth)-axis, thanks to antiferromagnetic arrangement, achieving as much as 9350 ppm at a wide operation temperature span. The alloy demonstrates a stable NTE effect even under an external magnetic field, with the linear NTE value slightly decreasing with increasing magnetic field. Additionally, during martensitic transformation, the linear NTE along the a(Orth)-axis of the alloy could reach up to 70,000 ppm at approximately 1200 K.