First-principles calculation of defects structure in b2 NiTi

Abstract EN

First-principles electronic structure calculations have been performed for defect structure in non-stoichiometric B2 NiTi.

In order to determine the type of constitutional defects, the compositional dependence curves both of formation energies and of lattice parameters are obtained by the calculations employing super-cells in various sizes 16-atoms, 32-atoms and we have use the developed special quasi-random structures for random pseudo-binary A1-xBxC at compositions x = 0.25 and 0.5.

According to our results, Ni anti-sites are the constitutional point defects in Ni-rich side B2 NiTi and Ti anti-sites present the minimum energy for the Ti-rich side so Ni an Ti anti-sites are the more stable defects of B2 NiTi.

To investigate the thermal defect concentrations at finite temperatures, we adopted the Wagner-Schottky model using point defect formation enthalpies obtained from the SQS approaches.

The present results suggest that the predominant thermal defects of NiTi are an exchange defects type.

The calculated results show an agreement with the available theoretical and experimental data