Can twinning stabilize B19′ structure in NiTi martensite?

Although experimental observations determine the martensite structure of NiTi as monoclinic (B19′), ab-initio calculations show that, after a full optimization of the lattice, the ideal martensite structure relaxes into orthorhombic B33 one. This paper presents a first principles investigation of the structure of (100) compound twins in martensite. The results obtained by means of two different computational codes show that the optimized structure of twin cells is very close to that of B19′ martensite. This indicates that twinning can significantly contribute to mechanisms stabilizing the B19′ structure in real martensite samples.