Mechanism of the B3 to B1 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.