We use ab-initio calculations to study the role of stacking faults in connecting the high temperature B2 and the theoretically-predicted low temperature B33 NiTi phases. In contrast with prior work, we describe the $B2\to B33$ phase transformation in terms of alternate bilayer shifts by on the (011) ${}_{B2}$ plane, obtaining a viable pathway; the same mechanism could also work with the B19 parent phase. We then examine B33-like structures built from alternate stacking sequences of B19 bilayers, constructed to have monoclinic tilt angles close to the experimentally-reported NiTi B19’ martensite, and find four low-energy stacking fault variants with energies 5.8-8.5 meV/atom above the calculated B19’martensite structure, suggesting that such structures might appear as a part of NiTi martensite phase at low temperatures. Investigating further the occurrence of specific coordinated planar shifts in NiTi systems, we discover dynamically stable NiTi B27 phase and find that it is only 1.2 meV/atom above the calculated B33 ground state structure, thus having a potential to also play a role in NiTi martensitic phase transformation.

中文翻译：

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形状记忆合金NiTi的堆垛层错和交替晶体结构

我们使用从头算计算来研究堆垛层错在连接高温B2和理论上预测的低温B33 NiTi相中的作用。与先前的工作相反，我们描述了$乙2\to 乙33$ （011）上的交替双层位移的相位变换 ${}_{乙2}$飞机，获得可行的路径；B19父阶段也可以使用相同的机制。然后，我们研究了由B19双层的交替堆叠序列构建的B33样结构，其构造具有接近于实验报告的NiTi B19'马氏体的单斜倾斜角，并发现了能量为5.8-8.5 meV / atom的四个低能堆叠断层变体。高于计算出的B19'马氏体结构，表明这种结构可能在低温下作为NiTi马氏体相的一部分出现。进一步研究NiTi系统中特定的协调平面位移的发生，我们发现了动态稳定的NiTi B27相，发现它仅比计算出的B33基态结构高1.2 meV /原子，因此有可能在NiTi马氏体中起作用相变。