Singh Sanjay, Dutta B, D'Souza S W, Zavareh M G, Devi P, Gibbs A S, Hickel T, Chadov S, Felser C, Pandey D
Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, D-01187, Dresden, Germany.
School of Materials Science and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi, 221005, India.
Nat Commun. 2017 Oct 18;8(1):1006. doi: 10.1038/s41467-017-00883-z.
The premartensite phase of shape memory and magnetic shape memory alloys (MSMAs) is believed to be a precursor state of the martensite phase with preserved austenite phase symmetry. The thermodynamic stability of the premartensite phase and its relation to the martensitic phase is still an unresolved issue, even though it is critical to the understanding of the functional properties of MSMAs. We present here unambiguous evidence for macroscopic symmetry breaking leading to robust Bain distortion in the premartensite phase of 10% Pt-substituted NiMnGa. We show that the robust Bain-distorted premartensite (T2) phase results from another premartensite (T1) phase with preserved cubic-like symmetry through an isostructural phase transition. The T2 phase finally transforms to the martensite phase with additional Bain distortion on further cooling. Our results demonstrate that the premartensite phase should not be considered as a precursor state with the preserved symmetry of the cubic austenite phase.
形状记忆合金和磁性形状记忆合金（MSMA）的预马氏体相被认为是具有保留奥氏体相对称性的马氏体相的前驱状态。尽管预马氏体相的热力学稳定性及其与马氏体相的关系对于理解MSMA的功能特性至关重要，但仍是一个未解决的问题。我们在此提供明确证据，证明在10%铂取代的NiMnGa的预马氏体相中存在导致强烈贝恩畸变的宏观对称性破缺。我们表明，强烈贝恩畸变的预马氏体（T2）相是通过同构相变从另一个具有类似立方对称性的预马氏体（T1）相产生的。进一步冷却时，T2相最终转变为具有额外贝恩畸变的马氏体相。我们的结果表明，预马氏体相不应被视为具有立方奥氏体相保留对称性的前驱状态。
