fig9

Figure 9. Schematic mechanism of the NTE in zinc-blend structure. (A) A cubic unit cell of zinc blende structure, (B) schematic view of the transverse acoustic vibrational mode around the X point in the Brillouin zone, and (C) look of atoms 1 and 2 along the axis. In (B), the vibrational motions of atoms 1 and 2 are in antiphase. In (C), R₀ and R (R₀’ and R’) in the left (right) are initial (relaxed) equilibrium and instantaneous interatomic distances, respectively. Due to the vibrational instability, the lattice is consequently contracted.