A First‐Principles Investigation of MgGeN2 Under Uniaxial Compression

Abstract

The structural, electronic, mechanical and optical properties of MgGeN2 under uniaxial compression are computationally investigated with density functional theory calculations. When the uniaxial compression is along [010] and [001] directions, there is no phase transition. For uniaxial compression along [100] direction, a phase transition is observed from orthorhombic to Pnma phase at 40 GPa. The resulting Pnma structure is in a vertically stacking graphene‐like structure. Moreover, the electronic structure and mechanical moduli show anisotropic for uniaxial compression in the [100], [010], and [001] directions. The bulk modulus monotonically increases and the shear modulus decreases for uniaxial compression in the [001] direction, while the bulk modulus goes to a maximum followed by a drop, and the shear modulus continuously decreases for uniaxial compression in the [010] and [100] directions. As phase transition occurs, both the bulk and shear moduli dramatically increase. The bandgap basically shows a monotonic increase and then gives a drop after arriving at a maximum. For compression in the [100] direction, the bandgap gives a more rapid increase near critical pressure. In addition, the light absorption decreases upon the uniaxial compressions. Therefore, uniaxial compression can be utilized to modulate the properties of MgGeN2 and help to widen its applications.

An Ab Initio Investigation of CdSnN2 Under Uniaxial Compressions

“…We think that inaccurate computations are to blame for the rise of the bandgap at 5 GPa since similar phenomena have been observed in ref. [30].…”

“…This is similar to the previous case of MgGeN 2 pressurized in [100] direction. [30] In a further step, the mechanical properties were investigated, where the bulk and shear moduli are defined as the Voigt-Reuss-Hill average. [44] M…”

“…Similar structures have been observed for XGeN 2 (X = Mg,Zn,Cd) and MSnN 2 (M = Mg,Zn). [ 19,29,30 ] The layer spacing is 2.318 Å at 30 GPa and reduces slowly as pressure further increases.…”

“…Similar behaviors were observed in our previous works. [ 30 ] For uniaxial compression in [010] direction, the VBM and CBM are nearly pinned so that the bandgap remains around 0.620 eV (see Figure 5b). For uniaxial compression in [001] direction shown in Figure 5c, a smaller bandgap is obtained with larger compression.…”

“…As shown in literatures, in some cases, applying stress or strain can effectively manipulate the electronic structure and mechanical properties of materials. [ 21–28 ] As for the II–IV–V 2 ceramics, it was recently discovered that XGeN 2 (X = Mg,Zn,Cd) and MSnN 2 (M = Mg,Zn) transit from structure to Pnma structure under uniaxial compression along [100] direction at a certain value, [ 19,29,30 ] where MgGeN 2 and MgSnN 2 can stabilize at the newly discovered Pnma phase after fully removing the compression. Based on this, thickness‐dependent thin films were constructed and studied on their electronic properties.…”