In step IV, the {200} plane collapses as the cumulative dose exceeds 40 e -Å -2 with a total displacement of 0.6 Å, as shown in fig. ). The {200} plane contains 6 ZnN4 tetrahedra per unit cell, less than the {211} Bragg plane having 8 ZnN4 tetrahedra per unit cell. Hence, the critical dose of {200} plane is lower than {211} Bragg plane. The {211} Bragg plane, which holds the 4MR with the 6MR, undergoes a total displacement of 0.6 Å before collapse at a cumulative dose greater than 45 e -Å -2 , as shown in fig. ). First principle calculations suggest that defect-triplet formation is more favorable in 6MR, whereas defectpair formation is preferred in 4MR. The rate of change in relative displacement per unit dose was 0.026 (1/e -Å -2 ), as measured in fig. ), presented in Table .