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

•Computationally investigated ZnGeN2 and CdGeN2 under uniaxial compression.•Phase transition occurs and arrives at layered high pressure phase.•The band gap increases along with compression and decreases due to the formation of new inter-layer bonds. 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.