Phase transition and electronic properties of XGeN2 (X = Zn,Cd) under uniaxial compression

Ternary nitrides ZnGeN2 and CdGeN2 were computationally investigated under uniaxial compressions in [100] direction using first principles calculations. Phase transition from Pna21 to Pnma structure occurs for ZnGeN2, while CdGeN2 transforms to a quasi-layered Pna21 structure with distorted in-plane hexagons. For both the compounds, the band gap first increase and then decrease along with increasing compression. However, the band gap of ZnGeN2 monotonically increases until the phase transition occurs at 70 GPa and then decreases, while CdGeN2 shows a maxima around 30 GPa followed with a reduction. Moreover, for both the compounds, the band gap transforms from direct to indirect under uniaxial compression, and the electron correlation becomes weaker and weaker. It was also confirmed that the compressed structures of ZnGeN2 and CdGeN2 will restore their initial structures at ambient conditions when removing the compression, which differs to the cases of MgGeN2 and MgSnN2.

Automated summary

Ternary nitrides ZnGeN2 and CdGeN2 were investigated computationally under uniaxial compressions in [100] direction. The results showed that ZnGeN2 undergoes a phase transition from Pna21 to Pnma structure, while CdGeN2 transforms to a quasi-layered Pna21 structure with distorted in-plane hexagons. The band gap of both compounds first increases and then decreases with increasing compression, and transitions from direct to indirect under uniaxial compression. Additionally, the electron correlation becomes weaker as the compounds are compressed.