Twin Boundary in hcp Crystals: Quantum and Thermal Behavior

Abstract

The 180°twin boundary (TB) (stacking fault) is investigated in the hexagonal close-packed (hcp) light materials. It is shown that atomic symmetry inside the twin boundary is lower than in hcp phase due to interatomic interaction between neighbors. In the case of quantum or thermal behavior, for the isosurfaces, an initial spherical form (in hcp phase) transforms into ellipsoid (in the boundary). We introduce the isosurface deformation parameter. The self-consistent description is developed to estimate the parameters of the thermodynamic potential, and the models of hard spheres and ellipsoids are used. It is shown that the quantum or thermal behavior of the boundary atoms causes the following effects: (i) the increase of degree of overlap of the atomic wave functions or trajectories within the twin boundaries, (ii) the increase of diffusion inside the twin boundaries, and (iii) the decrease of energy and broadening of the quantum boundary in comparison with the classical case.