Mechanism of the B 3 to B 1 transformation in cubic AlN under uniaxial stress

Using ab initio calculations, we model the $B3$ to $B1$ phase transformation of cubic AlN in both tensile and shear deformations in order to obtain detailed information about the structure and the movement of the atoms within the cell. It is shown that, during that transformation, the strained $B3$ $(Imm2)$ structure changes to strained $B1$ $(I4∕mmm)$ structure as a result of a collective antiparallel movement of the Al and N atoms along the ⟨001⟩ crystallographic axis. The transition is discontinuous under uniaxial stress and the zero-stress transition state corresponds to a hypothetical state with a sudden lattice reconstruction.