Compression-induced phase transition of GaN bulk from wurtzite phase to five-fold coordination hexagonal phase

The phase transformation of GaN bulk from the Wurtzite phase (WZ) to the hexagonal phase (HX) is studied by molecular dynamics simulation. The mechanical response and atomic structural evolution of transition are analyzed in detail. In addition, the loading rate effect on the phase transition is determined, that is, the phase transition ratio declines with a decrease of the strain rate. The WZ GaN bulk completely transforms into the HX phase in the case of compression at an ultrahigh strain rate. However, at a relatively slower strain rate, the HX phase of GaN partly nucleates and the untransformed regions are proved to be elastic deformed regions. Combined with an energy analysis, two atomic movement modes are recognized as the inducements for the phase transition and formation of elastic deformed regions. The first mode, which is responsible for the formation of elastic deformed regions, is an atomic sliding motion along the c {0001} planes. The second mode is a radial stretching atomic motion. The radial stretching motion, which requires a lot of energy, induces the WZ-HX phase transition. Moreover, the phase transition is affected drastically by the rise of temperature.